diff --git a/Source/JavaScriptCore/Scripts/check-xcfilelists.sh b/Source/JavaScriptCore/Scripts/check-xcfilelists.sh
index dd88053..89fbdd5d 100755
--- a/Source/JavaScriptCore/Scripts/check-xcfilelists.sh
+++ b/Source/JavaScriptCore/Scripts/check-xcfilelists.sh
@@ -8,6 +8,7 @@
 [ "${USE_INTERNAL_SDK}" == "YES" ] || { echo "### Not running because USE_INTERNAL_SDK is not YES"; exit 0; }
 
 SCRIPT="${BUILD_SCRIPTS_DIR}/generate-xcfilelists"
+[ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../../${WK_ADDITIONAL_SCRIPTS_DIR}/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../Tools/Scripts/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || { echo "### Cannot find generate-xcfilelists script"; exit 1; }
 
diff --git a/Source/WebCore/Scripts/check-xcfilelists.sh b/Source/WebCore/Scripts/check-xcfilelists.sh
index 9aa9206..9356964 100755
--- a/Source/WebCore/Scripts/check-xcfilelists.sh
+++ b/Source/WebCore/Scripts/check-xcfilelists.sh
@@ -8,6 +8,7 @@
 [ "${USE_INTERNAL_SDK}" == "YES" ] || { echo "### Not running because USE_INTERNAL_SDK is not YES"; exit 0; }
 
 SCRIPT="${BUILD_SCRIPTS_DIR}/generate-xcfilelists"
+[ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../../${WK_ADDITIONAL_SCRIPTS_DIR}/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../Tools/Scripts/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || { echo "### Cannot find generate-xcfilelists script"; exit 1; }
 
diff --git a/Source/WebKit/Scripts/check-xcfilelists.sh b/Source/WebKit/Scripts/check-xcfilelists.sh
index 46fb061..cc371fa 100755
--- a/Source/WebKit/Scripts/check-xcfilelists.sh
+++ b/Source/WebKit/Scripts/check-xcfilelists.sh
@@ -8,6 +8,7 @@
 [ "${USE_INTERNAL_SDK}" == "YES" ] || { echo "### Not running because USE_INTERNAL_SDK is not YES"; exit 0; }
 
 SCRIPT="${BUILD_SCRIPTS_DIR}/generate-xcfilelists"
+[ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../../${WK_ADDITIONAL_SCRIPTS_DIR}/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../Tools/Scripts/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || { echo "### Cannot find generate-xcfilelists script"; exit 1; }
 
diff --git a/Tools/ChangeLog b/Tools/ChangeLog
index 547a1b9..c5e4f8f 100644
--- a/Tools/ChangeLog
+++ b/Tools/ChangeLog
@@ -1,3 +1,175 @@
+2019-05-15  Keith Rollin  <krollin@apple.com>
+
+        Rewrite generate-xcfilelists in Python
+        https://bugs.webkit.org/show_bug.cgi?id=197622
+        <rdar://problem/50508222>
+
+        Reviewed by Jonathan Bedard, Alex Christensen.
+
+        For a number of reasons, rewrite generate-xcfilelists in Python:
+
+        - The previous bash script was large and unmaintainable.
+        - We have more internal expertise with Python than with bash.
+        - The bash script used temporary files in /tmp that got stranded and
+          were owned by root, making them awkward to clear out.
+          <rdar://problem/49490262>
+        - We needed to complete support for engineers that built with Xcode
+          rather than the command line.
+        - There are some bugs leading to mildly corrupted .xcfilelist files.
+          It's not apparent the source of the bugs, but one general reason
+          might be due to approaches born of using bash. Rewriting in Python
+          may clear these up.
+
+        * Scripts/generate-xcfilelists:
+        * Scripts/webkitpy/common/attribute_saver.py: Added.
+        (AttributeSaver):
+        (AttributeSaver.__init__):
+        (AttributeSaver.__enter__):
+        (AttributeSaver.__exit__):
+        * Scripts/webkitpy/common/attribute_saver_unittest.py: Added.
+        (AttributeSaverTest):
+        (AttributeSaverTest.SimpleTestClass):
+        (AttributeSaverTest.SimpleTestClass.__init__):
+        (AttributeSaverTest.test_class):
+        (AttributeSaverTest.test_normal_default):
+        (AttributeSaverTest.test_normal_value):
+        (AttributeSaverTest.test_normal_value_on_exception):
+        (AttributeSaverTest.test_normal_value_on_normal_exit):
+        (AttributeSaverTest.test_normal_value_with_finally_on_exception):
+        (AttributeSaverTest.test_normal_value_with_finally_on_normal_exit):
+        (AttributeSaverTest.test_normal_value_with_else_on_exception):
+        (AttributeSaverTest.test_normal_value_with_else_on_normal_exit):
+        * Scripts/webkitpy/generate_xcfilelists_lib/__init__.py: Added.
+        * Scripts/webkitpy/generate_xcfilelists_lib/application.py: Added.
+        (Application):
+        (Application.__init__):
+        (Application.run):
+        (Application._initialize):
+        (Application._initialize.collect_attributes):
+        (Application._create_parser):
+        (_validate_args):
+        (_cmd_generate):
+        (_cmd_check):
+        (_cmd_subgenerate):
+        (_cmd_help):
+        (_do_generate):
+        (_do_merge):
+        (_report_results):
+        (_report_merge_results):
+        (_report_remediation_steps):
+        (_report_remediation_steps.add_to_message):
+        (_any_have_errors):
+        (_any_have_actions):
+        (_log_progress):
+        (_log_results):
+        (get_generate_xcfilelists_script_path):
+        (_get_root_dir):
+        (get_opensource_dir):
+        (get_build_scripts_dir):
+        (get_extract_dependencies_from_makefile_script):
+        (get_xcode_built_products_dir):
+        (_getenv):
+        * Scripts/webkitpy/generate_xcfilelists_lib/generators.py: Added.
+        (BaseGenerator):
+        (BaseGenerator.__init__):
+        (BaseGenerator.__str__):
+        (BaseGenerator.generate):
+        (BaseGenerator._sublaunch_under_xcode):
+        (BaseGenerator.subgenerate):
+        (BaseGenerator.merge):
+        (BaseGenerator.pickle_to_file):
+        (BaseGenerator.has_action):
+        (BaseGenerator.has_error):
+        (BaseGenerator.is_valid):
+        (BaseGenerator.report_error):
+        (BaseGenerator._generate_derived):
+        (BaseGenerator._merge_derived):
+        (BaseGenerator._generate_unified):
+        (BaseGenerator._merge_unified):
+        (BaseGenerator._replace):
+        (BaseGenerator._unexpand):
+        (BaseGenerator._find_added_lines):
+        (BaseGenerator._merge_added_lines):
+        (BaseGenerator._get_file_lines):
+        (BaseGenerator._getenv):
+        (BaseGenerator._get_project_file_path):
+        (BaseGenerator._get_project_dir):
+        (BaseGenerator._get_project_file_name):
+        (BaseGenerator._get_project_name):
+        (BaseGenerator._get_sym_root):
+        (BaseGenerator._get_obj_root):
+        (BaseGenerator._get_shared_precomps_dir):
+        (BaseGenerator._get_build_dirs):
+        (BaseGenerator._get_build_dirs.define_xcode_build_dirs):
+        (BaseGenerator._get_build_dirs.define_xcode_build_dirs.read_xcode_user_default):
+        (BaseGenerator._get_build_dirs.define_command_line_build_dirs):
+        (BaseGenerator._get_derived_sources_dir):
+        (BaseGenerator._get_xcfilelist_dir):
+        (BaseGenerator._get_input_derived_xcfilelist_project_path):
+        (BaseGenerator._get_output_derived_xcfilelist_project_path):
+        (BaseGenerator._get_input_unified_xcfilelist_project_path):
+        (BaseGenerator._get_output_unified_xcfilelist_project_path):
+        (BaseGenerator._get_generate_derived_sources_script):
+        (BaseGenerator._get_generate_unified_sources_script):
+        (JavaScriptCoreGenerator):
+        (JavaScriptCoreGenerator._get_project_file_path):
+        (JavaScriptCoreGenerator._get_generate_derived_sources_script):
+        (JavaScriptCoreGenerator._get_generate_unified_sources_script):
+        (WebCoreGenerator):
+        (WebCoreGenerator._get_project_file_path):
+        (WebCoreGenerator._get_generate_derived_sources_script):
+        (WebCoreGenerator._get_generate_unified_sources_script):
+        (WebKitGenerator):
+        (WebKitGenerator._get_project_file_path):
+        (WebKitGenerator._get_derived_sources_dir):
+        (WebKitGenerator._get_generate_derived_sources_script):
+        (WebKitGenerator._get_generate_unified_sources_script):
+        (DumpRenderTreeGenerator):
+        (DumpRenderTreeGenerator._get_project_file_path):
+        (DumpRenderTreeGenerator._get_generate_derived_sources_script):
+        (WebKitTestRunnerGenerator):
+        (WebKitTestRunnerGenerator._get_project_file_path):
+        (WebKitTestRunnerGenerator._get_generate_derived_sources_script):
+        * Scripts/webkitpy/generate_xcfilelists_lib/util.py: Added.
+        (debug_log):
+        (LogEntryHelper):
+        (LogEntryHelper.__init__):
+        (LogEntryHelper.log_entry):
+        (LogEntryHelper.log_result):
+        (LogEntryHelper.log_exception):
+        (LogEntryHelper._print):
+        (LogEntryExit):
+        (LogEntryExit._show_debug_logging):
+        (LogEntryExitClass):
+        (LogEntryExitClass._show_debug_logging):
+        (LogEntryExitGlobal):
+        (LogEntryExitGlobal._show_debug_logging):
+        (subprocess_run):
+        (is_running_under_xcode):
+        (CheckValidItemAction):
+        (CheckValidItemAction.__init__):
+        (CheckValidItemAction.__call__):
+        (CheckValidItemAction.validate_item):
+        (CheckCommandAction):
+        (CheckCommandAction.__call__):
+        (InvalidCommandError):
+        (InvalidArgumentError):
+        (InvalidConfigurationError):
+        (CalledProcessError):
+        (CalledProcessError.__str__):
+        * Scripts/webkitpy/xcode/__init__.py:
+        (xcode_hash_for_path):
+        (xcode_hash_for_path.convert_to_string):
+        * Scripts/webkitpy/xcode/sdk.py: Added.
+        (SDK):
+        (SDK.__init__):
+        (SDK.__repr__):
+        (SDK.as_xcode_specification):
+        (SDK.get_preferred_sdk_for_platform):
+        (SDK._parse_sdk):
+        * Scripts/webkitpy/xcode/sdk_unittest.py: Added.
+        (SDKTest):
+
 2019-05-15  Aakash Jain  <aakash_jain@apple.com>
 
         [ews-build] Enabling uploading EWS archives to S3
diff --git a/Tools/DumpRenderTree/Scripts/check-xcfilelists.sh b/Tools/DumpRenderTree/Scripts/check-xcfilelists.sh
index 538a199..9e64e3b 100755
--- a/Tools/DumpRenderTree/Scripts/check-xcfilelists.sh
+++ b/Tools/DumpRenderTree/Scripts/check-xcfilelists.sh
@@ -8,6 +8,7 @@
 [ "${USE_INTERNAL_SDK}" == "YES" ] || { echo "### Not running because USE_INTERNAL_SDK is not YES"; exit 0; }
 
 SCRIPT="${BUILD_SCRIPTS_DIR}/generate-xcfilelists"
+[ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../../${WK_ADDITIONAL_SCRIPTS_DIR}/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../Tools/Scripts/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || { echo "### Cannot find generate-xcfilelists script"; exit 1; }
 
diff --git a/Tools/Scripts/generate-xcfilelists b/Tools/Scripts/generate-xcfilelists
index 0d86978..042a66c 100755
--- a/Tools/Scripts/generate-xcfilelists
+++ b/Tools/Scripts/generate-xcfilelists
@@ -1,6 +1,7 @@
-#!/bin/bash
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
 #
-# Copyright (C) 2018-2019 Apple Inc.  All rights reserved.
+# Copyright (C) 2019 Apple Inc.  All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
@@ -47,1330 +48,13 @@
 #
 # As part of its operation, this script can sub-launch itself under Xcode. It
 # does this in order to establish the context in which builds occur. In
-# particular, it does this in order to set needed environment variables. In
-# order to protect against environment variable name collision, all variable
-# names in this script start with "GX_".
+# particular, it does this in order to set needed environment variables.
 
+import sys
 
-function stdout()
-{
-    (( ${GX_QUIET} )) || echo "$@" >&1
-}
+from webkitpy.generate_xcfilelists_lib.application import Application
+from webkitpy.port.config import apple_additions
 
-
-function stderr()
-{
-    echo "$@" >&2
-}
-
-
-function remove_extra_spaces()
-{
-    echo $1
-}
-
-function print_option()
-{
-    local GX_OPTION="$1"
-    local GX_MESSAGE="$(remove_extra_spaces "$2")"
-
-    local GX_LINE
-    local GX_LINE_WIDTH=90
-    local GX_OPTION_WIDTH=17
-
-    if (( ${#GX_OPTION} <= GX_OPTION_WIDTH ))
-    then
-        local GX_MESSAGE_CATENATED=$(printf "  %-${GX_OPTION_WIDTH}s %s" "$GX_OPTION" "$GX_MESSAGE")
-        if (( ${#GX_MESSAGE_CATENATED} <= GX_LINE_WIDTH ))
-        then
-            stderr "${GX_MESSAGE_CATENATED}"
-            return
-        fi
-
-        local GX_MESSAGE_FIRST_LINE="${GX_MESSAGE_CATENATED:0:${GX_LINE_WIDTH}}"    # Get the first 80 characters
-        GX_MESSAGE_FIRST_LINE="${GX_MESSAGE_FIRST_LINE% *}"                         # Trim back to the last space
-        GX_MESSAGE="${GX_MESSAGE_CATENATED:${#GX_MESSAGE_FIRST_LINE}+1}"            # Get the rest after that space
-
-        stderr "${GX_MESSAGE_FIRST_LINE}"
-    else
-        stderr "  ${GX_OPTION}"
-    fi
-
-    while IFS='' read -r GX_LINE
-    do
-        GX_LINE=$(printf "  %${GX_OPTION_WIDTH}s %s" "" "$GX_LINE")
-        stderr "${GX_LINE}"
-    done < <(echo "${GX_MESSAGE}" | fold -w $(( GX_LINE_WIDTH - GX_OPTION_WIDTH - 3)) -s)
-}
-
-
-function join_by()
-{
-    local GX_DELIM=$1
-    shift
-
-    echo -n "$1"
-    shift
-
-    printf "%s" "${@/#/${GX_DELIM}}"
-}
-
-
-function usage()
-{
-    local GX_JOINED_PROJECT_TAGS=$(join_by ", " "${GX_PROJECT_TAGS[@]}")
-
-    stderr "Usage: $(basename "${GX_ME}") [OPTION...] COMMAND [PARAMETER...]"
-    stderr ""
-    stderr "Generate or check .xcfilelist files"
-    stderr ""
-    stderr "Commands:"
-    stderr ""
-    print_option "generate" "Generate a complete and up-to-date set of
-        .xcfilelist files and copy them to their appropriate places in the
-        project directories."
-    print_option "generate-xcode" "Generate .xcfilelist files for the current
-        target configuration an copy them to their appropriate places in the
-        project directories. Invoked from withing Xcode to update the current
-        build if needed."
-    print_option "check" "Generate a complete and up-to-date set of .xcfilelist
-        files and compare them to their counterparts in the project
-        directories."
-    print_option "check-xcode" "Generate .xcfilelist files for the current
-        target configuration and see if any files appear that aren't in the
-        checked-in .xcfilelist files. Invoked from within Xcode to validate the
-        current build."
-    print_option "subgenerate" "Generate an .xcfilelist file for a particular
-        combination of project, platform, and configuration. This operation is
-        performed in the context of an Xcode build in order to inherit the same
-        environment as that build."
-    print_option "help" "Print this text and exit."
-    stderr ""
-    stderr "Options:"
-    stderr ""
-    print_option "--project <project>" "Specify which project for which to
-        generate .xcfilelist files or to check. Possible values are
-        (${GX_JOINED_PROJECT_TAGS}). Default is to iterate over all projects."
-    print_option "--platform <platform>" "Specify which platform for which to
-        generate .xcfilelist files or to check. Possible values are (macosx,
-        iphoneos). Default is to iterate over all platforms, filtered to those
-        platforms that a particular project supports (e.g., you can't specify
-        'iphoneos' for WebKitTestRunner)."
-    print_option "--configuration <configuration>" "Specify which configuration
-        for which to generate .xcfilelist files or to check, Possible values
-        are (release, debug). Default is to iterate over all configurations."
-    print_option "--xcode" "Specify that existing build output can be found in
-        the directory created by the Xcode IDE (in ~/Library/Developer/Xcode)."
-    print_option "--webkitbuild" "Specify that existing build output can be
-        found in the directory used by the WebKit make files or the
-        build-webkit script (that is, in WebKitBuild or in the directory
-        identified by WEBKIT_OUTPUTDIR). This option is the default, so it
-        doesn't really get you anything by specifying this option (or by my
-        implementing it)."
-    print_option "--nocleanup" "Disable cleaning up temporary files after a
-        subgenerate operation. Normally these are cleaned up, but if
-        'subgenerate' is part of an overall 'generate' operation, then the
-        'generate' operation needs to keep around the temporary files until it
-        can complete aggregating them."
-    stderr ""
-    print_option "--dry-run" "When running through the requested process, don't
-        make any material changes. For example, for 'generate', create the new
-        .xcfilelist files, but don't copy them into their final locations"
-    print_option "--debug" "Provide verbose output."
-    print_option "--quiet" "Don't print any std output."
-    print_option "--help" "Print this text and exit."
-    stderr ""
-}
-
-
-function cleanup()
-{
-    if (( ${GX_DO_CLEANUP} )) && (( ${GX_DEFERRED_EXIT_CODE} == 0 ))
-    then
-        rm -rf "${GX_TEMP}" &> /dev/null
-    fi
-}
-
-
-function my_exit()
-{
-    local GX_ERR=$1
-    exit $GX_ERR
-}
-
-
-function die()
-{
-    local GX_ERR=$2
-    [[ "$GX_ERR" == "" ]] && GX_ERR=1
-    stderr "### (${FUNCNAME[@]}) $1"
-    my_exit $GX_ERR
-}
-
-
-function log_debug()
-{
-    (( "${GX_DEBUG}" > 0 )) && stderr "GXCF: $@"
-}
-
-
-function log_debug_var()
-{
-    local GX_VAR_NAME=$1
-    local GX_IS_ARRAY=$(declare -p ${GX_VAR_NAME} 2> /dev/null | grep -q '^declare -a' && echo 1 || echo 0)
-
-    if (( $GX_IS_ARRAY ))
-    then
-        log_debug $(printf "%-47s = (%s)" $GX_VAR_NAME "$(eval echo \$\{${GX_VAR_NAME}\[\@\]\})")
-    else
-        log_debug $(printf "%-47s = %s" $GX_VAR_NAME "$(eval echo \$\{${GX_VAR_NAME}\})")
-    fi
-}
-
-
-function log_callstack_and_parameters()
-{
-    if (( "${GX_DEBUG}" > "1" ))
-    then
-        local GX_ARGS=("$@")
-        local GX_CALLSTACK=("${FUNCNAME[@]}")
-        unset GX_CALLSTACK[0]
-        stderr "GXCF: (${GX_CALLSTACK[@]}): ${GX_ARGS[@]}"
-    fi
-}
-
-
-function log_progress()
-{
-    stdout "GXCF: $@"
-}
-
-
-function log_progress_long()
-{
-    local GX_MESSAGE="$(remove_extra_spaces "$1")"
-    local GX_LINE
-    while IFS='' read -r GX_LINE
-    do
-        log_progress $GX_LINE
-    done < <(echo "${GX_MESSAGE}" | fold -w 86 -s)
-}
-
-
-function normalize_directory_path()
-{
-    log_callstack_and_parameters "$@"
-
-    [[ -z "$1" ]] && { echo "$1"; return; }
-    cd "$1" 2> /dev/null || { echo "$1"; return; }
-    pwd -P
-}
-
-
-function normalize_file_path()
-{
-    log_callstack_and_parameters "$@"
-
-    [[ -z "$1" ]] && { echo "$1"; return; }
-    echo $(normalize_directory_path "$(dirname "$1")")/$(basename "$1")
-}
-
-
-function call()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_FN="$1"
-    [[ "$(type -t ${GX_FN})" == "function" ]] || return $?
-    eval "${GX_FN}"
-}
-
-
-function set_project_specific_settings_for_JavaScriptCore()
-{
-    log_callstack_and_parameters "$@"
-
-    GX_PS_PROJECT_FILE_PATH="${GX_OPENSOURCE_DIR}/Source/JavaScriptCore/JavaScriptCore.xcodeproj" # Can't use PROJECT_FILE_PATH because this is used pre-Xcode.
-    GX_PS_DERIVEDSOURCES_GENERATOR_RELATIVE_PATH="Scripts/generate-derived-sources.sh"
-    GX_PS_UNIFIEDSOURCES_GENERATOR_RELATIVE_PATH="Scripts/generate-unified-sources.sh"
-    GX_PS_PLATFORM_NAMES=(macosx iphoneos)
-}
-
-
-function set_project_specific_settings_for_WebCore()
-{
-    log_callstack_and_parameters "$@"
-
-    GX_PS_PROJECT_FILE_PATH="${GX_OPENSOURCE_DIR}/Source/WebCore/WebCore.xcodeproj" # Can't use PROJECT_FILE_PATH because this is used pre-Xcode.
-    GX_PS_DERIVEDSOURCES_GENERATOR_RELATIVE_PATH="Scripts/generate-derived-sources.sh"
-    GX_PS_UNIFIEDSOURCES_GENERATOR_RELATIVE_PATH="Scripts/generate-unified-sources.sh"
-    GX_PS_PLATFORM_NAMES=(macosx iphoneos)
-}
-
-
-function set_project_specific_settings_for_WebKit()
-{
-    log_callstack_and_parameters "$@"
-
-    GX_PS_PROJECT_FILE_PATH="${GX_OPENSOURCE_DIR}/Source/WebKit/WebKit.xcodeproj" # Can't use PROJECT_FILE_PATH because this is used pre-Xcode.
-    GX_PS_DERIVED_SOURCES_DIR="${BUILT_PRODUCTS_DIR}/DerivedSources/WebKit2"
-    GX_PS_DERIVEDSOURCES_GENERATOR_RELATIVE_PATH="Scripts/generate-derived-sources.sh"
-    GX_PS_UNIFIEDSOURCES_GENERATOR_RELATIVE_PATH="Scripts/generate-unified-sources.sh"
-    GX_PS_PLATFORM_NAMES=(macosx iphoneos)
-}
-
-
-function set_project_specific_settings_for_DumpRenderTree()
-{
-    log_callstack_and_parameters "$@"
-
-    GX_PS_PROJECT_FILE_PATH="${GX_OPENSOURCE_DIR}/Tools/DumpRenderTree/DumpRenderTree.xcodeproj" # Can't use PROJECT_FILE_PATH because this is used pre-Xcode.
-    GX_PS_DERIVEDSOURCES_GENERATOR_RELATIVE_PATH="Scripts/generate-derived-sources.sh"
-    GX_PS_PLATFORM_NAMES=(macosx)
-}
-
-
-function set_project_specific_settings_for_WebKitTestRunner()
-{
-    log_callstack_and_parameters "$@"
-
-    GX_PS_PROJECT_FILE_PATH="${GX_OPENSOURCE_DIR}/Tools/WebKitTestRunner/WebKitTestRunner.xcodeproj" # Can't use PROJECT_FILE_PATH because this is used pre-Xcode.
-    GX_PS_DERIVEDSOURCES_GENERATOR_RELATIVE_PATH="Scripts/generate-derived-sources.sh"
-    GX_PS_PLATFORM_NAMES=(macosx)
-}
-
-
-function set_project_specific_settings()
-{
-    log_callstack_and_parameters "$@"
-
-    # Unset the variables that the set_project_specific_settings_for_FOO
-    # functions set. We need to do this in case the function for project BAR
-    # doesn't define one or more of them, causing it to inherit the settings
-    # for a previous project FOO.
-    #
-    # To achieve this unsetting, we prefix all the variables we want to unset
-    # with "GX_PS_" ("PS for "project specific"). We can then gather all
-    # variables that start with this prefix and unset them.
-
-    unset ${!GX_PS_*}
-
-    [[ -n "${GX_PROJECT_TAG}" ]] || die "GX_PROJECT_TAG is not defined."
-
-    call set_project_specific_settings_for_${GX_PROJECT_TAG} || die "Could not set build variables for ${GX_PROJECT_TAG}."
-}
-
-
-function set_common_project_settings()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_EFFECTIVE_PROJECT_FILE_PATH="${GX_PS_PROJECT_FILE_PATH}"
-    local GX_EFFECTIVE_PROJECT_DIR=$(dirname "${GX_EFFECTIVE_PROJECT_FILE_PATH}")
-
-    [[ -n "${GX_EFFECTIVE_PROJECT_FILE_PATH}" ]] || die "GX_EFFECTIVE_PROJECT_FILE_PATH is not defined."
-    [[ -d "${GX_EFFECTIVE_PROJECT_FILE_PATH}" ]] || die "${GX_EFFECTIVE_PROJECT_FILE_PATH} is not a directory."
-    [[ -n "${GX_EFFECTIVE_PROJECT_DIR}" ]] || die "GX_EFFECTIVE_PROJECT_DIR is not defined."
-    [[ -d "${GX_EFFECTIVE_PROJECT_DIR}" ]] || die "${GX_EFFECTIVE_PROJECT_DIR} is not a directory."
-
-    # Get the paths to the scripts that drive the generation of the
-    # .xcfilelists or the data going into the .xcfilelists.
-
-    GX_DERIVEDSOURCES_GENERATOR="${GX_PS_DERIVEDSOURCES_GENERATOR_RELATIVE_PATH:+${GX_EFFECTIVE_PROJECT_DIR}/${GX_PS_DERIVEDSOURCES_GENERATOR_RELATIVE_PATH}}"
-    GX_UNIFIEDSOURCES_GENERATOR="${GX_PS_UNIFIEDSOURCES_GENERATOR_RELATIVE_PATH:+${GX_EFFECTIVE_PROJECT_DIR}/${GX_PS_UNIFIEDSOURCES_GENERATOR_RELATIVE_PATH}}"
-
-    [[ -n "${GX_DERIVEDSOURCES_GENERATOR}" ]] && { [[ -f "${GX_DERIVEDSOURCES_GENERATOR}" ]] || die "${GX_DERIVEDSOURCES_GENERATOR} does not exist."; }
-    [[ -n "${GX_UNIFIEDSOURCES_GENERATOR}" ]] && { [[ -f "${GX_UNIFIEDSOURCES_GENERATOR}" ]] || die "${GX_UNIFIEDSOURCES_GENERATOR} does not exist."; }
-
-    # Get the paths to the locations of the final .xcfilelist files.
-
-    local GX_BASE_PATH="${GX_EFFECTIVE_PROJECT_DIR}/${GX_PS_XCFILELIST_RELATIVE_PATH}"
-    GX_INPUT_DERIVED_XCFILELIST_PROJECT_PATH="${GX_BASE_PATH}/DerivedSources-input.xcfilelist"
-    GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_PATH="${GX_BASE_PATH}/DerivedSources-output.xcfilelist"
-    GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_PATH="${GX_BASE_PATH}/UnifiedSources-output.xcfilelist"
-
-    # Get the paths to the locations of the temporary .xcfilelist files (the
-    # ones being built up before being moved to their final locations).
-
-    GX_INPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH="${GX_TEMP}/${GX_INPUT_DERIVED_XCFILELIST_PROJECT_PATH}"
-    GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH="${GX_TEMP}/${GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_PATH}"
-    GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_TEMP_PATH="${GX_TEMP}/${GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_PATH}"
-
-    # Collect the default per-project commands to execute during the generate,
-    # merge, and compare stages.
-
-    GX_SUBGENERATE_ACTIONS=()
-    GX_MERGE_ACTIONS=()
-    GX_CHECK_ACTIONS=()
-
-    if [[ -n "${GX_DERIVEDSOURCES_GENERATOR}" ]]
-    then
-        GX_SUBGENERATE_ACTIONS+=(generate_derivedsources_xcfilelists)
-        GX_MERGE_ACTIONS+=(merge_derivedsources_xcfilelists)
-        GX_CHECK_ACTIONS+=(check_derivedsources_xcfilelists)
-    fi
-
-    if [[ -n "${GX_UNIFIEDSOURCES_GENERATOR}" ]]
-    then
-        GX_SUBGENERATE_ACTIONS+=(generate_unifiedsources_xcfilelists)
-        GX_MERGE_ACTIONS+=(merge_unifiedsources_xcfilelists)
-        GX_CHECK_ACTIONS+=(check_unifiedsources_xcfilelists)
-    fi
-
-    [[ -z "${GX_PS_DERIVED_SOURCES_DIR}" ]] && GX_PS_DERIVED_SOURCES_DIR="${BUILT_PRODUCTS_DIR}/DerivedSources/${PROJECT_NAME}"
-
-    GX_TEMP_INPUT_XCFILELIST="${GX_TEMP}/input.xcfilelist"
-    GX_TEMP_OUTPUT_XCFILELIST="${GX_TEMP}/output.xcfilelist"
-}
-
-
-function dump_project_settings()
-{
-    log_callstack_and_parameters "$@"
-
-    log_debug_var BUILD_SCRIPTS_DIR
-    log_debug_var BUILT_PRODUCTS_DIR
-    log_debug_var CONFIGURATION
-    log_debug_var DERIVED_SOURCES_DIR
-    log_debug_var JAVASCRIPTCORE_PRIVATE_HEADERS_DIR
-    log_debug_var PROJECT_DIR
-    log_debug_var PROJECT_FILE_PATH
-    log_debug_var PROJECT_NAME
-    log_debug_var WEBCORE_PRIVATE_HEADERS_DIR
-    log_debug_var WEBKIT2_PRIVATE_HEADERS_DIR
-    log_debug
-    log_debug_var GX_PS_PROJECT_FILE_PATH
-    log_debug_var GX_PS_DERIVEDSOURCES_GENERATOR_RELATIVE_PATH
-    log_debug_var GX_PS_UNIFIEDSOURCES_GENERATOR_RELATIVE_PATH
-    log_debug_var GX_PS_XCFILELIST_RELATIVE_PATH
-    log_debug_var GX_PS_PLATFORM_NAMES
-    log_debug
-    log_debug_var GX_PROJECT_TAG
-    log_debug_var GX_PLATFORM_NAME
-    log_debug_var GX_CONFIGURATION
-    log_debug
-    log_debug_var GX_EFFECTIVE_PROJECT_FILE_PATH
-    log_debug_var GX_EFFECTIVE_PROJECT_DIR
-    log_debug
-    log_debug_var GX_DERIVEDSOURCES_GENERATOR
-    log_debug_var GX_UNIFIEDSOURCES_GENERATOR
-    log_debug
-    log_debug_var GX_INPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH
-    log_debug_var GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH
-    log_debug_var GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_TEMP_PATH
-    log_debug
-    log_debug_var GX_INPUT_DERIVED_XCFILELIST_PROJECT_PATH
-    log_debug_var GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_PATH
-    log_debug_var GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_PATH
-    log_debug
-    log_debug_var GX_PS_DERIVED_SOURCES_DIR
-    log_debug
-    log_debug_var GX_SUBGENERATE_ACTIONS
-    log_debug_var GX_MERGE_ACTIONS
-    log_debug_var GX_CHECK_ACTIONS
-}
-
-
-function set_project_settings()
-{
-    log_callstack_and_parameters "$@"
-
-    [[ -z "${GX_PROJECT_TAG}" ]] && return
-
-    set_project_specific_settings
-    set_common_project_settings
-    dump_project_settings
-}
-
-
-function ensure_directories_exist()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_DIR
-    for GX_DIR in "$@"
-    do
-        log_debug "Creating ${GX_DIR}"
-        mkdir -p "${GX_DIR}" &> /dev/null || die "Unable to create "${GX_DIR}"."
-    done
-}
-
-
-function create_empty_files()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_FILE
-    for GX_FILE in "$@"
-    do
-        ensure_directories_exist "$(dirname "${GX_FILE}")"
-
-        log_debug "Creating ${GX_FILE}"
-        echo -n '' > "${GX_FILE}"
-    done
-}
-
-
-function append_xcfilelist_header()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_FILE
-    for GX_FILE in "$@"
-    do
-        echo '# This file is generated by the generate-xcfilelists script.' >> "${GX_FILE}"
-    done
-}
-
-
-function sort_and_unique_in_place()
-{
-    sort -u "$1" -o "$1"
-}
-
-
-function replace()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_FILE="$1"
-    local GX_PATTERN="$2"
-    local GX_REPLACEMENT="$3"
-
-    [[ -n "${GX_FILE}" ]] || die "GX_FILE is not defined."
-    [[ -f "${GX_FILE}" ]] || die "${GX_FILE} does not exist."
-
-    sed -E -e "s|${GX_PATTERN}|${GX_REPLACEMENT}|" -i '' "${GX_FILE}"
-}
-
-
-function unexpand()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_FILE="$1"
-    local GX_VAR="$2"
-    local GX_VALUE=$(eval echo \$${GX_VAR})
-
-    [[ -n "${GX_VALUE}" ]] && replace "${GX_FILE}" "^${GX_VALUE}/" "\$\($GX_VAR\)/"
-}
-
-
-function find_additions()
-{
-    # Find additions and removals so that we can report them.
-    #
-    # UPDATE: We can't really report removals. It's possible -- even
-    # overwhelmingly likely -- that we are generating .xcfilelist information
-    # for only a subset of the possible configurations for which we build. For
-    # example, a developer may be building for macOS and iOS, but not watchOS.
-    # In situations like this, we'll be generating the .xcfilelist for those
-    # two platforms, but any files specific to watchOS will not be discovered
-    # and won't be included in the .xcfilelists. If we were to report those
-    # watchOS files as files that should be removed from the .xcfilelists, then
-    # the watchOS build may fail. So, for now, let any obsolete files
-    # accumulate in the .xcfilelist files; they're mostly harmless.
-
-    local GX_NEW="$1"
-    local GX_ORIG="$2"
-    local GX_ADDITIONS="$3"
-
-    [[ -f "${GX_NEW}" ]] || die "${GX_NEW} does not exist."
-    [[ -f "${GX_ORIG}" ]] || die "${GX_ORIG} does not exist."
-
-    comm -2 -3 <(sort "${GX_NEW}") <(sort "${GX_ORIG}") > "${GX_ADDITIONS}"
-}
-
-
-function get_sdks()
-{
-    log_callstack_and_parameters "$@"
-
-    (( ${#GX_SDKS[@]} )) && return
-
-    GX_SDKS=($(
-        xcodebuild -showsdks \
-        | grep -e '\s-sdk\s' \
-        | sed -E \
-            -e 's/.*-sdk ([^[:digit:]]+)$/\1/' \
-            -e 's/.*-sdk ([^[:digit:]]+)([[:digit:]\.]+)$/\1/' \
-            -e 's/.*-sdk ([^[:digit:]]+)([[:digit:]\.]+)([^[:digit:]]+)$/\1.\3/' \
-        | sort -u
-    ))
-
-    (( ${#GX_SDKS[@]} )) || die "Unable to find any SDKs."
-}
-
-
-function get_canonical_configuration()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_PROVISIONAL_CONFIGURATION=$(echo "$1" | tr '[:upper:]' '[:lower:]')
-    local GX_RESULT=$2
-
-    [[ "${GX_PROVISIONAL_CONFIGURATION}" == "" ]]           && { eval $GX_RESULT=""; return; }
-
-    [[ "${GX_PROVISIONAL_CONFIGURATION}" == "debug" ]]      && { eval $GX_RESULT="Debug"; return; }
-    [[ "${GX_PROVISIONAL_CONFIGURATION}" == "release" ]]    && { eval $GX_RESULT="Release"; return; }
-    [[ "${GX_PROVISIONAL_CONFIGURATION}" == "production" ]] && { eval $GX_RESULT="Production"; return; }
-    [[ "${GX_PROVISIONAL_CONFIGURATION}" == "profiling" ]]  && { eval $GX_RESULT="Profiling"; return; }
-
-    die "Unrecognized configuration: $1"
-}
-
-
-function get_canonical_platform_name()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_PROVISIONAL_PLATFORM_NAME=$(echo "$1" | tr '[:upper:]' '[:lower:]')
-    local GX_RESULT=$2
-
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "" ]]                   && { eval $GX_RESULT=""; return; }
-
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "ios" ]]                && { eval $GX_RESULT="iphoneos"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "iphone" ]]             && { eval $GX_RESULT="iphoneos"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "ipad" ]]               && { eval $GX_RESULT="iphoneos"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "iphoneos" ]]           && { eval $GX_RESULT="iphoneos"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "iphonesimulator" ]]    && { eval $GX_RESULT="iphonesimulator"; return; }
-
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "mac" ]]                && { eval $GX_RESULT="macosx"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "osx" ]]                && { eval $GX_RESULT="macosx"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "macos" ]]              && { eval $GX_RESULT="macosx"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "macosx" ]]             && { eval $GX_RESULT="macosx"; return; }
-
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "tvos" ]]               && { eval $GX_RESULT="appletvos"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "appletvos" ]]          && { eval $GX_RESULT="appletvos"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "tvsimulator" ]]        && { eval $GX_RESULT="appletvsimulator"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "appletvsimulator" ]]   && { eval $GX_RESULT="appletvsimulator"; return; }
-
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "watchos" ]]            && { eval $GX_RESULT="watchos"; return; }
-    [[ "${GX_PROVISIONAL_PLATFORM_NAME}" == "watchsimulator" ]]     && { eval $GX_RESULT="watchsimulator"; return; }
-
-    die "Unrecognized platform name: $1"
-}
-
-
-function get_sdk_name()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_SDK=$1
-    local GX_RESULT=$2
-    get_canonical_platform_name "${GX_SDK}" GX_SDK
-    local GX_INTERNAL_SDK="${GX_SDK}.internal"
-
-    get_sdks
-
-    # Prefer an internal SDK if one exists.
-
-    [[ " ${GX_SDKS[@]} " =~ " ${GX_INTERNAL_SDK} " ]]   && { eval $GX_RESULT="${GX_INTERNAL_SDK}"; return; }
-    [[ " ${GX_SDKS[@]} " =~ " ${GX_SDK} " ]]            && { eval $GX_RESULT="${GX_SDK}"; return; }
-
-    die "Unsupported SDK: ${GX_SDK}."
-}
-
-
-function invoke_each_action()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_ACTION
-    for GX_ACTION in "$@"
-    do
-        eval "${GX_ACTION}"
-    done
-}
-
-
-function for_each_configuration()
-{
-    log_callstack_and_parameters "$@"
-
-    if [[ -z "${GX_CONFIGURATION}" ]]
-    then
-        for GX_CONFIGURATION in "${GX_CONFIGURATIONS[@]}"
-        do
-            eval "$@"
-        done
-
-        GX_CONFIGURATION=
-    else
-        eval "$@"
-    fi
-}
-
-
-function for_each_platform()
-{
-    log_callstack_and_parameters "$@"
-
-    if [[ -z "${GX_PLATFORM_NAME}" ]]
-    then
-        for GX_PLATFORM_NAME in "${GX_PS_PLATFORM_NAMES[@]}"
-        do
-            eval "$@"
-        done
-
-        GX_PLATFORM_NAME=
-    else
-        eval "$@"
-    fi
-}
-
-
-function for_each_project()
-{
-    log_callstack_and_parameters "$@"
-
-    if [[ -z "${GX_PROJECT_TAG}" ]]
-    then
-        for GX_PROJECT_TAG in "${GX_PROJECT_TAGS[@]}"
-        do
-            set_project_settings
-            eval "$@"
-        done
-
-        GX_PROJECT_TAG=
-    else
-        set_project_settings
-        eval "$@"
-    fi
-}
-
-
-function generate_derivedsources_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    create_empty_files "${GX_TEMP_INPUT_XCFILELIST}" "${GX_TEMP_OUTPUT_XCFILELIST}"
-
-    local GX_DERIVEDSOURCES_EXTRACTOR="${GX_HERE}/extract-dependencies-from-makefile"
-
-    [[ -n "${GX_DERIVEDSOURCES_GENERATOR}" ]] || die "GX_DERIVEDSOURCES_GENERATOR is not defined."
-    [[ -x "${GX_DERIVEDSOURCES_GENERATOR}" ]] || die "${GX_DERIVEDSOURCES_GENERATOR} does not exist or is not executable."
-    [[ -x "${GX_DERIVEDSOURCES_EXTRACTOR}" ]] || die "${GX_DERIVEDSOURCES_EXTRACTOR} does not exist or is not executable."
-
-    log_debug "Creating derived .xcfilelists for ${PROJECT_NAME}/${PLATFORM_NAME}/${CONFIGURATION}"
-
-    "${GX_DERIVEDSOURCES_GENERATOR}" \
-        NO_SUPPLEMENTAL_FILES=1 \
-        --no-builtin-rules \
-        --dry-run \
-        --always-make \
-        --debug=abvijm all \
-        1> "${GX_TEMP}/std.out" 2> "${GX_TEMP}/std.err"
-    local GX_RESULT=$?
-
-    if (( ${GX_RESULT} ))
-    then
-        sed -E -e 's/^/GXCF: /' < "${GX_TEMP}/std.err"
-        die "Error generating derived sources: error = ${GX_RESULT}" ${GX_RESULT}
-    fi
-
-    cat "${GX_TEMP}/std.out" \
-    | "${GX_DERIVEDSOURCES_EXTRACTOR}" \
-        --input "${GX_TEMP_INPUT_XCFILELIST}" \
-        --output "${GX_TEMP_OUTPUT_XCFILELIST}"
-    local GX_RESULT=$?
-
-    (( ${GX_RESULT} )) && die "Error extracting dependencies from DerivedSources.make: error = ${GX_RESULT}"
-    [[ -f "${GX_TEMP_INPUT_XCFILELIST}" ]] || die "${GX_TEMP_INPUT_XCFILELIST} was not generated."
-    [[ -f "${GX_TEMP_OUTPUT_XCFILELIST}" ]] || die "${GX_TEMP_OUTPUT_XCFILELIST} was not generated."
-
-    replace "${GX_TEMP_INPUT_XCFILELIST}" '^WebCore/'                      '$(PROJECT_DIR)/'
-    replace "${GX_TEMP_INPUT_XCFILELIST}" '^JavaScriptCore/'               '$(PROJECT_DIR)/'
-    replace "${GX_TEMP_INPUT_XCFILELIST}" '^JavaScriptCorePrivateHeaders/' '$(JAVASCRIPTCORE_PRIVATE_HEADERS_DIR)/'
-    replace "${GX_TEMP_INPUT_XCFILELIST}" '^WebKit2PrivateHeaders/'        '$(WEBKIT2_PRIVATE_HEADERS_DIR)/'
-    unexpand "${GX_TEMP_INPUT_XCFILELIST}" PROJECT_DIR
-    unexpand "${GX_TEMP_INPUT_XCFILELIST}" WEBKITADDITIONS_HEADERS_FOLDER_PATH
-    unexpand "${GX_TEMP_INPUT_XCFILELIST}" WEBCORE_PRIVATE_HEADERS_DIR
-    unexpand "${GX_TEMP_INPUT_XCFILELIST}" WEBKIT2_PRIVATE_HEADERS_DIR
-    unexpand "${GX_TEMP_INPUT_XCFILELIST}" JAVASCRIPTCORE_PRIVATE_HEADERS_DIR
-    unexpand "${GX_TEMP_INPUT_XCFILELIST}" BUILT_PRODUCTS_DIR
-
-    replace "${GX_TEMP_OUTPUT_XCFILELIST}" "^" "${GX_PS_DERIVED_SOURCES_DIR}/"
-    unexpand "${GX_TEMP_OUTPUT_XCFILELIST}" BUILT_PRODUCTS_DIR
-
-    merge_xcfilelists_helper "${GX_TEMP_INPUT_XCFILELIST}" "${GX_INPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH}"
-    merge_xcfilelists_helper "${GX_TEMP_OUTPUT_XCFILELIST}" "${GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH}"
-}
-
-
-function generate_unifiedsources_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    create_empty_files "${GX_TEMP_OUTPUT_XCFILELIST}"
-
-    [[ -n "${GX_UNIFIEDSOURCES_GENERATOR}" ]] || die "GX_UNIFIEDSOURCES_GENERATOR is not defined."
-    [[ -x "${GX_UNIFIEDSOURCES_GENERATOR}" ]] || die "${GX_UNIFIEDSOURCES_GENERATOR} does not exist or is not executable."
-
-    local GX_BUILD_SCRIPTS_DIR="${GX_OPENSOURCE_DIR}/Source/WTF/Scripts"
-    [[ -d "${GX_BUILD_SCRIPTS_DIR}" ]] || die "${GX_BUILD_SCRIPTS_DIR} does not exist or is not a directory."
-    [[ -f "${GX_BUILD_SCRIPTS_DIR}/generate-unified-source-bundles.rb" ]] || die "${GX_BUILD_SCRIPTS_DIR}/generate-unified-source-bundles.rb does not exist or is not a file."
-
-    log_debug "Creating unified .xcfilelists for ${PROJECT_NAME}/${PLATFORM_NAME}/${CONFIGURATION}"
-
-    BUILD_SCRIPTS_DIR="${GX_BUILD_SCRIPTS_DIR}" \
-    "${GX_UNIFIEDSOURCES_GENERATOR}" \
-        --generate-xcfilelists \
-        --output-xcfilelist-path "${GX_TEMP_OUTPUT_XCFILELIST}"
-    GX_RESULT=$?
-
-    (( ${GX_RESULT} )) && die "Error generating unified sources: error = ${GX_RESULT}"
-    [[ -f "${GX_TEMP_OUTPUT_XCFILELIST}" ]] || die "${GX_TEMP_OUTPUT_XCFILELIST} was not generated."
-
-    unexpand "${GX_TEMP_OUTPUT_XCFILELIST}" BUILT_PRODUCTS_DIR
-
-    merge_xcfilelists_helper "${GX_TEMP_OUTPUT_XCFILELIST}" "${GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_TEMP_PATH}"
-}
-
-
-function subgenerate_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    invoke_each_action "${GX_SUBGENERATE_ACTIONS[@]}"
-}
-
-
-function sublaunch_under_xcode()
-{
-    log_callstack_and_parameters "$@"
-
-    # Sublaunch the script for the given project, for each platform for which
-    # the project is built, and for Debug and Release configurations.
-
-    local GX_ARGS=("$@")
-    (( ${GX_DRY_RUN} )) && GX_ARGS+=("--dry-run")
-    (( ${GX_DEBUG} )) && { for n in $(seq $GX_DEBUG); do GX_ARGS+=("--debug"); done; }
-    (( ${GX_QUIET} )) && GX_ARGS+=("--quiet")
-
-    local GX_SDK_NAME
-    get_sdk_name "${GX_PLATFORM_NAME}" GX_SDK_NAME
-
-    log_debug "Sublaunching for: ${GX_PROJECT_TAG}/${GX_PLATFORM_NAME}/${GX_CONFIGURATION}"
-
-    local GX_XCODE_PARAMETERS=(
-        -project "${GX_PS_PROJECT_FILE_PATH}"
-        -sdk "${GX_SDK_NAME}"
-        -configuration "${GX_CONFIGURATION}"
-        -target "Apply Configuration to XCFileLists"
-    )
-
-    if (( ${GX_USE_WEBKITBUILD_BUILD_OUTPUT} ))
-    then
-        local GX_WEBKITBUILD_DIR="${WEBKIT_OUTPUTDIR:-${GX_OPENSOURCE_DIR}/WebKitBuild}"
-        [[ -d "${GX_WEBKITBUILD_DIR}" ]] || die "${GX_WEBKITBUILD_DIR} does not exist."
-
-        GX_XCODE_PARAMETERS+=(
-            SYMROOT="${GX_WEBKITBUILD_DIR}"
-            OBJROOT="${GX_WEBKITBUILD_DIR}"
-            SHARED_PRECOMPS_DIR="${GX_WEBKITBUILD_DIR}/PrecompiledHeaders"
-        )
-    fi
-
-    if (( $GX_DEBUG > 0 ))
-    then
-        WK_SUBLAUNCH_SCRIPT_PARAMETERS=("${GX_ARGS[@]}") xcodebuild "${GX_XCODE_PARAMETERS[@]}"
-    else
-        WK_SUBLAUNCH_SCRIPT_PARAMETERS=("${GX_ARGS[@]}") xcodebuild "${GX_XCODE_PARAMETERS[@]}" | grep '^\.\.\. '
-    fi
-
-    local GX_RESULT=${PIPESTATUS[0]}
-    (( ${GX_RESULT} )) && die "Error sub-launching under xcode: error = ${GX_RESULT}"
-}
-
-
-function reset_project_specific_temp_files()
-{
-    log_callstack_and_parameters "$@"
-
-    create_empty_files \
-        "${GX_INPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH}" "${GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH}" \
-        "${GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_TEMP_PATH}"
-}
-
-
-function generate_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    reset_project_specific_temp_files
-
-    for_each_platform \
-        for_each_configuration \
-            sublaunch_under_xcode \
-                "${GX_SUBEXECUTE_SCRIPT}" subgenerate --nocleanup --project "${GX_PROJECT_TAG}"
-}
-
-
-function merge_xcfilelists_helper()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_SOURCE="$1"
-    local GX_DEST="$2"
-    local GX_ADDITIONS="${GX_TEMP}/diff_added.tmp"
-
-    append_xcfilelist_header "${GX_SOURCE}"
-    sort_and_unique_in_place "${GX_SOURCE}"
-
-    find_additions "${GX_SOURCE}" "${GX_DEST}" "${GX_ADDITIONS}"
-
-    if [[ -s "${GX_ADDITIONS}" ]]
-    then
-        cat "${GX_SOURCE}" >> "${GX_DEST}"
-        sort_and_unique_in_place "${GX_DEST}"
-        return 0
-    fi
-
-    return 1
-}
-
-
-function merge_derivedsources_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    log_debug "Merging ${GX_INPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH} into ${GX_INPUT_DERIVED_XCFILELIST_PROJECT_PATH}"
-    log_debug "Merging ${GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH} into ${GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_PATH}"
-
-    if (( ! ${GX_DRY_RUN} ))
-    then
-        merge_xcfilelists_helper "${GX_INPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH}" "${GX_INPUT_DERIVED_XCFILELIST_PROJECT_PATH}" && GX_DEFERRED_EXIT_CODE=3
-        log_debug "GX_DEFERRED_EXIT_CODE = $GX_DEFERRED_EXIT_CODE"
-
-        merge_xcfilelists_helper "${GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH}" "${GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_PATH}" && GX_DEFERRED_EXIT_CODE=3
-        log_debug "GX_DEFERRED_EXIT_CODE = $GX_DEFERRED_EXIT_CODE"
-    fi
-}
-
-
-function merge_unifiedsources_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    log_debug "Merging ${GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_TEMP_PATH} into ${GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_PATH}"
-
-    if (( ! ${GX_DRY_RUN} ))
-    then
-        merge_xcfilelists_helper "${GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_TEMP_PATH}" "${GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_PATH}" && GX_DEFERRED_EXIT_CODE=3
-        log_debug "GX_DEFERRED_EXIT_CODE = $GX_DEFERRED_EXIT_CODE"
-    fi
-}
-
-
-function merge_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    invoke_each_action "${GX_MERGE_ACTIONS[@]}"
-
-    log_debug "GX_DEFERRED_EXIT_CODE = $GX_DEFERRED_EXIT_CODE"
-}
-
-
-function check_xcfilelists_helper()
-{
-    log_callstack_and_parameters "$@"
-
-    local GX_NEW="$1"
-    local GX_ORIG="$2"
-    local GX_ADDITIONS="${GX_TEMP}/diff_added.tmp"
-
-    log_debug "Checking ${GX_NEW} against ${GX_ORIG}"
-
-    find_additions "${GX_NEW}" "${GX_ORIG}" "${GX_ADDITIONS}"
-
-    if [[ -s "${GX_ADDITIONS}" ]]
-    then
-        log_progress
-        log_progress "------------------------------------------------------------------------------"
-        log_progress "Found added files for ${GX_ORIG}:"
-        log_progress "------------------------------------------------------------------------------"
-
-        local GX_LINE
-        while IFS='' read -r GX_LINE
-        do
-            log_progress "${GX_LINE}"
-        done < "${GX_ADDITIONS}"
-
-        log_progress "------------------------------------------------------------------------------"
-
-        GX_DEFERRED_EXIT_CODE=2
-    fi
-}
-
-
-function check_derivedsources_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    check_xcfilelists_helper "${GX_INPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH}" "${GX_INPUT_DERIVED_XCFILELIST_PROJECT_PATH}"
-    check_xcfilelists_helper "${GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_TEMP_PATH}" "${GX_OUTPUT_DERIVED_XCFILELIST_PROJECT_PATH}"
-}
-
-
-function check_unifiedsources_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    check_xcfilelists_helper "${GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_TEMP_PATH}" "${GX_OUTPUT_UNIFIED_XCFILELIST_PROJECT_PATH}"
-}
-
-
-function check_xcfilelists()
-{
-    log_callstack_and_parameters "$@"
-
-    invoke_each_action "${GX_CHECK_ACTIONS[@]}"
-}
-
-
-function report_merge_results()
-{
-    log_callstack_and_parameters "$@"
-
-    log_debug "GX_DEFERRED_EXIT_CODE = $GX_DEFERRED_EXIT_CODE"
-
-    if (( ${GX_DEFERRED_EXIT_CODE} ))
-    then
-        log_progress
-
-        local GX_MESSAGE='".xcfilelist" files tell the build system what files
-            are consumed and produced by the "Run Script" build phases in
-            Xcode. At least one of these .xcfilelist files was out of date and
-            has been updated. You now need to restart your build.'
-
-        log_progress_long "${GX_MESSAGE}"
-    fi
-}
-
-
-function report_remediation_steps()
-{
-    log_callstack_and_parameters "$@"
-
-    if (( ${GX_DEFERRED_EXIT_CODE} ))
-    then
-        log_progress
-
-        # We can either be called from within an xcodebuild context (meaning
-        # that we are being called during a build to validate the .xcfilelists
-        # for the current build configuration) or from the command line (to
-        # validate all .xcfilelists). We'll determine which of these is the
-        # case by checking $GX_PROJECT_TAG (which will have been set via the
-        # --project <TAG> option passed in to us when we're invoked in this
-        # context).
-        #
-        # Further, if called from within xcodebuild, it's important to know if
-        # we're being called from within Xcode or being invoked by a Makefile.
-        # If the former, the output/build files we are looking for are found in
-        # ~/Library/Developer/Xcode/DerivedData. Otherwise, they'll be found in
-        # OpenSource/WebKitBuild (or whatever $WEBKIT_OUTPUTDIR points to). We
-        # need to distinguish between these so that we can tell the user how to
-        # invoke us in a way that finds the right output/build files.
-        #
-        # If invoked from the command line, we really can't tell where the
-        # output files are, so give the user advice in this area.
-
-        local GX_MESSAGE='".xcfilelist" files tell the build system what files
-            are consumed and produced by the "Run Script" build phases in
-            Xcode. At least one of these .xcfilelist files are out of date and
-            need to be regenerated. Regenerate these files by running
-            `Tools/Scripts/generate-xcfilelists generate'
-
-        if [[ -n "${GX_PROJECT_TAG}" ]]
-        then
-            local GX_MESSAGE+=" --project ${GX_PROJECT_TAG}"
-            if [[ "${SYMROOT}" =~ Library/Developer/Xcode/DerivedData ]]
-            then
-                local GX_MESSAGE+=" --xcode"
-            fi
-        else
-            if (( ${GX_USE_XCODE_BUILD_OUTPUT} ))
-            then
-                local GX_MESSAGE+=" --xcode"
-            fi
-        fi
-
-        local GX_MESSAGE+='`, or manually add the file or files shown above to
-        the indicated .xcfilelist files. Then restart your build. When
-        submitting, include the updated .xcfilelist files.'
-
-        log_progress_long "${GX_MESSAGE}"
-    fi
-}
-
-
-function do_generate()
-{
-    # Invoked from the command line to generate .xcfilelist files. Use any
-    # specified project, platform, and/or configuration. Any of those that
-    # aren't specified results in our iterating over all possible values for
-    # the unspecified value.
-
-    log_callstack_and_parameters "$@"
-
-    if [[ -z "${GX_PROJECT_TAG}" ]]
-    then
-        log_progress "=== Generating all .xcfilelists ==="
-    else
-        log_progress "=== Generating .xcfilelists for ${GX_PROJECT_TAG} ==="
-    fi
-
-    for_each_project \
-        generate_xcfilelists
-}
-
-
-function do_merge()
-{
-    # Implicitly invoked for generate and generate-xcode operations to move the
-    # temporary results into the Xcode project.
-
-    log_callstack_and_parameters "$@"
-
-    if [[ -z "${GX_PROJECT_TAG}" ]]
-    then
-        log_progress "=== Merging all .xcfilelists into place ==="
-    else
-        log_progress "=== Merging .xcfilelists for ${GX_PROJECT_TAG} ==="
-    fi
-
-    for_each_project \
-        merge_xcfilelists
-
-    log_debug "GX_DEFERRED_EXIT_CODE = $GX_DEFERRED_EXIT_CODE"
-}
-
-
-function do_check()
-{
-    # Implicitly invoked for check and check-xcode operations to check the
-    # temporary results against the Xcode project.
-
-    log_callstack_and_parameters "$@"
-
-    # Being invoked from the command-line to check everything.
-
-    if [[ -z "${GX_PROJECT_TAG}" ]]
-    then
-        log_progress "=== Checking all .xcfilelists ==="
-    else
-        log_progress "=== Checking .xcfilelists for ${GX_PROJECT_TAG} ==="
-    fi
-
-    for_each_project \
-        check_xcfilelists
-}
-
-
-function do_subgenerate()
-{
-    # Invoked from within an Xcode context to generate .xcfilelist files. Use
-    # the project, platform, an configuration established in the environment.
-
-    log_callstack_and_parameters "$@"
-
-    [[ -n "${GX_PROJECT_TAG}" ]] || die "GX_PROJECT_TAG is not defined."
-    [[ -n "${PROJECT_NAME}" ]] || die "subgenerate should only be invoked in an Xcode context."
-
-    log_progress "=== Generating .xcfilelists for ${PROJECT_NAME}/${PLATFORM_NAME}/${CONFIGURATION} ==="
-
-    set_project_settings
-
-    # We're called during generate-xcode, check-xcode, and subgenerate
-    # operations. We need to reset our project-specific temp files for the
-    # first two, but not the last one.
-
-    (( ${GX_DO_SUBGENERATE} )) || reset_project_specific_temp_files
-
-    subgenerate_xcfilelists
-}
-
-
-function main()
-{
-    log_callstack_and_parameters "$@"
-
-    log_debug_var GX_ME
-    log_debug_var GX_HERE
-    log_debug_var GX_ROOT_DIR
-    log_debug_var GX_OPENSOURCE_DIR
-    log_debug_var GX_TEMP
-    log_debug_var GX_PROJECT_TAGS
-    log_debug_var GX_CONFIGURATIONS
-    log_debug_var GX_SUBEXECUTE_SCRIPT
-    log_debug_var GX_DO_GENERATE
-    log_debug_var GX_DO_GENERATE_XCODE
-    log_debug_var GX_DO_CHECK
-    log_debug_var GX_DO_CHECK_XCODE
-    log_debug_var GX_DO_SUBGENERATE
-    log_debug_var GX_DO_CLEANUP
-    log_debug_var GX_USE_XCODE_BUILD_OUTPUT
-    log_debug_var GX_USE_WEBKITBUILD_BUILD_OUTPUT
-    log_debug_var GX_DRY_RUN
-    log_debug_var GX_DEBUG
-    log_debug_var GX_QUIET
-    log_debug_var GX_ORIG_ARGS
-
-    if (( ${GX_DO_HELP} ))
-    then
-        usage
-        my_exit 0
-    fi
-
-    if (( GX_DO_GENERATE + GX_DO_GENERATE_XCODE + GX_DO_CHECK + GX_DO_CHECK_XCODE + GX_DO_SUBGENERATE + GX_DO_HELP < 1 ))
-    then
-        stderr "### One of generate, generate-xcode, check, check-xcode, subgenerate, or --help must be specified."
-        my_exit 1
-    fi
-
-    if (( GX_DO_GENERATE + GX_DO_GENERATE_XCODE + GX_DO_CHECK + GX_DO_CHECK_XCODE + GX_DO_SUBGENERATE + GX_DO_HELP > 1 ))
-    then
-        stderr "### Only one of generate, generate-xcode, check, check-xcode, subgenerate, or --help can be specified."
-        my_exit 1
-    fi
-
-    [[ -z "${GX_PROJECT_TAG}" || ( " ${GX_PROJECT_TAGS[@]} " =~ " ${GX_PROJECT_TAG} " ) ]] || { die "Unrecognized project: ${GX_PROJECT_TAG}";  }
-    get_canonical_platform_name "${GX_PLATFORM_NAME}" GX_PLATFORM_NAME
-    get_canonical_configuration "${GX_CONFIGURATION}" GX_CONFIGURATION
-
-    if (( ${GX_DO_GENERATE} ))
-    then
-        do_generate
-        call post_generate_hook
-
-        do_merge
-        call post_merge_hook
-
-        report_merge_results
-    elif (( ${GX_DO_GENERATE_XCODE} ))
-    then
-        do_subgenerate
-        call post_generate_hook
-
-        do_merge
-        call post_merge_hook
-
-        report_merge_results
-    elif (( ${GX_DO_CHECK} ))
-    then
-        do_generate
-        call post_generate_hook
-
-        do_check
-        call post_check_hook
-
-        report_remediation_steps
-    elif (( ${GX_DO_CHECK_XCODE} ))
-    then
-        do_subgenerate
-        call post_generate_hook
-
-        do_check
-        call post_check_hook
-
-        report_remediation_steps
-    elif (( ${GX_DO_SUBGENERATE} ))
-    then
-        do_subgenerate
-    else
-        stderr "### No subcommand provided"
-        usage
-        my_exit 1
-    fi
-
-    my_exit ${GX_DEFERRED_EXIT_CODE}
-}
-
-
-# Initialize and sanity check
-
-GX_ORIG_ARGS=("$@")
-
-GX_DO_GENERATE=0
-GX_DO_GENERATE_XCODE=0
-GX_DO_CHECK=0
-GX_DO_CHECK_XCODE=0
-GX_DO_SUBGENERATE=0
-GX_DO_HELP=0
-GX_DO_CLEANUP=0
-GX_USE_XCODE_BUILD_OUTPUT=0
-GX_USE_WEBKITBUILD_BUILD_OUTPUT=1
-GX_DRY_RUN=0
-GX_DEBUG=0
-GX_QUIET=0
-
-GX_DEFERRED_EXIT_CODE=0
-GX_PROJECT_TAG=
-GX_PLATFORM_NAME=
-GX_CONFIGURATION=
-GX_SDKS=()
-
-GX_ME=$(normalize_file_path "${BASH_SOURCE[0]}")
-GX_HERE=$(dirname "${GX_ME}")
-GX_ROOT_DIR=$(normalize_directory_path "${GX_HERE}/../../..")
-GX_OPENSOURCE_DIR="${GX_ROOT_DIR}/OpenSource"
-GX_TEMP=$(normalize_directory_path /tmp/generate-xcfilelists)
-GX_PROJECT_TAGS=(JavaScriptCore WebCore WebKit DumpRenderTree WebKitTestRunner)
-GX_CONFIGURATIONS=(Release Debug)
-GX_SUBEXECUTE_SCRIPT="${GX_ME}"
-
-[[ -n "${GX_ROOT_DIR}" ]] || die "Could not find GX_ROOT_DIR."
-[[ -n "${GX_OPENSOURCE_DIR}" ]] || die "Could not find GX_OPENSOURCE_DIR."
-[[ -d "${GX_ROOT_DIR}" ]] || die "${GX_ROOT_DIR} does not exist."
-[[ -d "${GX_OPENSOURCE_DIR}" ]] || die "${GX_OPENSOURCE_DIR} does not exist."
-
-trap cleanup EXIT
-
-ensure_directories_exist "${GX_TEMP}"
-
-
-# Process command-line parameters.
-
-while [[ "${1:+x}" ]]
-do
-    case "${1}" in
-        generate)       GX_DO_GENERATE=1 ;;
-        generate-xcode) GX_DO_GENERATE_XCODE=1 ;;
-        check)          GX_DO_CHECK=1 ;;
-        check-xcode)    GX_DO_CHECK_XCODE=1 ;;
-        subgenerate)    GX_DO_SUBGENERATE=1 ;;
-        help)           GX_DO_HELP=1 ;;
-
-        --project)      shift; GX_PROJECT_TAG="$1" ;;
-        --platform)     shift; GX_PLATFORM_NAME="$1" ;;
-        --configuration)shift; GX_CONFIGURATION="$1" ;;
-        --xcode)        GX_USE_XCODE_BUILD_OUTPUT=1; GX_USE_WEBKITBUILD_BUILD_OUTPUT=0 ;;
-        --webkitbuild)  GX_USE_XCODE_BUILD_OUTPUT=0; GX_USE_WEBKITBUILD_BUILD_OUTPUT=1 ;;
-        --nocleanup)    GX_DO_CLEANUP=0 ;;
-
-        -n | --dry-run) GX_DRY_RUN=1 ;;
-        -d | --debug)   GX_DEBUG=$(( $GX_DEBUG + 1 )) ;;
-        -q | --quiet)   GX_QUIET=1 ;;
-        -h | --help)    GX_DO_HELP=1 ;;
-
-        *)              stderr "### Unknown command: $1"
-                        usage
-                        my_exit 1 ;;
-    esac
-    shift
-done
-
-
-GX_SOURCED=$([[ "$0" == "${BASH_SOURCE[@]}" ]] && echo 0 || echo 1)
-if (( ! ${GX_SOURCED} ))
-then
-    GX_INTERNAL_ME="${GX_ROOT_DIR}/Internal/Tools/Scripts/generate-xcfilelists"
-    if [[ -x "${GX_INTERNAL_ME}" ]]
-    then
-        "${GX_INTERNAL_ME}" "${GX_ORIG_ARGS[@]}"
-    else
-        main
-    fi
-fi
+if __name__ == "__main__":
+    application_class = apple_additions().get_generate_xcfilelists_application() if apple_additions() else Application
+    sys.exit(application_class(__file__).run())
diff --git a/Tools/Scripts/webkitpy/common/attribute_saver.py b/Tools/Scripts/webkitpy/common/attribute_saver.py
new file mode 100644
index 0000000..3fa7f17
--- /dev/null
+++ b/Tools/Scripts/webkitpy/common/attribute_saver.py
@@ -0,0 +1,54 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2019 Apple Inc.  All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+# OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+# Context Manager for saving the value of an object's attribute, setting it to
+# a new value (None, by default), and then restoring the original value.
+#
+# Used as:
+#
+#   myObject.fooAttribute = 1
+#   print(myObject.fooAttribute)
+#   with AttributeSaver(myObject, "fooAttribute", 5):
+#       print(myObject.fooAttribute)
+#   print(myObject.fooAttribute)
+#
+# Prints: 1, 5, 1
+
+class AttributeSaver:
+    def __init__(self, obj, attribute, value=None):
+        self.obj = obj
+        self.attribute = attribute
+        self.old_value = getattr(self.obj, self.attribute)
+        self.new_value = value
+
+    def __enter__(self):
+        setattr(self.obj, self.attribute, self.new_value)
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        setattr(self.obj, self.attribute, self.old_value)
+        return None
diff --git a/Tools/Scripts/webkitpy/common/attribute_saver_unittest.py b/Tools/Scripts/webkitpy/common/attribute_saver_unittest.py
new file mode 100644
index 0000000..86aa588
--- /dev/null
+++ b/Tools/Scripts/webkitpy/common/attribute_saver_unittest.py
@@ -0,0 +1,127 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2019 Apple Inc.  All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+# OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+import unittest
+
+from webkitpy.common.attribute_saver import AttributeSaver
+
+
+class AttributeSaverTest(unittest.TestCase):
+
+    class SimpleTestClass:
+        def __init__(self):
+            self.value = 0
+
+    def test_class(self):
+        obj = self.SimpleTestClass()
+        self.assertEquals(obj.value, 0)
+
+    def test_normal_default(self):
+        obj = self.SimpleTestClass()
+        self.assertEquals(obj.value, 0)
+        with AttributeSaver(obj, "value"):
+            self.assertEquals(obj.value, None)
+        self.assertEquals(obj.value, 0)
+
+    def test_normal_value(self):
+        obj = self.SimpleTestClass()
+        self.assertEquals(obj.value, 0)
+        with AttributeSaver(obj, "value", 1):
+            self.assertEquals(obj.value, 1)
+        self.assertEquals(obj.value, 0)
+
+    def test_normal_value_on_exception(self):
+        with self.assertRaises(RuntimeError):
+            obj = self.SimpleTestClass()
+            self.assertEquals(obj.value, 0)
+            try:
+                with AttributeSaver(obj, "value", 1):
+                    self.assertEquals(obj.value, 1)
+                    raise RuntimeError()
+            except:
+                self.assertEquals(obj.value, 0)
+                raise
+            self.assertEquals(obj.value, 0)
+
+    def test_normal_value_on_normal_exit(self):
+        obj = self.SimpleTestClass()
+        self.assertEquals(obj.value, 0)
+        try:
+            with AttributeSaver(obj, "value", 1):
+                self.assertEquals(obj.value, 1)
+        except:
+            self.assertEquals(obj.value, 0)
+            raise
+        self.assertEquals(obj.value, 0)
+
+    def test_normal_value_with_finally_on_exception(self):
+        with self.assertRaises(RuntimeError):
+            obj = self.SimpleTestClass()
+            self.assertEquals(obj.value, 0)
+            try:
+                with AttributeSaver(obj, "value", 1):
+                    self.assertEquals(obj.value, 1)
+                    raise RuntimeError()
+            finally:
+                self.assertEquals(obj.value, 0)
+            self.assertEquals(obj.value, 0)
+
+    def test_normal_value_with_finally_on_normal_exit(self):
+        obj = self.SimpleTestClass()
+        self.assertEquals(obj.value, 0)
+        try:
+            with AttributeSaver(obj, "value", 1):
+                self.assertEquals(obj.value, 1)
+        finally:
+            self.assertEquals(obj.value, 0)
+        self.assertEquals(obj.value, 0)
+
+    def test_normal_value_with_else_on_exception(self):
+        with self.assertRaises(RuntimeError):
+            obj = self.SimpleTestClass()
+            self.assertEquals(obj.value, 0)
+            try:
+                with AttributeSaver(obj, "value", 1):
+                    self.assertEquals(obj.value, 1)
+                    raise RuntimeError()
+            except IOError:
+                self.assertFalse(True)
+            else:
+                self.assertEquals(obj.value, 0)
+            self.assertEquals(obj.value, 0)
+
+    def test_normal_value_with_else_on_normal_exit(self):
+        obj = self.SimpleTestClass()
+        self.assertEquals(obj.value, 0)
+        try:
+            with AttributeSaver(obj, "value", 1):
+                self.assertEquals(obj.value, 1)
+        except IOError:
+            self.assertFalse(True)
+        else:
+            self.assertEquals(obj.value, 0)
+        self.assertEquals(obj.value, 0)
diff --git a/Tools/Scripts/webkitpy/generate_xcfilelists_lib/__init__.py b/Tools/Scripts/webkitpy/generate_xcfilelists_lib/__init__.py
new file mode 100644
index 0000000..c641b96
--- /dev/null
+++ b/Tools/Scripts/webkitpy/generate_xcfilelists_lib/__init__.py
@@ -0,0 +1,28 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2019 Apple Inc.  All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+# OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# This file is equired for Python to search this directory for module files.
diff --git a/Tools/Scripts/webkitpy/generate_xcfilelists_lib/application.py b/Tools/Scripts/webkitpy/generate_xcfilelists_lib/application.py
new file mode 100644
index 0000000..8089ace
--- /dev/null
+++ b/Tools/Scripts/webkitpy/generate_xcfilelists_lib/application.py
@@ -0,0 +1,465 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2019 Apple Inc.  All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+# OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# Application represents the main operation of the script. It's a singleton,
+# created by main() and then invoked to run everything. This class parses the
+# command-line options, validates them, creates and invokes BaseGenerators,
+# reports the results, and handles the catching and reporting of any
+# exceptions/errors.
+
+from __future__ import print_function
+
+import argparse
+import itertools
+import os
+import sys
+import textwrap
+import traceback
+
+from functools import reduce
+
+import webkitpy.generate_xcfilelists_lib.generators as Generators
+import webkitpy.generate_xcfilelists_lib.util as util
+
+
+EX_GENERAL_ERROR = 1  # General error
+EX_ACTION_REQUIRED = 2  # Returned when script determines that the generated .xcfilelist files have changed.
+
+
+class Application(object):
+
+    __slots__ = (
+        "command_file",
+        "parser", "cmd_line_args",
+        "dispatch", "project_specific_generators",
+        "supported_project_tags", "supported_platforms", "supported_configurations")
+
+    # Aliases for platforms. These are handy when using the script from the
+    # command line and you don't remember if it's "ios" or "iphoneos, or "tvos"
+    # or "appletvos". This list of aliases will let you use any of those.
+
+    platform_aliases = {
+        "ios":          "iphoneos",
+        "iphone":       "iphoneos",
+        "simulator":    "iphonesimulator",
+        "sim":          "iphonesimulator",
+        "mac":          "macosx",
+        "macos":        "macosx",
+        "osx":          "macosx",
+        "tvos":         "appletvos",
+        "tv":           "appletvos",
+        "tvsimulator":  "appletvsimulator",
+        "watch":        "watchos",
+    }
+
+    @util.LogEntryExit
+    def __init__(self, command_file):
+        self.command_file = os.path.realpath(command_file)
+        self.parser = None
+        self.cmd_line_args = None
+
+        self.dispatch = {
+            "generate":       self._cmd_set_environment_and_generate,
+            "generate-xcode": self._cmd_generate_within_xcode,
+            "check":          self._cmd_set_environment_and_check,
+            "check-xcode":    self._cmd_check_within_xcode,
+            "generate-inner": self._cmd_generate_within_xcode_and_return_results_to_caller,
+            "help":           self._cmd_help,
+        }
+
+        self.project_specific_generators = {
+            "JavaScriptCore":   Generators.JavaScriptCoreGenerator,
+            "WebCore":          Generators.WebCoreGenerator,
+            "WebKit":           Generators.WebKitGenerator,
+            "DumpRenderTree":   Generators.DumpRenderTreeGenerator,
+            "WebKitTestRunner": Generators.WebKitTestRunnerGenerator,
+        }
+
+        self.supported_project_tags = None
+        self.supported_platforms = None
+        self.supported_configurations = None
+
+    @util.LogEntryExit
+    def run(self):
+        try:
+            self._initialize()
+
+            self.parser = self._create_parser()
+            self.cmd_line_args = args = self.parser.parse_args()
+
+            if args.help:
+                return self._cmd_help(os.EX_OK)
+
+            self._validate_args(args)
+
+            try:
+                func = self.dispatch[args.command]
+            except KeyError as e:
+                raise util.InvalidCommandError(args.command)
+
+            return func()
+
+        except util.InvalidArgumentError as e:
+            print("### Invalid argument: {}".format(e))
+            return self._cmd_help(os.EX_USAGE)
+
+        except util.InvalidCommandError as e:
+            if e.args:
+                print("### Invalid command: {}".format(e))
+            else:
+                print("### Missing command")
+            return self._cmd_help(os.EX_USAGE)
+
+        except SystemExit:
+            raise
+
+        except BaseException as e:
+            traceback.print_exc()
+            return os.EX_SOFTWARE
+
+    # Perform some post __init__ initialization. This is performed after
+    # __init__ so that we can respond to any information provided in any
+    # sub-class's __init__.
+
+    @util.LogEntryExit
+    def _initialize(self):
+        def collect_attributes(key):
+            configurations = set()
+            for project_tag in self.project_specific_generators:
+                configurations |= set(key(self.project_specific_generators[project_tag]))
+            return configurations
+
+        self.supported_project_tags = sorted(list(self.project_specific_generators.keys()))
+        self.supported_platforms = sorted(list(collect_attributes(lambda gen_cls: gen_cls.VALID_PLATFORMS)))
+        self.supported_configurations = sorted(list(collect_attributes(lambda gen_cls: gen_cls.VALID_CONFIGURATIONS)))
+
+    @util.LogEntryExit
+    def _create_parser(self):
+        valid_commands = ("generate", "generate-xcode", "check", "check-xcode", "generate-inner", "help")
+        valid_commands_prompt = "(" + " | ".join(valid_commands) + ")"
+
+        parser = argparse.ArgumentParser(add_help=False,
+                formatter_class=argparse.RawDescriptionHelpFormatter,
+                description="""\
+Generate or check .xcfilelist files. One of the following commands must be
+specified on the command-line:
+
+  generate              Generate a complete and up-to-date set of .xcfilelist
+                        files and copy them to their appropriate places in the
+                        project directories.
+  generate-xcode        Similar to generate, but to be called from within Xcode.
+  check                 Generate a complete and up-to-date set of .xcfilelist
+                        files and compare them to their counterparts in the
+                        project directories.
+  check-xcode           Similar to check, but to be called from within Xcode.
+  generate-inner        [Used by script internals] Generate an .xcfilelist file
+                        for a particular combination of project, platform, and
+                        configuration. This operation is performed in the
+                        context of an Xcode build in order to inherit the same
+                        environment as that build. Once generated, the results
+                        are returned to the calling instance of this script.
+  help                  Print this text and exit.""")
+
+        parser.add_argument("command", action=util.CheckCommandAction,
+                valid_commands=valid_commands, metavar=valid_commands_prompt,
+                help="""\
+                        The operation to perform.""")
+
+        parser.add_argument("--project", action=util.CheckValidItemAction,
+                item_type="project",
+                valid_items=self.supported_project_tags,
+                dest="project_tags", metavar="<PROJECT>", help="""\
+                        Specify which project or projects for which to generate
+                        .xcfilelist files or to check. Possible values are
+                        ({}). Can be specified more than once. Default is to
+                        iterate over all projects.""".format(
+                            ", ".join(self.supported_project_tags)))
+        parser.add_argument("--platform", action=util.CheckValidItemAction,
+                item_type="platform",
+                valid_items=self.supported_platforms,
+                aliases=self.platform_aliases,
+                dest="platforms", metavar="<PLATFORM>", help="""\
+                        Specify which platform or platforms for which to
+                        generate .xcfilelist files or to check. Possible values
+                        are ({}, plus common aliases). Can be specified more
+                        than once. Default is to iterate over all platforms,
+                        filtered to those platforms that a particular project
+                        supports (e.g., you can't specify 'iphoneos' for
+                        WebKitTestRunner).""".format(
+                            ", ".join(self.supported_platforms)))
+        parser.add_argument("--configuration", action=util.CheckValidItemAction,
+                item_type="configuration",
+                valid_items=self.supported_configurations,
+                dest="configurations", metavar="<CONFIGURATION>", help="""\
+                        Specify which configuration or configurations for which
+                        to generate .xcfilelist files or to check. Possible
+                        values are ({}). Can be specified more than once.
+                        Default is to iterate over all
+                        configurations.""".format(
+                            ", ".join(self.supported_configurations)))
+        parser.add_argument("--xcode", metavar="<WORKSPACE>", help="""\
+                        If the existing build output was created by building
+                        with Xcode, specify the path to the workspace that was
+                        used.""")
+        parser.add_argument("-d", "--debug", action="store_true", help="""\
+                        Provide verbose output.""")
+        parser.add_argument("--debug-file", help="""\
+                        [Used by script internals] Name of the file to which to
+                        write debug information. Used when this script
+                        sub-launches itself and needs to collect the debug
+                        information from the sub-launched instance. Not
+                        normally used when this script is invoked from the
+                        command-line or Xcode.""")
+        parser.add_argument("--pickle-file", help="""\
+                        [Used by script internals] Name of the file used to
+                        store results to be transported out from the Xcode
+                        execution environment out to an outer layer. This
+                        parameter is only used with the 'generate-core'
+                        command.""")
+        parser.add_argument("-q", "--quiet", action="store_true", help="""\
+                        Don't print any standard output.""")
+        parser.add_argument("-h", "--help", action="store_true", help="""\
+                        Print this text and exit.""")
+
+        setattr(parser, "application", self)
+        return parser
+
+    @util.LogEntryExit
+    def _validate_args(self, args):
+        if not self.cmd_line_args.project_tags:
+            self.cmd_line_args.project_tags = self.supported_project_tags
+        if not self.cmd_line_args.platforms:
+            self.cmd_line_args.platforms = self.supported_platforms
+        if not self.cmd_line_args.configurations:
+            self.cmd_line_args.configurations = self.supported_configurations
+
+        if util.is_running_under_xcode():
+            assert len(self.cmd_line_args.project_tags) == 1
+            assert len(self.cmd_line_args.platforms) == 1
+            assert len(self.cmd_line_args.configurations) == 1
+
+    @util.LogEntryExit
+    def _cmd_set_environment_and_generate(self):
+        generators = self._do_set_environment_and_generate()
+        generators = self._do_merge(generators)
+        return self._report_results(generators)
+
+    @util.LogEntryExit
+    def _cmd_generate_within_xcode(self):
+        generators = self._do_generate()
+        generators = self._do_merge(generators)
+        return self._report_results(generators)
+
+    @util.LogEntryExit
+    def _cmd_set_environment_and_check(self):
+        generators = self._do_set_environment_and_generate()
+        return self._report_results(generators)
+
+    @util.LogEntryExit
+    def _cmd_check_within_xcode(self):
+        generators = self._do_generate()
+        return self._report_results(generators)
+
+    @util.LogEntryExit
+    def _cmd_generate_within_xcode_and_return_results_to_caller(self):
+        generators = self._do_generate()
+        with open(self.cmd_line_args.pickle_file, "wb") as f:
+            for generator in generators:
+                generator.pickle_to_file(f)
+        return os.EX_OK
+
+    @util.LogEntryExit
+    def _cmd_help(self, status=os.EX_OK):
+        self.parser.print_help()
+        return status
+
+    @util.LogEntryExit
+    def _do_set_environment_and_generate(self):
+        def core_operation(generator, generators):
+            new_generators = generator.set_environment_and_generate()
+            generators.extend(new_generators)
+            return generators
+        return self._do_generate_common(core_operation)
+
+    @util.LogEntryExit
+    def _do_generate(self):
+        def core_operation(generator, generators):
+            generator.generate()
+            generators.append(generator)
+            return generators
+        return self._do_generate_common(core_operation)
+
+    @util.LogEntryExit
+    def _do_generate_common(self, core_operation):
+        generators = []
+
+        for triple in itertools.product(
+                self.cmd_line_args.project_tags,
+                self.cmd_line_args.platforms,
+                self.cmd_line_args.configurations):
+            generator = self.project_specific_generators[triple[0]](self, *triple)
+            if not generator.is_valid():
+                continue
+            self._log_progress("Generating .xcfilelists for {}/{}/{}".format(*triple))
+            try:
+                generators = core_operation(generator, generators)
+            except BaseException as e:
+                # TODO: Turn the traceback into a string, and then allow
+                # this field to be pickled and printed by the calling
+                # context. Right now, pickling raises an exception if it
+                # encounters a Traceback object. See BaseGenerator.pickle_to_file.
+                (generator.ex_type, generator.ex_value, generator.ex_traceback) = sys.exc_info()
+            if generator.has_error():
+                sys.exit(self._report_results([generator]))
+
+        return generators
+
+    @util.LogEntryExit
+    def _do_merge(self, generators):
+        if self._any_have_errors(generators):
+            return generators
+
+        for generator in generators:
+            if generator.has_action():
+                self._log_progress("Merging .xcfilelists for {}/{}/{}".format(*generator.triple))
+                generator.merge()
+
+        return generators
+
+    @util.LogEntryExit
+    def _report_results(self, generators):
+        generators_with_errors = [generator for generator in generators if generator.has_error()]
+        if generators_with_errors:
+            for generator in generators_with_errors:
+                generator.report_error()
+            return EX_GENERAL_ERROR
+
+        generators_with_actions = [generator for generator in generators if generator.has_action()]
+        if generators_with_actions:
+            if self.cmd_line_args.command == "generate" or self.cmd_line_args.command == "generate-xcode":
+                self._report_merge_results(generators_with_actions)
+            else:
+                self._report_remediation_steps(generators_with_actions)
+            return EX_ACTION_REQUIRED
+
+        return os.EX_OK
+
+    @util.LogEntryExit
+    def _report_merge_results(self, generators):
+        message = textwrap.wrap(
+                "\".xcfilelist\" files tell the build system what files are " +
+                "consumed and produced by the \"Run Script\" build phases in " +
+                "Xcode. At least one of these .xcfilelist files was out of date " +
+                "and has been updated. You now need to restart your build.", 90)
+
+        self._log_results("")
+        for line in message:
+            self._log_results(line)
+
+    @util.LogEntryExit
+    def _report_remediation_steps(self, generators):
+        message = textwrap.wrap("One or more \".xcfilelist\" files are out of date. Regenerate them by running the following commands:", 90)
+        message.append("")
+
+        def add_to_message(generator, message):
+            if generator.has_action():
+                message.append("    `Tools/Scripts/generate-xcfilelists generate --project {} --platform {} --configuration {}{}`\n".format(
+                        generator.project_tag, generator.platform, generator.configuration,
+                        " --xcode {}".format(self.cmd_line_args.xcode) if self.cmd_line_args.xcode else ""))
+            return message
+
+        for generator in generators:
+            message = add_to_message(generator, message)
+
+        for line in message:
+            self._log_results(line)
+
+    @util.LogEntryExit
+    def _any_have_errors(self, generators):
+        return reduce(lambda acc, generator: acc or generator.has_error(), generators, None)
+
+    @util.LogEntryExit
+    def _any_have_actions(self, generators):
+        return reduce(lambda acc, generator: acc or generator.has_action(), generators, None)
+
+    @util.LogEntryExit
+    def _log_progress(self, message):
+        if not self.cmd_line_args.quiet:
+            print("### {}".format(message))
+
+    @util.LogEntryExit
+    def _log_results(self, message):
+        if not self.cmd_line_args.quiet:
+            print("{}".format(message))
+
+    # Return the path to the script to sublaunch.
+
+    @util.LogEntryExit
+    def get_generate_xcfilelists_script_path(self):
+        return self.command_file
+
+    # Return the parent of the WebKit check-out directory.
+
+    @util.LogEntryExit
+    def _get_root_parent_dir(self):
+        return os.path.dirname(     # Remove "OpenSource"
+                os.path.dirname(        # Remove "Tools"
+                    os.path.dirname(        # Remove "Scripts"
+                        os.path.dirname(        # Remove script name
+                            self.get_generate_xcfilelists_script_path()))))
+
+    # Return the path to the WebKit check-out directory.
+
+    @util.LogEntryExit
+    def get_opensource_dir(self):
+        return os.path.join(self._get_root_parent_dir(), "OpenSource")
+
+    # Return the path to the directory containing supporting build scripts.
+
+    @util.LogEntryExit
+    def get_build_scripts_dir(self):
+        return os.path.join(self.get_opensource_dir(), "Source", "WTF", "Scripts")
+
+    # Return the path to a supporting build script.
+
+    @util.LogEntryExit
+    def get_extract_dependencies_from_makefile_script(self):
+        return os.path.join(self.get_opensource_dir(), "Tools", "Scripts", "extract-dependencies-from-makefile")
+
+    # Return $(BUILT_PRODUCTS_DIR)
+    # aka $(CONFIGURATION_BUILD_DIR)
+    # aka $(BUILD_DIR)/$(CONFIGURATION)$(EFFECTIVE_PLATFORM_NAME)
+
+    @util.LogEntryExit
+    def get_xcode_built_products_dir(self):
+        assert util.is_running_under_xcode()
+        return self._getenv("BUILT_PRODUCTS_DIR")
+
+    # Return the named environment variable.
+    @util.LogEntryExit
+    def _getenv(self, variable_name):
+        return os.environ.get(variable_name)
diff --git a/Tools/Scripts/webkitpy/generate_xcfilelists_lib/generators.py b/Tools/Scripts/webkitpy/generate_xcfilelists_lib/generators.py
new file mode 100644
index 0000000..32e5f3c
--- /dev/null
+++ b/Tools/Scripts/webkitpy/generate_xcfilelists_lib/generators.py
@@ -0,0 +1,716 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2019 Apple Inc.  All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+# OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# BaseGenerator is the base class for generating new .xcfilelist content. Most
+# of the implementation is provided in this base class. Subclasses are created
+# to provide project-specific information, such as the path to the project file
+# and valid platform and configuration information.
+#
+# Instances of this class are create for each project/platform/configuration
+# triple. For each triple, .xcfilelist content is generated and compared to the
+# file that ultimately will contain that information. Any new lines are
+# determined and remembered for later addition to that destination file.
+#
+# Instances of this class can operate in either of two contexts. First, it's
+# possible for Xcode projects to invoke this script in order to keep their
+# .xcfilelist files up-to-date. In that case, this script starts out running in
+# the context of Xcode and it can just go ahead and generate the new content.
+# Alternatively, it's possible for someone to invoke this script from the
+# command line. In that case, this script needs to sublaunch itself in order to
+# expose itself to the environment variables that Xcode establishes during
+# builds. This script thus starts out as a free-standing script, creates a
+# BaseGenerator for the .xcfilelist content it needs to create, sub-launches
+# itself, and then creates another BaseGenerator to do the actual generation.
+# When this inner instance of the script exits, it writes the results of the
+# BaseGenerators to a temporary file. When the outer instance of the script
+# resumes, it reads the information from that temporary file. That information
+# is actually just a serialized (pickled) BaseGenerator instance and is
+# restored as such. This restored BaseGenerator now replaces the original
+# BaseGenerator in the outer script that caused it to be created, since the
+# inner one is the one with all the xcfilelist information.
+
+from __future__ import print_function
+
+import os
+import pickle
+import tempfile
+import traceback
+
+import webkitpy.generate_xcfilelists_lib.util as util
+from webkitpy.xcode import xcode_hash_for_path
+from webkitpy.xcode.sdk import SDK
+from webkitpy.common.attribute_saver import AttributeSaver
+
+
+class BaseGenerator(object):
+    __slots__ = (
+        "application", "project_tag", "platform", "configuration", "triple",
+        "ex_type", "ex_value", "ex_traceback",
+        "added_lines_input_derived", "added_lines_output_derived", "added_lines_input_unified", "added_lines_output_unified",
+        "cached_build_dirs")
+
+    VALID_PLATFORMS = None
+    VALID_CONFIGURATIONS = None
+
+    @util.LogEntryExit
+    def __init__(self, application, project_tag, platform, configuration):
+        self.application = application
+        self.project_tag = project_tag
+        self.platform = platform
+        self.configuration = configuration
+        self.triple = (project_tag, platform, configuration)
+
+        self.ex_type = None
+        self.ex_value = None
+        self.ex_traceback = None
+
+        self.added_lines_input_derived = None
+        self.added_lines_output_derived = None
+        self.added_lines_input_unified = None
+        self.added_lines_output_unified = None
+
+        self.cached_build_dirs = None
+
+    def __str__(self):
+        return "project_tag = {}, platform = {}, configuration = {}, ex_type = {}, ex_value = {}, ex_traceback = {}, added_lines_input_derived = {}, added_lines_output_derived = {}, added_lines_input_unified = {}, added_lines_output_unified = {}, cached_build_dirs = {}".format(
+            self.project_tag, self.platform, self.configuration,
+            self.ex_type, self.ex_value, self.ex_traceback,
+            self.added_lines_input_derived, self.added_lines_output_derived, self.added_lines_input_unified, self.added_lines_output_unified,
+            self.cached_build_dirs)
+
+    # Generate new .xcfilist list contents and return any new lines. This
+    # generation is performed by relaunching ourselves under Xcode so that we
+    # can operate in the context of its environment variables. When we relaunch
+    # ourselves, we do so in a way that invokes this class's generate()
+    # method. Any results from generate are written to a temporary file that
+    # we set up here. When the relaunched instance completes, we reads those
+    # results from the temporary file.
+
+    @util.LogEntryExit
+    def set_environment_and_generate(self):
+        with tempfile.NamedTemporaryFile() as pickle_file, tempfile.NamedTemporaryFile() as debug_file:
+            sublaunch_args = [
+                "PATH=\"{}:${{PATH}}\"".format(self._getenv("PATH")),  # Xcode will "sanitize" PATH, such that Python is no longer on it, so get /usr/bin back in PATH.
+                "PYTHONPATH=\"{}\"".format(self._getenv("PYTHONPATH", "")),
+                self.application.get_generate_xcfilelists_script_path(),
+                "generate-inner",
+                "--project", self.project_tag,
+                "--platform", self.platform,
+                "--configuration", self.configuration,
+                "--pickle-file", pickle_file.name]
+            if self.application.cmd_line_args.debug:
+                sublaunch_args += [
+                    "--debug",
+                    "--debug-file", debug_file.name]
+            if self.application.cmd_line_args.quiet:
+                sublaunch_args.append("--quiet")
+
+            try:
+                self._sublaunch_under_xcode(sublaunch_args)
+            finally:
+                # If xcodebuild returns an error, we want to at least display the
+                # debugging information.
+                if self.application.cmd_line_args.debug:
+                    for line in debug_file:
+                        util.debug_log("{}".format(line.rstrip()))
+
+            generators = []
+            while True:
+                try:
+                    generator = pickle.load(pickle_file)
+                    generator.application = self.application
+                    generators.append(generator)
+                except EOFError as e:
+                    break
+            return generators
+
+    # Relaunch this script under Xcode. This is performed by launching Xcode,
+    # pointing it to the project that we are processing as well as a build
+    # target that will re-execute us as a custom build step.
+
+    @util.LogEntryExit
+    def _sublaunch_under_xcode(self, sublaunch_args):
+        xcode_parameters = [
+            "xcodebuild",
+            "-project", self._get_project_file_path(),
+            "-sdk", SDK.get_preferred_sdk_for_platform(self.platform).as_xcode_specification(),
+            "-configuration", self.configuration,
+            "-target", "Apply Configuration to XCFileLists",
+            "SYMROOT={}".format(self._get_sym_root()),
+            "OBJROOT={}".format(self._get_obj_root()),
+            "SHARED_PRECOMPS_DIR={}".format(self._get_shared_precomps_dir())]
+
+        # TODO: sublaunch_args will contain the path to the script to
+        # sublaunch. There might be a problem if there's a space in that path.
+        util.subprocess_run(xcode_parameters,
+            env={"WK_SUBLAUNCH_SCRIPT_PARAMETERS": " ".join(sublaunch_args)})
+
+    # Generate the .xcfilelist content. Save the results internally as sets of
+    # new lines to be added to the .xcfilelist files. These new lines can be
+    # merged into those files if the user specified a "generate" command, or
+    # can be reported in a "check" command.
+
+    @util.LogEntryExit
+    def generate(self):
+        self._generate_derived()
+        self._generate_unified()
+
+    # Merge any saved added lines to their ultimate destinations.
+
+    @util.LogEntryExit
+    def merge(self):
+        self._merge_derived()
+        self._merge_unified()
+
+    @util.LogEntryExit
+    def pickle_to_file(self, f):
+        # We don't want to pickle the application reference
+        # We can't seem to pickle ex_traceback: PicklingError: Can't pickle <type 'traceback'>: it's not found as __builtin__.traceback
+        with AttributeSaver(self, "application"), AttributeSaver(self, "ex_traceback"):
+            pickle.dump(self, f, pickle.HIGHEST_PROTOCOL)
+
+    # Return whether or not any new lines for any .xcfilelist files were
+    # discovered.
+
+    @util.LogEntryExit
+    def has_action(self):
+        return (self.added_lines_input_derived or
+                self.added_lines_output_derived or
+                self.added_lines_input_unified or
+                self.added_lines_output_unified)
+
+    # If any errors occur during the generation of .xcfilelist content, they
+    # are remembered internally for later processing. This function returns
+    # whether or not any such error occurred with this generator.
+
+    @util.LogEntryExit
+    def has_error(self):
+        return self.ex_type
+
+    # Return whether or not the combination of project, platform, and
+    # configuration is valid (which is to say, if, for example, the given
+    # project can be built for the given platform and configuration).
+
+    @util.LogEntryExit
+    def is_valid(self):
+        return (self.platform in self.__class__.VALID_PLATFORMS and
+                self.configuration in self.__class__.VALID_CONFIGURATIONS)
+
+    # If an error/exception occurred and was recorded (that is, if has_error()
+    # returns true), report that error to the console.
+
+    @util.LogEntryExit
+    def report_error(self):
+        try:
+            if self.ex_value:
+                raise self.ex_value
+        except KeyboardInterrupt:
+            print("### Canceled")
+        except util.CalledProcessError as e:
+            print("### Error {} calling subprocess: {}".format(e.args[0], e.args[1]))
+            if e.args[2]:
+                print("### stdout = {}".format(e.args[2]))
+            if e.args[3]:
+                print("### stderr = {}".format(e.args[3]))
+        except util.InvalidConfigurationError as e:
+            print("### Invalid configuration: {}".format(e))
+            return os.EX_USAGE
+        except BaseException:
+            traceback.print_exception(self.ex_type, self.ex_value, self.ex_traceback)
+            return os.EX_SOFTWARE
+
+    # Generate .xcfilelist content for the "Generate Derived Sources" build
+    # phase.
+
+    @util.LogEntryExit
+    def _generate_derived(self):
+        script = self._get_generate_derived_sources_script()
+        if not script:
+            return
+
+        with tempfile.NamedTemporaryFile() as input, tempfile.NamedTemporaryFile() as output:
+            (stdout, stderr) = util.subprocess_run(
+                    [script,
+                        "NO_SUPPLEMENTAL_FILES=1",
+                        "--no-builtin-rules",
+                        "--dry-run",
+                        "--always-make",
+                        "--debug=abvijm",
+                        "all"])
+            stdout = stdout.encode() if isinstance(stdout, str) else stdout
+            (stdout, stderr) = util.subprocess_run(
+                    [self.application.get_extract_dependencies_from_makefile_script(),
+                        "--input", input.name,
+                        "--output", output.name],
+                    input=stdout)
+
+            # TODO: Make this generator-specific (there's no need to reference
+            # WebCore, for example, when processing the JavaScriptCore
+            # project).
+
+            self._replace(input.name, "^JavaScriptCore/",               "$(PROJECT_DIR)/")
+            self._replace(input.name, "^JavaScriptCorePrivateHeaders/", "$(JAVASCRIPTCORE_PRIVATE_HEADERS_DIR)/")
+            self._replace(input.name, "^WebCore/",                      "$(PROJECT_DIR)/")
+            self._replace(input.name, "^WebKit2PrivateHeaders/",        "$(WEBKIT2_PRIVATE_HEADERS_DIR)/")
+
+            self._unexpand(input.name, "JAVASCRIPTCORE_PRIVATE_HEADERS_DIR")
+            self._unexpand(input.name, "PROJECT_DIR")
+            self._unexpand(input.name, "WEBCORE_PRIVATE_HEADERS_DIR")
+            self._unexpand(input.name, "WEBKIT2_PRIVATE_HEADERS_DIR")
+            self._unexpand(input.name, "WEBKITADDITIONS_HEADERS_FOLDER_PATH")
+            self._unexpand(input.name, "BUILT_PRODUCTS_DIR")    # Do this last, since it's a prefix of some other variables and will "intercept" them if executed earlier than them.
+
+            self._replace(output.name, "^", self._get_derived_sources_dir() + "/")
+            self._unexpand(output.name, "BUILT_PRODUCTS_DIR")
+
+            self.added_lines_input_derived = self._find_added_lines(input.name, self._get_input_derived_xcfilelist_project_path())
+            self.added_lines_output_derived = self._find_added_lines(output.name, self._get_output_derived_xcfilelist_project_path())
+
+    @util.LogEntryExit
+    def _merge_derived(self):
+        self._merge_added_lines(self.added_lines_input_derived, self._get_input_derived_xcfilelist_project_path())
+        self._merge_added_lines(self.added_lines_output_derived, self._get_output_derived_xcfilelist_project_path())
+
+    # Generate .xcfilelist content for the "Generate Unified Sources" build
+    # phase.
+
+    @util.LogEntryExit
+    def _generate_unified(self):
+        script = self._get_generate_unified_sources_script()
+        if not script:
+            return
+
+        with tempfile.NamedTemporaryFile() as output:
+
+            # We need to define BUILD_SCRIPTS_DIR so that the bash script we're
+            # invoking can find the ruby script that it invokes. If we don't
+            # define BUILD_SCRIPTS_DIR, the bash script we're invoking with try
+            # to define its own value for BUILD_SCRIPTS_DIR, but it will do so
+            # incorrectly for our purposes, leading to dire results.
+
+            env = os.environ.copy()
+            env["BUILD_SCRIPTS_DIR"] = self.application.get_build_scripts_dir()
+
+            util.subprocess_run(
+                    [script,
+                        "--generate-xcfilelists",
+                        "--output-xcfilelist-path", output.name],
+                    env=env)
+
+            self._unexpand(output.name, "BUILT_PRODUCTS_DIR")
+
+            self.added_lines_input_unified = self._find_added_lines(None, self._get_input_unified_xcfilelist_project_path())
+            self.added_lines_output_unified = self._find_added_lines(output.name, self._get_output_unified_xcfilelist_project_path())
+
+    @util.LogEntryExit
+    def _merge_unified(self):
+        self._merge_added_lines(self.added_lines_input_unified, self._get_input_unified_xcfilelist_project_path())
+        self._merge_added_lines(self.added_lines_output_unified, self._get_output_unified_xcfilelist_project_path())
+
+    # Utility for post-processing the initial .xcfilelist content. Used to
+    # replace text in the file.
+
+    @util.LogEntryExit
+    def _replace(self, file_name, to_replace, replace_with):
+        util.subprocess_run([
+            "sed", "-E", "-e",
+            "s|{}|{}|".format(to_replace, replace_with),
+            "-i", "''", file_name])
+
+    # Utility for post-processing the initial .xcfilelist content. Used to
+    # replace file path segments with the variables that represent those path
+    # segments.
+
+    @util.LogEntryExit
+    def _unexpand(self, file_name, variable_name):
+        to_replace = self._getenv(variable_name)
+        if not to_replace:
+            return
+
+        self._replace(file_name, "^{}/".format(to_replace), "$({})/".format(variable_name))
+
+    # Given a source file with new .xcfilelist content and a dest file that
+    # contains the original/previous .xcfilelist content (that is, likely the
+    # file that's checked into the repo), determine what, if any, new lines
+    # there are in source that aren't in dest.
+
+    @util.LogEntryExit
+    def _find_added_lines(self, source, dest):
+        if not source:
+            return set()
+        source_lines = set(source) if isinstance(source, list) else self._get_file_lines(source)
+        dest_lines = set(dest) if isinstance(dest, list) else self._get_file_lines(dest)
+        delta_lines = source_lines - dest_lines
+        return delta_lines
+
+    # Bottleneck routine for taking a set of new lines of .xcfilelist content
+    # and adding them to their ultimate file/destination.
+
+    @util.LogEntryExit
+    def _merge_added_lines(self, added_lines, dest):
+        if not added_lines:
+            return
+        dest_lines = self._get_file_lines(dest)
+        merged_lines = sorted(set(added_lines) | dest_lines)
+        merged_lines = [line + "\n" for line in merged_lines if line and not line.startswith("#")]
+        merged_lines[0:0] = ["# This file is generated by the generate-xcfilelists script.\n"]
+        with open(dest, "w") as f:
+            f.writelines(merged_lines)
+
+    # Utility to read a file and results the contents as a set of lines with
+    # EOLs removed.
+
+    @util.LogEntryExit
+    def _get_file_lines(self, file):
+        try:
+            with open(file, "r") as f:
+                return set([line.strip() for line in f])
+        except:
+            return set()
+
+    # Wrapper to return environment variable values.
+
+    @util.LogEntryExit
+    def _getenv(self, variable_name, default=None):
+        return os.environ.get(variable_name, default)
+
+    # Return the path to the project file (the *.xcodeproj "file).
+
+    @util.LogEntryExit
+    def _get_project_file_path(self):
+        assert False, """\
+                Override this to return full path to the project file (e.g.,
+                ".../Source/JavaScriptCore/JavaScriptCode.xcodeproj")."""
+
+    # Return the path to the directory containing the project file and its
+    # supporting files and directories (e.g., ".../Source/JavaScriptCore").
+
+    @util.LogEntryExit
+    def _get_project_dir(self):
+        return os.path.dirname(self._get_project_file_path())
+
+    # Return the project file name (e.g., "JavaScriptCore.xcodeproj").
+
+    @util.LogEntryExit
+    def _get_project_file_name(self):
+        return os.path.basename(self._get_project_file_path())
+
+    # Return the project name (e.g., "JavaScriptCore").
+
+    @util.LogEntryExit
+    def _get_project_name(self):
+        return os.path.splitext(self._get_project_file_name())[0]
+
+    # Return the path to the build output directory to use when the user has
+    # indicated that they are building from the command line. Be sure to
+    # support default command-line users, command-line users that set
+    # WEBKIT_OUTPUTDIR, default Xcode users, and people like Jeff Miller who
+    # configure a custom build output location for Xcode.
+
+    @util.LogEntryExit
+    def _get_sym_root(self):
+        return self._get_build_dirs()[0]
+
+    @util.LogEntryExit
+    def _get_obj_root(self):
+        return self._get_build_dirs()[1]
+
+    @util.LogEntryExit
+    def _get_shared_precomps_dir(self):
+        return os.path.join(self._get_build_dirs()[1], "PrecompiledHeaders")
+
+    # From Xcode;
+    #
+    #   export SYMROOT            =/Users/keith/Library/Developer/Xcode/DerivedData/Safari-bmjhivzkbpxamlajyexvkivfjbmb/Build/Products
+    #   export OBJROOT            =/Users/keith/Library/Developer/Xcode/DerivedData/Safari-bmjhivzkbpxamlajyexvkivfjbmb/Build/Intermediates.noindex
+    #   export SHARED_PRECOMPS_DIR=/Users/keith/Library/Developer/Xcode/DerivedData/Safari-bmjhivzkbpxamlajyexvkivfjbmb/Build/Intermediates.noindex/PrecompiledHeaders
+    #
+    # From command-line:
+    #
+    #   export SYMROOT            =/Volumes/Data/dev/webkit/OpenSource/WebKitBuild
+    #   export OBJROOT            =/Volumes/Data/dev/webkit/OpenSource/WebKitBuild
+    #   export SHARED_PRECOMPS_DIR=/Volumes/Data/dev/webkit/OpenSource/WebKitBuild/PrecompiledHeaders
+
+    @util.LogEntryExit
+    def _get_build_dirs(self):
+        def define_xcode_build_dirs(self):
+            # Delete any spurious ~/Library/Preferences/xcodebuild.plist, as this
+            # file will interfere with any preferences set in the IDE. This
+            # .plist file shouldn't really ever exist, so nuking it doesn't
+            # cause any problems.
+
+            xcodebuild_plist = os.path.join(os.path.expanduser("~"), "Library", "Preferences", "xcodebuild.plist")
+            try:
+                os.unlink(xcodebuild_plist)
+            except:
+                pass
+
+            def read_xcode_user_default(key):
+                try:
+                    (stdout, stderr) = util.subprocess_run(["defaults", "read", "com.apple.dt.Xcode", key])
+                    return stdout.strip()
+                except util.CalledProcessError:
+                    return None
+
+            # The following is based on the logic in determineBaseProductDir()
+            # in webkitdirs.pm and https://pewpewthespells.com/blog/xcode_build_locations.html.
+
+            # Get the base directory for the build output. This will be some
+            # default location (e.g., ~/Library/Developer/Xcode/DerivedData),
+            # an absolute path, or a project-relative path.
+
+            ide_custom_derived_data_location = read_xcode_user_default("IDECustomDerivedDataLocation")
+
+            # Path not specified; use the default.
+
+            if not ide_custom_derived_data_location:
+                base_dir = os.path.join(os.path.expanduser("~"), "Library", "Developer", "Xcode", "DerivedData")
+
+            # An absolute path is specified; use it.
+
+            elif os.path.isabs(ide_custom_derived_data_location):
+                base_dir = ide_custom_derived_data_location
+
+            # A relative path is specified; append it to the project path.
+
+            else:
+                base_dir = os.path.join(self._get_project_dir(), ide_custom_derived_data_location)
+
+            # Get the specification for how the build output should be stored
+            # withing that base directory. This will be some unique directory
+            # based on the hash of the project file path (e.g.,
+            # "Safari-sdlfkhasalksdjfhsdfhlksf"), some shared directory (e.g.,
+            # "Build"), or even something that might be an absolute path.
+
+            ide_build_location_style = read_xcode_user_default("IDEBuildLocationStyle")
+
+            # Create a unique directory within the base directory based on
+            # project name and hash of its full path.
+            #
+            #    IDEBuildLocationStyle      = Unique;       # This is the default if not specified.
+
+            if ide_build_location_style == "Unique" or not ide_build_location_style:
+                workspace = os.path.abspath(self.application.cmd_line_args.xcode)
+                build_dir = os.path.join(
+                        base_dir,
+                        os.path.splitext(os.path.basename(workspace))[0] + "-" + xcode_hash_for_path(workspace),
+                        "Build")
+                products_dir = os.path.join(build_dir, "Products")
+                intermediates_dir = os.path.join(build_dir, "Intermediates.noindex")
+
+            # Use a shared subdirectory; use the specified directory name.
+            #
+            #    IDEBuildLocationStyle      = Shared;
+            #    IDESharedBuildFolderName       = Build;    # Relative to DerivedDataLocation
+
+            elif ide_build_location_style == "Shared":
+                build_dir = os.path.join(base_dir, read_xcode_user_default("IDESharedBuildFolderName"))
+                products_dir = os.path.join(build_dir, "Products")
+                intermediates_dir = os.path.join(build_dir, "Intermediates.noindex")
+
+            # Use the saved products and intermediates paths and either use
+            # them as relative to the DerivedData directory or the project
+            # folder, or just use them as absolute addresses.
+            #
+            #    IDEBuildLocationStyle      = Custom;
+
+            elif ide_build_location_style == "Custom":
+                ide_build_location_type = read_xcode_user_default("IDECustomBuildLocationType")
+
+                products_dir = read_xcode_user_default("IDECustomBuildProductsPath")
+                intermediates_dir = read_xcode_user_default("IDECustomBuildIntermediatesPath")
+
+                #    IDECustomBuildLocationType     = RelativeToDerivedData;
+                #    IDECustomBuildIntermediatesPath    = "Build/Intermediates.noindex";
+                #    IDECustomBuildProductsPath         = "Build/Products";
+                #    IDECustomIndexStorePath            = "Index/DataStore";
+
+                if ide_build_location_type == "RelativeToDerivedData":
+                    products_dir = os.path.join(base_dir, products_dir)
+                    intermediates_dir = os.path.join(base_dir, intermediates_dir)
+
+                #    IDECustomBuildLocationType     = RelativeToWorkspace;
+                #    IDECustomBuildIntermediatesPath    = "Build/Intermediates.noindex";
+                #    IDECustomBuildProductsPath         = "Build/Products";
+                #    IDECustomIndexStorePath            = "Index/DataStore";
+
+                elif ide_build_location_type == "RelativeToWorkspace":
+                    base_dir = self._get_project_dir(),
+                    products_dir = os.path.join(base_dir, products_dir)
+                    intermediates_dir = os.path.join(base_dir, intermediates_dir)
+
+                #    IDECustomBuildLocationType     = Absolute;
+                #    IDECustomBuildIntermediatesPath    = "/Users/joedeveloper/Desktop/Build/Intermediates.noindex";
+                #    IDECustomBuildProductsPath         = "/Users/joedeveloper/Desktop/Build/Products";
+                #    IDECustomIndexStorePath            = "/Users/joedeveloper/Desktop/Index/DataStore";
+                #    IDECustomDerivedDataLocation       = "/Users/joedeveloper/Library/Developer/Xcode/DerivedData";
+
+                elif ide_build_location_type == "Absolute":
+                    pass
+
+                else:
+                    assert False, "Unknown/unsupported location type"
+            else:
+                assert False, "Unknown/unsupported style"
+
+            return (products_dir, intermediates_dir)
+
+        def define_command_line_build_dirs(self):
+            products_dir = self._getenv("WEBKIT_OUTPUTDIR")
+            if not products_dir:
+                products_dir = os.path.join(self.application.get_opensource_dir(), "WebKitBuild")
+            return (products_dir, products_dir)
+
+        if not self.cached_build_dirs and self.application.cmd_line_args.xcode:
+            self.cached_build_dirs = define_xcode_build_dirs(self)
+        if not self.cached_build_dirs:
+            self.cached_build_dirs = define_command_line_build_dirs(self)
+        return self.cached_build_dirs
+
+    # Return the location of the DerivedSources directory. Conventionally, we
+    # use $BUILT_PRODUCTS/DerivedSources/$PROJECT_NAME, but we may some day use
+    # $DERIVED_FILE_DIR aka $DERIVED_FILES_DIR aka $DERIVED_SOURCES_DIR, when
+    # the projects have been updated to use them.
+
+    @util.LogEntryExit
+    def _get_derived_sources_dir(self):
+        return os.path.join(self.application.get_xcode_built_products_dir(), "DerivedSources", self._get_project_name())
+
+    # Return the location for the xcfilelists.
+
+    @util.LogEntryExit
+    def _get_xcfilelist_dir(self):
+        return self._get_project_dir()
+
+    # Return the paths to the actual xcfilelists.
+
+    @util.LogEntryExit
+    def _get_input_derived_xcfilelist_project_path(self):
+        return os.path.join(self._get_xcfilelist_dir(), "DerivedSources-input.xcfilelist")
+
+    @util.LogEntryExit
+    def _get_output_derived_xcfilelist_project_path(self):
+        return os.path.join(self._get_xcfilelist_dir(), "DerivedSources-output.xcfilelist")
+
+    @util.LogEntryExit
+    def _get_input_unified_xcfilelist_project_path(self):
+        return os.path.join(self._get_xcfilelist_dir(), "UnifiedSources-input.xcfilelist")
+
+    @util.LogEntryExit
+    def _get_output_unified_xcfilelist_project_path(self):
+        return os.path.join(self._get_xcfilelist_dir(), "UnifiedSources-output.xcfilelist")
+
+    # Return the paths to the scripts that generate the derived sources.
+
+    @util.LogEntryExit
+    def _get_generate_derived_sources_script(self):
+        return None
+
+    @util.LogEntryExit
+    def _get_generate_unified_sources_script(self):
+        return None
+
+
+class JavaScriptCoreGenerator(BaseGenerator):
+    VALID_PLATFORMS = ("macosx", "iosmac", "iphoneos", "watchos")
+    VALID_CONFIGURATIONS = ("Debug", "Release", "Production", "Profiling")
+
+    @util.LogEntryExit
+    def _get_project_file_path(self):
+        return os.path.join(self.application.get_opensource_dir(), "Source", "JavaScriptCore", "JavaScriptCore.xcodeproj")
+
+    @util.LogEntryExit
+    def _get_generate_derived_sources_script(self):
+        return os.path.join(self._get_project_dir(), "Scripts", "generate-derived-sources.sh")
+
+    @util.LogEntryExit
+    def _get_generate_unified_sources_script(self):
+        return os.path.join(self._get_project_dir(), "Scripts", "generate-unified-sources.sh")
+
+
+class WebCoreGenerator(BaseGenerator):
+    VALID_PLATFORMS = ("macosx", "iosmac", "iphoneos", "watchos")
+    VALID_CONFIGURATIONS = ("Debug", "Release", "Production")
+
+    @util.LogEntryExit
+    def _get_project_file_path(self):
+        return os.path.join(self.application.get_opensource_dir(), "Source", "WebCore", "WebCore.xcodeproj")
+
+    @util.LogEntryExit
+    def _get_generate_derived_sources_script(self):
+        return os.path.join(self._get_project_dir(), "Scripts", "generate-derived-sources.sh")
+
+    @util.LogEntryExit
+    def _get_generate_unified_sources_script(self):
+        return os.path.join(self._get_project_dir(), "Scripts", "generate-unified-sources.sh")
+
+
+class WebKitGenerator(BaseGenerator):
+    VALID_PLATFORMS = ("macosx", "iosmac", "iphoneos", "watchos")
+    VALID_CONFIGURATIONS = ("Debug", "Release", "Production")
+
+    @util.LogEntryExit
+    def _get_project_file_path(self):
+        return os.path.join(self.application.get_opensource_dir(), "Source", "WebKit", "WebKit.xcodeproj")
+
+    @util.LogEntryExit
+    def _get_derived_sources_dir(self):
+        return os.path.join(self.application.get_xcode_built_products_dir(), "DerivedSources", "WebKit2")
+
+    @util.LogEntryExit
+    def _get_generate_derived_sources_script(self):
+        return os.path.join(self._get_project_dir(), "Scripts", "generate-derived-sources.sh")
+
+    @util.LogEntryExit
+    def _get_generate_unified_sources_script(self):
+        return os.path.join(self._get_project_dir(), "Scripts", "generate-unified-sources.sh")
+
+
+class DumpRenderTreeGenerator(BaseGenerator):
+    VALID_PLATFORMS = ("macosx", )
+    VALID_CONFIGURATIONS = ("Debug", "Release", "Production")
+
+    @util.LogEntryExit
+    def _get_project_file_path(self):
+        return os.path.join(self.application.get_opensource_dir(), "Tools", "DumpRenderTree", "DumpRenderTree.xcodeproj")
+
+    @util.LogEntryExit
+    def _get_generate_derived_sources_script(self):
+        return os.path.join(self._get_project_dir(), "Scripts", "generate-derived-sources.sh")
+
+
+class WebKitTestRunnerGenerator(BaseGenerator):
+    VALID_PLATFORMS = ("macosx", )
+    VALID_CONFIGURATIONS = ("Debug", "Release", "Production")
+
+    @util.LogEntryExit
+    def _get_project_file_path(self):
+        return os.path.join(self.application.get_opensource_dir(), "Tools", "WebKitTestRunner", "WebKitTestRunner.xcodeproj")
+
+    @util.LogEntryExit
+    def _get_generate_derived_sources_script(self):
+        return os.path.join(self._get_project_dir(), "Scripts", "generate-derived-sources.sh")
diff --git a/Tools/Scripts/webkitpy/generate_xcfilelists_lib/util.py b/Tools/Scripts/webkitpy/generate_xcfilelists_lib/util.py
new file mode 100644
index 0000000..33ffe1b
--- /dev/null
+++ b/Tools/Scripts/webkitpy/generate_xcfilelists_lib/util.py
@@ -0,0 +1,292 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2019 Apple Inc.  All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+# OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+from __future__ import print_function
+
+import argparse
+import os
+import subprocess
+import sys
+import traceback
+
+# Gather information about our debugging environment right now. Do this before
+# executing any "main" code so that our debugging preferences are in place by
+# the time we get there and we can debug from main() on down as opposed to
+# parse_args() on down.
+
+SHOW_DEBUG_LOGGING = "-d" in sys.argv or "--debug" in sys.argv
+
+if SHOW_DEBUG_LOGGING:
+
+    DEBUG_LOGGING_FILE = None
+    for index, arg in enumerate(sys.argv):
+        if arg == "--debug-file":
+            if index + 1 < len(sys.argv):
+                DEBUG_LOGGING_FILE = sys.argv[index + 1]
+
+    # Bottleneck function for printing debugging lines to either the console or
+    # the screen, as appropriate.
+
+    if DEBUG_LOGGING_FILE:
+
+        def debug_log(msg):
+            with open(DEBUG_LOGGING_FILE, "a") as f:
+                print(msg, file=f)
+    else:
+
+        def debug_log(msg):
+            print(msg)
+
+    # Context Manager class for logging information about function entry/exit.
+    # On entry, the function name is logged along with its parameters. On exit,
+    # the function name is logged with its result. If an exception occurs, the
+    # function name is logged with the exception. In all cases, the logging is
+    # indented according to the level of the function in the backtrace.
+    #
+    # Versions of these classes exist for instance methods, class methods, and
+    # global functions so that instance and class information can be extracted
+    # and displayed.
+
+    class LogEntryHelper(object):
+        __slots__ = ["indent", "class_name", "function_name", "type"]
+
+        def __init__(self, func, type):
+            tb = traceback.extract_stack()
+            self.indent = " " * 2 * (len(tb) - 3)
+            self.class_name = None
+            self.function_name = func.__name__
+            self.type = type
+
+        def log_entry(self, args, kwargs):
+            if self.type == "instance":
+                self.class_name = args[0].__class__.__name__ + "."
+                args = args[1:]
+            elif self.type == "class":
+                self.class_name = args[0].__name__ + "."
+                args = args[1:]
+            else:
+                self.class_name = ""
+
+            self._print("args={}, kwargs={}".format(args, kwargs))
+
+        def log_result(self, result):
+            if hasattr(result, '__iter__') and not isinstance(result, str):
+                for line in result:
+                    self._print("result={}".format(line))
+            else:
+                self._print("result={}".format(result))
+
+        def log_exception(self, exc):
+            self._print("exception={}".format(exc))
+
+        def _print(self, msg):
+            debug_log("{}{}{}: {}".format(self.indent, self.class_name, self.function_name, msg))
+
+    def LogEntryExit(func):
+        def _show_debug_logging(*args, **kwargs):
+            helper = LogEntryHelper(func, "instance")
+            helper.log_entry(args, kwargs)
+            try:
+                result = func(*args, **kwargs)
+                helper.log_result(result)
+                return result
+            except BaseException as e:
+                helper.log_exception(e)
+                raise
+        return _show_debug_logging
+
+    def LogEntryExitClass(func):
+        def _show_debug_logging(*args, **kwargs):
+            helper = LogEntryHelper(func, "class")
+            helper.log_entry(args, kwargs)
+            try:
+                result = func(*args, **kwargs)
+                helper.log_result(result)
+                return result
+            except BaseException as e:
+                helper.log_exception(e)
+                raise
+        return _show_debug_logging
+
+    def LogEntryExitGlobal(func):
+        def _show_debug_logging(*args, **kwargs):
+            helper = LogEntryHelper(func, None)
+            helper.log_entry(args, kwargs)
+            try:
+                result = func(*args, **kwargs)
+                helper.log_result(result)
+                return result
+            except BaseException as e:
+                helper.log_exception(e)
+                raise
+        return _show_debug_logging
+
+else:
+
+    def debug_log(msg):
+        pass
+
+    def LogEntryExit(func):
+        return func
+
+    def LogEntryExitClass(func):
+        return func
+
+    def LogEntryExitGlobal(func):
+        return func
+
+
+# Utility function for operating similar to subprocess.run() in Python 3. One
+# difference is that the result is a 2-tuple with stdout and stderr, rather
+# than a 3-tuple that includes returncode. For our purposes, if returncode is
+# non-zero, we raise an exception.
+
+@LogEntryExitGlobal
+def subprocess_run(args, **kwargs):
+    kwargs["stdout"] = subprocess.PIPE
+    kwargs["stderr"] = subprocess.PIPE
+    input = None
+    if "input" in kwargs:
+        input = kwargs["input"]
+        del kwargs["input"]
+        kwargs["stdin"] = subprocess.PIPE
+    process = subprocess.Popen(args, **kwargs)
+    (stdout, stderr) = process.communicate(input=input)
+    stdout = stdout.decode() if isinstance(stdout, bytes) else stdout
+    stderr = stderr.decode() if isinstance(stderr, bytes) else stderr
+    if process.returncode:
+        raise CalledProcessError(process.returncode, args[0], stdout, stderr)
+    return (stdout, stderr)
+
+
+# Utility function to allow us to verify that we're running under Xcode or not.
+# For example, if we are not, then we need to make sure that we don't try to
+# access Xcode-specific environment variables.
+
+@LogEntryExitGlobal
+def is_running_under_xcode():
+    return os.environ.get("XCODE_INSTALL_PATH")
+
+
+# An argparse.Action subclass that validates the user-provided value against a
+# list of valid values. Aliasing is supported; that is, the user can provide a
+# value that can get mapped to a corresponding canonical value, and that
+# resulting value is compared to the list of valid values.
+#
+# On error, calls parser.error().
+
+class CheckValidItemAction(argparse.Action):
+    @LogEntryExit
+    def __init__(self, *args, **kwargs):
+        self.item_type = kwargs.get("item_type", None)
+        self.valid_items = kwargs.get("valid_items", None)
+        self.aliases = kwargs.get("aliases", None)
+
+        self.lowered_valid_items = [item.lower() for item in self.valid_items]
+
+        kwargs.pop("item_type", None)
+        kwargs.pop("valid_items", None)
+        kwargs.pop("aliases", None)
+
+        super(CheckValidItemAction, self).__init__(*args, **kwargs)
+
+    @LogEntryExit
+    def __call__(self, parser, namespace, values, option_string=None):
+        try:
+            validated = self.validate_item(values)
+        except:
+            parser.error("The {} \"{}\" is not supported.".format(self.item_type, values))
+        items = getattr(namespace, self.dest, None)
+        items = items[:] if items else []
+        items.append(validated)
+        setattr(namespace, self.dest, items)
+
+    @LogEntryExit
+    def validate_item(self, item):
+        item = item.lower()
+        try:
+            validated_index = self.lowered_valid_items.index(item)
+        except:
+            if not self.aliases:
+                raise
+            item = self.aliases.get(item, None)
+            validated_index = self.lowered_valid_items.index(item)
+        return self.valid_items[validated_index]
+
+
+# An argparse.Action subclass that validates the user-provided script command
+# (generate, check, etc.)
+#
+# On error, calls parser.error().
+
+class CheckCommandAction(argparse.Action):
+    @LogEntryExit
+    def __init__(self, *args, **kwargs):
+        self.valid_commands = kwargs.get("valid_commands", None)
+        kwargs.pop("valid_commands", None)
+        super(CheckCommandAction, self).__init__(*args, **kwargs)
+
+    @LogEntryExit
+    def __call__(self, parser, namespace, value, option_string=None):
+        if not value in self.valid_commands:
+            parser.error('"{}" is not a valid command'.format(value))
+        setattr(namespace, self.dest, value)
+
+
+# Some Exceptions
+
+class InvalidCommandError(Exception):
+    pass
+
+
+class InvalidArgumentError(Exception):
+    pass
+
+
+class InvalidConfigurationError(Exception):
+    pass
+
+
+# subprocess.CalledProcessError has problems with being pickled, which is
+# something that we do to it. In particular, when unpickled, it throws an
+# exception, and so CalledProcessError get's turned into an exception saying
+# "__init__() takes at least 3 arguments (1 given)". Address this by creating
+# our own CalledProcessError that's a little more generic.
+
+class CalledProcessError(Exception):
+    def __str__(self):
+        returncode = self.args[0] if len(self.args) > 0 else None
+        command = self.args[1] if len(self.args) > 1 else None
+        stdout = self.args[2] if len(self.args) > 2 else None
+        stderr = self.args[3] if len(self.args) > 3 else None
+
+        if stderr:
+            return "Command '{}' returned non-zero exit status {}: {}".format(command, returncode, stderr)
+        elif stdout:
+            return "Command '{}' returned non-zero exit status {}: {}".format(command, returncode, stdout)
+        else:
+            return "Command '{}' returned non-zero exit status {}".format(command, returncode)
diff --git a/Tools/Scripts/webkitpy/xcode/__init__.py b/Tools/Scripts/webkitpy/xcode/__init__.py
index ef65bee..7a218c8 100644
--- a/Tools/Scripts/webkitpy/xcode/__init__.py
+++ b/Tools/Scripts/webkitpy/xcode/__init__.py
@@ -1 +1,26 @@
 # Required for Python to search this directory for module files
+
+import hashlib
+import struct
+
+
+# The default location for Xcode's "DerivedData" (build output and intermediate
+# files) is a unique directory in ~/Library/Developer/Xcode/DerivedData with a
+# name incorporating a hash based on the full path of the project or workspace
+# being built. The following function takes that path and returns the
+# corresponding hash.
+#
+# The algorithm is adapted from the following article:
+#
+#   <https://pewpewthespells.com/blog/xcode_deriveddata_hashes.pdf>
+
+def xcode_hash_for_path(path):
+    def convert_to_string(n):
+        s = ''
+        for _ in range(0, 14):
+            (n, r) = divmod(n, 26)
+            s = chr(r + 97) + s
+        return s
+
+    (part1, part2) = struct.unpack(">QQ", hashlib.md5(path.encode()).digest())
+    return convert_to_string(part1) + convert_to_string(part2)
diff --git a/Tools/Scripts/webkitpy/xcode/sdk.py b/Tools/Scripts/webkitpy/xcode/sdk.py
new file mode 100644
index 0000000..3368128
--- /dev/null
+++ b/Tools/Scripts/webkitpy/xcode/sdk.py
@@ -0,0 +1,123 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2019 Apple Inc.  All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+# OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+# Class for representing SDK information, in the form of Platform, Version, and
+# whether or not it's an Internal SDK. This class also contains a factory
+# method for producing an SDK instance from a "specification" string such as
+# "macOS15.3Internal", like you would get from 'xcodebuild -showsdks".
+
+
+import re
+
+from webkitpy.common.system.executive import Executive
+
+
+test_output = None
+
+
+class SDK(object):
+    __slots__ = ["xcode_specification", "platform", "version", "internal"]
+
+    def __init__(self, xcode_specification, platform, version, internal):
+        super(SDK, self).__init__()
+        self.xcode_specification = xcode_specification
+        self.platform = platform
+        self.version = version
+        self.internal = internal
+
+    def __repr__(self):
+        return "SDK({}, {}, {}, {})".format(
+                self.xcode_specification,
+                self.platform,
+                self.version,
+                self.internal)
+
+    def as_xcode_specification(self):
+        return "{}.internal".format(self.platform) if self.internal else self.platform
+
+    @classmethod
+    def get_preferred_sdk_for_platform(cls, platform, executive=None):
+
+        preferred_sdk = cls._parse_sdk(platform)
+
+        executive = executive or Executive()
+        stdout = executive.run_command(["xcodebuild", "-showsdks"])
+
+        for line in stdout.splitlines():
+            m = re.match(r".*-sdk (.*)", line)
+            if m:
+                this_sdk = cls._parse_sdk(m.group(1))
+
+                if preferred_sdk.platform != this_sdk.platform:
+                    continue
+
+                # Both have version information, so compare versions. If the
+                # versions are equal, prefer the Internal sdk. Otherwise, keep
+                # the one with the higher version.
+
+                if preferred_sdk.version and this_sdk.version:
+                    if float(preferred_sdk.version) == float(this_sdk.version):
+                        if this_sdk.internal:
+                            preferred_sdk = this_sdk
+                    elif float(preferred_sdk.version) < float(this_sdk.version):
+                        preferred_sdk = this_sdk
+
+                # The preferred sdk does not have a version but the prospective
+                # one does, so keep the prospective one.
+
+                elif not preferred_sdk.version and this_sdk.version:
+                    preferred_sdk = this_sdk
+
+                # The preferred sdk has a version but the prospective one does
+                # not, so keep the preferred one.
+
+                elif preferred_sdk.version and not this_sdk.version:
+                    pass
+
+                # Neither has version information; prefer the current one if
+                # it's internal.
+
+                elif not preferred_sdk.version and not this_sdk.version:
+                    if this_sdk.internal:
+                        preferred_sdk = this_sdk
+
+        return preferred_sdk
+
+    @classmethod
+    def _parse_sdk(cls, xcode_specification):
+        # letters-and-dots, followed by optional numbers-and-dots, followed by
+        # an optional "internal"
+        m = re.match(r"([a-zA-Z.]+[a-zA-Z])([0-9.]+[0-9])?\.?(internal)?", xcode_specification)
+        if not m:
+            return SDK(xcode_specification, None, None, None)
+
+        platform = m.group(1)
+        version = m.group(2)
+        internal = m.group(3)
+
+        return SDK(xcode_specification, platform, version, internal)
diff --git a/Tools/Scripts/webkitpy/xcode/sdk_unittest.py b/Tools/Scripts/webkitpy/xcode/sdk_unittest.py
new file mode 100644
index 0000000..0cdf34c
--- /dev/null
+++ b/Tools/Scripts/webkitpy/xcode/sdk_unittest.py
@@ -0,0 +1,119 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2019 Apple Inc.  All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+# PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+# OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+import unittest
+
+import webkitpy.xcode.sdk as sdk
+from webkitpy.common.system.executive_mock import MockExecutive2
+
+
+class SDKTest(unittest.TestCase):
+
+    TEST_XCODEBUILD_SHOWSDKS_OUTPUT = """\
+        iOS SDKs:
+        \tiOS 12.0                      \t-sdk iphoneos12.0
+        \tiOS 12.0 Internal             \t-sdk iphoneos12.0.internal
+
+        iOS Simulator SDKs:
+        \tSimulator - iOS 12.0          \t-sdk iphonesimulator12.0
+
+        macOS SDKs:
+        \tmacOS 10.13                   \t-sdk macosx10.13
+        \tmacOS 10.13 Internal          \t-sdk macosx10.13internal
+        \tmacOS 10.14                   \t-sdk macosx10.14
+        \tmacOS 10.14 Internal          \t-sdk macosx10.14internal
+
+        tvOS SDKs:
+        \ttvOS 12.0                     \t-sdk appletvos12.0
+        \ttvOS 12.0 Internal            \t-sdk appletvos12.0.internal
+
+        tvOS Simulator SDKs:
+        \tSimulator - tvOS 12.0         \t-sdk appletvsimulator12.0
+
+        watchOS SDKs:
+        \twatchOS 4.0                   \t-sdk watchos4.0
+        \twatchOS 4.0 Internal          \t-sdk watchos4.0.internal
+
+        watchOS Simulator SDKs:
+        \tSimulator - watchOS 4.0       \t-sdk watchsimulator4.0
+        """
+
+    @classmethod
+    def setUpClass(cls):
+        cls.executive = MockExecutive2(output=cls.TEST_XCODEBUILD_SHOWSDKS_OUTPUT)
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.executive = None
+
+    def test_iphoneos(self):
+        preferred_sdk = sdk.SDK.get_preferred_sdk_for_platform("iphoneos", self.executive)
+        self.assertEquals("iphoneos", preferred_sdk.platform)
+        self.assertEquals("12.0", preferred_sdk.version)
+        self.assertTrue(preferred_sdk.internal)
+
+    def test_iphonesim(self):
+        preferred_sdk = sdk.SDK.get_preferred_sdk_for_platform("iphonesimulator", self.executive)
+        self.assertEquals("iphonesimulator", preferred_sdk.platform)
+        self.assertEquals("12.0", preferred_sdk.version)
+        self.assertFalse(preferred_sdk.internal)
+
+    def test_macos(self):
+        preferred_sdk = sdk.SDK.get_preferred_sdk_for_platform("macosx", self.executive)
+        self.assertEquals("macosx", preferred_sdk.platform)
+        self.assertEquals("10.14", preferred_sdk.version)
+        self.assertTrue(preferred_sdk.internal)
+
+    def test_appletvos(self):
+        preferred_sdk = sdk.SDK.get_preferred_sdk_for_platform("appletvos", self.executive)
+        self.assertEquals("appletvos", preferred_sdk.platform)
+        self.assertEquals("12.0", preferred_sdk.version)
+        self.assertTrue(preferred_sdk.internal)
+
+    def test_appletvsim(self):
+        preferred_sdk = sdk.SDK.get_preferred_sdk_for_platform("appletvsimulator", self.executive)
+        self.assertEquals("appletvsimulator", preferred_sdk.platform)
+        self.assertEquals("12.0", preferred_sdk.version)
+        self.assertFalse(preferred_sdk.internal)
+
+    def test_watchos(self):
+        preferred_sdk = sdk.SDK.get_preferred_sdk_for_platform("watchos", self.executive)
+        self.assertEquals("watchos", preferred_sdk.platform)
+        self.assertEquals("4.0", preferred_sdk.version)
+        self.assertTrue(preferred_sdk.internal)
+
+    def test_watchsimulator(self):
+        preferred_sdk = sdk.SDK.get_preferred_sdk_for_platform("watchsimulator", self.executive)
+        self.assertEquals("watchsimulator", preferred_sdk.platform)
+        self.assertEquals("4.0", preferred_sdk.version)
+        self.assertFalse(preferred_sdk.internal)
+
+    def test_prodos(self):
+        preferred_sdk = sdk.SDK.get_preferred_sdk_for_platform("prodos", self.executive)
+        self.assertEquals("prodos", preferred_sdk.platform)
+        self.assertEquals(None, preferred_sdk.version)
+        self.assertEquals(None, preferred_sdk.internal)
diff --git a/Tools/WebKitTestRunner/Scripts/check-xcfilelists.sh b/Tools/WebKitTestRunner/Scripts/check-xcfilelists.sh
index 9cf827c..fe3ec48 100755
--- a/Tools/WebKitTestRunner/Scripts/check-xcfilelists.sh
+++ b/Tools/WebKitTestRunner/Scripts/check-xcfilelists.sh
@@ -8,6 +8,7 @@
 [ "${USE_INTERNAL_SDK}" == "YES" ] || { echo "### Not running because USE_INTERNAL_SDK is not YES"; exit 0; }
 
 SCRIPT="${BUILD_SCRIPTS_DIR}/generate-xcfilelists"
+[ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../../${WK_ADDITIONAL_SCRIPTS_DIR}/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || SCRIPT="${PROJECT_DIR}/../../Tools/Scripts/generate-xcfilelists"
 [ -f "${SCRIPT}" ] || { echo "### Cannot find generate-xcfilelists script"; exit 1; }