build/toolchain/apple/toolchain.gni - cobalt - Git at Google

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.

 # TODO(brettw) Use "gcc_toolchain.gni" like the Linux toolchains. This requires
 # some enhancements since the commands on Mac are slightly different than on
 # Linux.

 import("//build/config/apple/symbols.gni")
 import("//build/config/clang/clang.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/coverage/coverage.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")

 assert((target_os == "ios" && host_os == "mac") || host_os != "win")

 declare_args() {
   # This makes the linker set timestamps in Mach-O files to 0. This isn't
   # enabled by default because this breaks Xcode's lldb. This has been fixed in
   # https://reviews.llvm.org/rL368199 but that has not yet made it into a public
   # lldb release.
   mac_deterministic_build = false

   # This controls whether whole module optimization is enabled when building
   # Swift modules. If enabled, the compiler will compile the module as one
   # unit, generating just one single object file. Otherwise, it will generate
   # one object file per .swift file. If unspecified, will default to "true"
   # for official builds, and "false" for all other builds.
   swift_whole_module_optimization = -1
 }

 if (swift_whole_module_optimization == -1) {
   swift_whole_module_optimization = is_official_build
 }

 # When implementing tools using Python scripts, a TOOL_VERSION=N env
 # variable is placed in front of the command. The N should be incremented
 # whenever the script is changed, so that the build system rebuilds all
 # edges that utilize the script. Ideally this should be changed to use
 # proper input-dirty checking, but that could be expensive. Instead, use a
 # script to get the tool scripts' modification time to use as the version.
 # This won't cause a re-generation of GN files when the tool script changes
 # but it will cause edges to be marked as dirty if the ninja files are
 # regenerated. See https://crbug.com/619083 for details. A proper fix
 # would be to have inputs to tools (https://crbug.com/621119).
 tool_versions =
     exec_script("get_tool_mtime.py",
                 rebase_path([
                               "//build/toolchain/apple/filter_libtool.py",
                               "//build/toolchain/apple/linker_driver.py",
                               "//build/toolchain/ios/compile_xcassets.py",
                               "//build/toolchain/ios/swiftc.py",
                             ],
                             root_build_dir),
                 "trim scope")

 # Shared toolchain definition. Invocations should set current_os to set the
 # build args in this definition.
 template("apple_toolchain") {
   toolchain(target_name) {
     # When invoking this toolchain not as the default one, these args will be
     # passed to the build. They are ignored when this is the default toolchain.
     assert(defined(invoker.toolchain_args),
            "Toolchains must declare toolchain_args")
     toolchain_args = {
       # Populate toolchain args from the invoker.
       forward_variables_from(invoker.toolchain_args, "*")

       # The host toolchain value computed by the default toolchain's setup
       # needs to be passed through unchanged to all secondary toolchains to
       # ensure that it's always the same, regardless of the values that may be
       # set on those toolchains.
       host_toolchain = host_toolchain
     }

     # When the invoker has explicitly overridden use_goma or cc_wrapper in the
     # toolchain args, use those values, otherwise default to the global one.
     # This works because the only reasonable override that toolchains might
     # supply for these values are to force-disable them.
     if (defined(toolchain_args.use_goma)) {
       toolchain_uses_goma = toolchain_args.use_goma
     } else {
       toolchain_uses_goma = use_goma
     }
     if (defined(toolchain_args.cc_wrapper)) {
       toolchain_cc_wrapper = toolchain_args.cc_wrapper
     } else {
       toolchain_cc_wrapper = cc_wrapper
     }
     if (defined(toolchain_args.use_xcode_clang)) {
       toolchain_uses_xcode_clang = toolchain_args.use_xcode_clang
     } else {
       toolchain_uses_xcode_clang = use_xcode_clang
     }

     # Supports building with the version of clang shipped with Xcode when
     # targeting iOS by not respecting clang_base_path.
     if (toolchain_uses_xcode_clang) {
       prefix = invoker.bin_path
     } else {
       prefix = rebase_path("$clang_base_path/bin/", root_build_dir)
     }

     _cc = "${prefix}clang"
     _cxx = "${prefix}clang++"

     swiftmodule_switch = "-Wl,-add_ast_path,"

     # Compute the compiler prefix.
     if (toolchain_uses_goma) {
       assert(toolchain_cc_wrapper == "",
              "Goma and cc_wrapper can't be used together.")
       compiler_prefix = "$goma_dir/gomacc "
     } else if (toolchain_cc_wrapper != "") {
       compiler_prefix = toolchain_cc_wrapper + " "
     } else {
       compiler_prefix = ""
     }

     cc = compiler_prefix + _cc
     cxx = compiler_prefix + _cxx
     ld = _cxx

     # Set the explicit search path for clang++ so it uses the right linker
     # binary.
     if (!use_lld) {
       ld += " -B " + invoker.bin_path
     }

     if (defined(toolchain_args.coverage_instrumentation_input_file)) {
       toolchain_coverage_instrumentation_input_file =
           toolchain_args.coverage_instrumentation_input_file
     } else {
       toolchain_coverage_instrumentation_input_file =
           coverage_instrumentation_input_file
     }
     _use_clang_coverage_wrapper =
         toolchain_coverage_instrumentation_input_file != ""
     if (_use_clang_coverage_wrapper) {
       _coverage_wrapper =
           rebase_path("//build/toolchain/clang_code_coverage_wrapper.py",
                       root_build_dir) + " --files-to-instrument=" +
           rebase_path(toolchain_coverage_instrumentation_input_file,
                       root_build_dir) + " --target-os=" + target_os
       cc = "$python_path $_coverage_wrapper ${cc}"
       cxx = "$python_path $_coverage_wrapper ${cxx}"
     }

     linker_driver =
         "TOOL_VERSION=${tool_versions.linker_driver} " +
         rebase_path("//build/toolchain/apple/linker_driver.py", root_build_dir)

     # Specify an explicit path for the strip binary.
     _strippath = invoker.bin_path + "strip"
     linker_driver += " -Wcrl,strippath," + _strippath

     if (mac_deterministic_build) {
       linker_driver += " --deterministic"
     }

     # On iOS, the final applications are assembled using lipo (to support fat
     # builds). The correct flags are passed to the linker_driver.py script
     # directly during the lipo call. The test is against the target_os because
     # there is no need to create .dSYMs for targets compiled for the host.
     if (defined(invoker.strip_with_lipo) && invoker.strip_with_lipo) {
       _enable_dsyms = false
       _save_unstripped_output = false
     } else {
       _enable_dsyms = enable_dsyms
       _save_unstripped_output = save_unstripped_output
     }

     # Make these apply to all tools below.
     lib_switch = "-l"
     lib_dir_switch = "-L"

     # Object files go in this directory. Use label_name instead of
     # target_output_name since labels will generally have no spaces and will be
     # unique in the directory.
     object_subdir = "{{target_out_dir}}/{{label_name}}"

     # If dSYMs are enabled, this flag will be added to the link tools.
     if (_enable_dsyms) {
       dsym_switch = " -Wcrl,dsym,{{root_out_dir}} "
       dsym_switch += "-Wcrl,dsymutilpath," +
                      rebase_path("//tools/clang/dsymutil/bin/dsymutil",
                                  root_build_dir) + " "

       dsym_output_dir =
           "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.dSYM"
       dsym_output = [
         "$dsym_output_dir/Contents/Info.plist",
         "$dsym_output_dir/Contents/Resources/DWARF/" +
             "{{target_output_name}}{{output_extension}}",
       ]
     } else {
       dsym_switch = ""
     }

     if (_save_unstripped_output) {
       _unstripped_output = "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.unstripped"
     }

     tool("cc") {
       depfile = "{{output}}.d"
       precompiled_header_type = "gcc"
       command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} {{cflags}} {{cflags_c}} -c {{source}} -o {{output}}"
       depsformat = "gcc"
       description = "CC {{output}}"
       outputs = [ "$object_subdir/{{source_name_part}}.o" ]
     }

     tool("cxx") {
       depfile = "{{output}}.d"
       precompiled_header_type = "gcc"
       command = "$cxx -MMD -MF $depfile {{defines}} {{include_dirs}} {{cflags}} {{cflags_cc}} -c {{source}} -o {{output}}"
       depsformat = "gcc"
       description = "CXX {{output}}"
       outputs = [ "$object_subdir/{{source_name_part}}.o" ]
     }

     tool("asm") {
       # For GCC we can just use the C compiler to compile assembly.
       depfile = "{{output}}.d"
       command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} {{asmflags}} -c {{source}} -o {{output}}"
       depsformat = "gcc"
       description = "ASM {{output}}"
       outputs = [ "$object_subdir/{{source_name_part}}.o" ]
     }

     tool("objc") {
       depfile = "{{output}}.d"
       precompiled_header_type = "gcc"
       command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} {{framework_dirs}} {{cflags}} {{cflags_objc}} -c {{source}} -o {{output}}"
       depsformat = "gcc"
       description = "OBJC {{output}}"
       outputs = [ "$object_subdir/{{source_name_part}}.o" ]
     }

     tool("objcxx") {
       depfile = "{{output}}.d"
       precompiled_header_type = "gcc"
       command = "$cxx -MMD -MF $depfile {{defines}} {{include_dirs}} {{framework_dirs}} {{cflags}} {{cflags_objcc}} -c {{source}} -o {{output}}"
       depsformat = "gcc"
       description = "OBJCXX {{output}}"
       outputs = [ "$object_subdir/{{source_name_part}}.o" ]
     }

     tool("alink") {
       rspfile = "{{output}}.rsp"

       if (!use_lld) {
         # Note about -filelist: Apple's linker reads the file list file and
         # interprets each newline-separated chunk of text as a file name. It
         # doesn't do the things one would expect from the shell like unescaping
         # or handling quotes. In contrast, when Ninja finds a file name with
         # spaces, it single-quotes them in $inputs_newline as it would normally
         # do for command-line arguments. Thus any source names with spaces, or
         # label names with spaces (which GN bases the output paths on) will be
         # corrupted by this process. Don't use spaces for source files or
         # labels.
         rspfile_content = "{{inputs_newline}}"

         script = rebase_path("//build/toolchain/apple/filter_libtool.py",
                              root_build_dir)

         # Specify explicit path for libtool.
         libtool = invoker.bin_path + "libtool"
         command = "rm -f {{output}} && TOOL_VERSION=${tool_versions.filter_libtool} $python_path $script $libtool -static -D {{arflags}} -o {{output}} -filelist $rspfile"
         description = "LIBTOOL-STATIC {{output}}"
       } else {
         rspfile_content = "{{inputs}}"
         ar = "${prefix}llvm-ar"
         command = "\"$ar\" {{arflags}} -r -c -s -D {{output}} \"@$rspfile\""

         # Remove the output file first so that ar doesn't try to modify the
         # existing file.
         command = "rm -f {{output}} && $command"
         description = "AR {{output}}"
       }
       outputs = [ "{{output_dir}}/{{target_output_name}}{{output_extension}}" ]
       default_output_dir = "{{target_out_dir}}"
       default_output_extension = ".a"
       output_prefix = "lib"
     }

     tool("solink") {
       # E.g. "./libfoo.dylib":
       dylib = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
       rspfile = dylib + ".rsp"
       pool = "//build/toolchain:link_pool($default_toolchain)"

       # These variables are not built into GN but are helpers that implement
       # (1) linking to produce a .dylib, (2) extracting the symbols from that
       # file to a temporary file, (3) if the temporary file has differences from
       # the existing .TOC file, overwrite it, otherwise, don't change it.
       #
       # As a special case, if the library reexports symbols from other dynamic
       # libraries, we always update the .TOC and skip the temporary file and
       # diffing steps, since that library always needs to be re-linked.
       tocname = dylib + ".TOC"
       temporary_tocname = dylib + ".tmp"

       # Use explicit paths to binaries. The binaries present on the default
       # search path in /usr/bin are thin wrappers around xcrun, which requires a
       # full CommandLineTools or Xcode install, and still may not choose the
       # appropriate binary if there are multiple installs.
       if (host_os == "mac") {
         nm = invoker.bin_path + "nm"
         otool = invoker.bin_path + "otool"
       } else {
         nm = "${prefix}llvm-nm"
         otool = "${prefix}llvm-otool"
       }

       does_reexport_command = "[ ! -e \"$dylib\" -o ! -e \"$tocname\" ] || $otool -l \"$dylib\" | grep -q LC_REEXPORT_DYLIB"

       link_command = "$linker_driver $ld -shared "
       if (is_component_build) {
         link_command += " -Wl,-install_name,@rpath/\"{{target_output_name}}{{output_extension}}\" "
       }
       link_command += dsym_switch
       link_command += "{{ldflags}} -o \"$dylib\" -Wl,-filelist,\"$rspfile\" {{frameworks}} {{swiftmodules}} {{solibs}} {{libs}}"

       replace_command = "if ! cmp -s \"$temporary_tocname\" \"$tocname\"; then mv \"$temporary_tocname\" \"$tocname\""
       extract_toc_command = "{ $otool -l \"$dylib\" | grep LC_ID_DYLIB -A 5; $nm -gPp \"$dylib\" | cut -f1-2 -d' ' | grep -v U\$\$; true; }"

       command = "if $does_reexport_command ; then $link_command && $extract_toc_command > \"$tocname\"; else $link_command && $extract_toc_command > \"$temporary_tocname\" && $replace_command ; fi; fi"

       rspfile_content = "{{inputs_newline}}"

       description = "SOLINK {{output}}"

       # Use this for {{output_extension}} expansions unless a target manually
       # overrides it (in which case {{output_extension}} will be what the target
       # specifies).
       default_output_dir = "{{root_out_dir}}"
       default_output_extension = ".dylib"

       output_prefix = "lib"

       # Since the above commands only updates the .TOC file when it changes, ask
       # Ninja to check if the timestamp actually changed to know if downstream
       # dependencies should be recompiled.
       restat = true

       # Tell GN about the output files. It will link to the dylib but use the
       # tocname for dependency management.
       outputs = [
         dylib,
         tocname,
       ]
       link_output = dylib
       depend_output = tocname

       if (_enable_dsyms) {
         outputs += dsym_output
       }
       if (_save_unstripped_output) {
         outputs += [ _unstripped_output ]
       }
     }

     tool("solink_module") {
       # E.g. "./libfoo.so":
       sofile = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
       rspfile = sofile + ".rsp"
       pool = "//build/toolchain:link_pool($default_toolchain)"

       link_command = "$linker_driver $ld -bundle {{ldflags}} -o \"$sofile\" -Wl,-filelist,\"$rspfile\""
       if (is_component_build) {
         link_command += " -Wl,-install_name,@rpath/{{target_output_name}}{{output_extension}}"
       }
       link_command += dsym_switch
       link_command += " {{frameworks}} {{swiftmodules}} {{solibs}} {{libs}}"
       command = link_command

       rspfile_content = "{{inputs_newline}}"

       description = "SOLINK_MODULE {{output}}"

       # Use this for {{output_extension}} expansions unless a target manually
       # overrides it (in which case {{output_extension}} will be what the target
       # specifies).
       default_output_dir = "{{root_out_dir}}"
       default_output_extension = ".so"

       outputs = [ sofile ]

       if (_enable_dsyms) {
         outputs += dsym_output
       }
       if (_save_unstripped_output) {
         outputs += [ _unstripped_output ]
       }
     }

     tool("link") {
       outfile = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
       rspfile = "$outfile.rsp"
       pool = "//build/toolchain:link_pool($default_toolchain)"

       # Note about -filelist: Apple's linker reads the file list file and
       # interprets each newline-separated chunk of text as a file name. It
       # doesn't do the things one would expect from the shell like unescaping
       # or handling quotes. In contrast, when Ninja finds a file name with
       # spaces, it single-quotes them in $inputs_newline as it would normally
       # do for command-line arguments. Thus any source names with spaces, or
       # label names with spaces (which GN bases the output paths on) will be
       # corrupted by this process. Don't use spaces for source files or labels.
       command = "$linker_driver $ld $dsym_switch {{ldflags}} -o \"$outfile\" -Wl,-filelist,\"$rspfile\" {{frameworks}} {{swiftmodules}} {{solibs}} {{libs}}"
       description = "LINK $outfile"
       rspfile_content = "{{inputs_newline}}"
       outputs = [ outfile ]

       if (_enable_dsyms) {
         outputs += dsym_output
       }
       if (_save_unstripped_output) {
         outputs += [ _unstripped_output ]
       }

       default_output_dir = "{{root_out_dir}}"
     }

     # These two are really entirely generic, but have to be repeated in
     # each toolchain because GN doesn't allow a template to be used here.
     # See //build/toolchain/toolchain.gni for details.
     tool("stamp") {
       command = stamp_command
       description = stamp_description
     }
     tool("copy") {
       command = copy_command
       description = copy_description
     }

     tool("copy_bundle_data") {
       # copy_command use hardlink if possible but this does not work with
       # directories. Also when running EG2 tests from Xcode, Xcode tries to
       # copy some files into the application bundle which fails if source
       # and destination are hardlinked together.
       #
       # Instead use clonefile to copy the files which is as efficient as
       # hardlink but ensure the file have distinct metadata (thus avoid the
       # error with ditto, see https://crbug.com/1042182).
       if (host_os == "mac") {
         command = "rm -rf {{output}} && cp -Rc {{source}} {{output}}"
       } else {
         command = "rm -rf {{output}} && cp -Rl {{source}} {{output}}"
       }
       description = "COPY_BUNDLE_DATA {{source}} {{output}}"
       pool = "//build/toolchain/apple:bundle_pool($default_toolchain)"
     }

     # Swift is only used on iOS, not macOS. We want to minimize the number
     # of Xcode-based tools used by the macOS toolchain, so we intentionally
     # disallow future uses of Swift on macOS. https://crbug.com/965663.
     if (toolchain_args.current_os == "ios") {
       tool("swift") {
         _tool = rebase_path("//build/toolchain/ios/swiftc.py", root_build_dir)

         depfile = "{{target_out_dir}}/{{module_name}}.d"
         depsformat = "gcc"

         outputs = [
           # The module needs to be the first output listed. The blank line after
           # the module is required to prevent `gn format` from changing the file
           # order.
           "{{target_gen_dir}}/{{module_name}}.swiftmodule",

           "{{target_gen_dir}}/{{module_name}}.h",
           "{{target_gen_dir}}/{{module_name}}.swiftdoc",
           "{{target_gen_dir}}/{{module_name}}.swiftsourceinfo",
         ]

         if (swift_whole_module_optimization) {
           _extra_flags = "-whole-module-optimization"
           _objects_dir = "{{target_out_dir}}"

           outputs += [ "$_objects_dir/{{module_name}}.o" ]
         } else {
           _extra_flags = ""
           _objects_dir = "{{target_out_dir}}/{{label_name}}"

           partial_outputs = [ "$_objects_dir/{{source_name_part}}.o" ]
         }

         _env_vars = "TOOL_VERSION=${tool_versions.swiftc}"
         if (invoker.sdk_developer_dir != "") {
           _env_vars += " DEVELOPER_DIR=${toolchain_args.sdk_developer_dir}"
         }

         command =
             "$_env_vars $_tool -module-name {{module_name}} " +
             "-object-dir $_objects_dir " +
             "-module-path {{target_gen_dir}}/{{module_name}}.swiftmodule " +
             "-header-path {{target_gen_dir}}/{{module_name}}.h " +
             "-depfile {{target_out_dir}}/{{module_name}}.d " +
             "-depfile-filter {{target_gen_dir}}/{{module_name}}.swiftmodule " +
             "-bridge-header {{bridge_header}} $_extra_flags " +
             "{{swiftflags}} {{include_dirs}} {{module_dirs}} {{inputs}}"
       }
     }

     # xcassets are only used on iOS, not macOS. We want to minimize the number
     # of Xcode-based tools used by the macOS toolchain, so we intentionally
     # disallow future uses of xcassets on macOS. https://crbug.com/965663.
     if (toolchain_args.current_os == "ios") {
       tool("compile_xcassets") {
         _tool = rebase_path("//build/toolchain/ios/compile_xcassets.py",
                             root_build_dir)

         command =
             "rm -f \"{{output}}\" && " +
             "TOOL_VERSION=${tool_versions.compile_xcassets} " +
             "$python_path $_tool -p \"${invoker.sdk_name}\" " +
             "-t \"${invoker.deployment_target}\" " +
             "-T \"{{bundle_product_type}}\" " +
             "-P \"{{bundle_partial_info_plist}}\" " + "-o {{output}} {{inputs}}"

         description = "COMPILE_XCASSETS {{output}}"
         pool = "//build/toolchain/apple:bundle_pool($default_toolchain)"
       }
     }

     tool("action") {
       pool = "//build/toolchain:action_pool($default_toolchain)"
     }
   }
 }
	# Copyright (c) 2013 The Chromium Authors. All rights reserved.
	# Use of this source code is governed by a BSD-style license that can be
	# found in the LICENSE file.

	# TODO(brettw) Use "gcc_toolchain.gni" like the Linux toolchains. This requires
	# some enhancements since the commands on Mac are slightly different than on
	# Linux.

	import("//build/config/apple/symbols.gni")
	import("//build/config/clang/clang.gni")
	import("//build/config/compiler/compiler.gni")
	import("//build/config/coverage/coverage.gni")
	import("//build/toolchain/cc_wrapper.gni")
	import("//build/toolchain/goma.gni")
	import("//build/toolchain/toolchain.gni")

	assert((target_os == "ios" && host_os == "mac") \|\| host_os != "win")

	declare_args() {
	# This makes the linker set timestamps in Mach-O files to 0. This isn't
	# enabled by default because this breaks Xcode's lldb. This has been fixed in
	# https://reviews.llvm.org/rL368199 but that has not yet made it into a public
	# lldb release.
	mac_deterministic_build = false

	# This controls whether whole module optimization is enabled when building
	# Swift modules. If enabled, the compiler will compile the module as one
	# unit, generating just one single object file. Otherwise, it will generate
	# one object file per .swift file. If unspecified, will default to "true"
	# for official builds, and "false" for all other builds.
	swift_whole_module_optimization = -1
	}

	if (swift_whole_module_optimization == -1) {
	swift_whole_module_optimization = is_official_build
	}

	# When implementing tools using Python scripts, a TOOL_VERSION=N env
	# variable is placed in front of the command. The N should be incremented
	# whenever the script is changed, so that the build system rebuilds all
	# edges that utilize the script. Ideally this should be changed to use
	# proper input-dirty checking, but that could be expensive. Instead, use a
	# script to get the tool scripts' modification time to use as the version.
	# This won't cause a re-generation of GN files when the tool script changes
	# but it will cause edges to be marked as dirty if the ninja files are
	# regenerated. See https://crbug.com/619083 for details. A proper fix
	# would be to have inputs to tools (https://crbug.com/621119).
	tool_versions =
	exec_script("get_tool_mtime.py",
	rebase_path([
	"//build/toolchain/apple/filter_libtool.py",
	"//build/toolchain/apple/linker_driver.py",
	"//build/toolchain/ios/compile_xcassets.py",
	"//build/toolchain/ios/swiftc.py",
	],
	root_build_dir),
	"trim scope")

	# Shared toolchain definition. Invocations should set current_os to set the
	# build args in this definition.
	template("apple_toolchain") {
	toolchain(target_name) {
	# When invoking this toolchain not as the default one, these args will be
	# passed to the build. They are ignored when this is the default toolchain.
	assert(defined(invoker.toolchain_args),
	"Toolchains must declare toolchain_args")
	toolchain_args = {
	# Populate toolchain args from the invoker.
	forward_variables_from(invoker.toolchain_args, "*")

	# The host toolchain value computed by the default toolchain's setup
	# needs to be passed through unchanged to all secondary toolchains to
	# ensure that it's always the same, regardless of the values that may be
	# set on those toolchains.
	host_toolchain = host_toolchain
	}

	# When the invoker has explicitly overridden use_goma or cc_wrapper in the
	# toolchain args, use those values, otherwise default to the global one.
	# This works because the only reasonable override that toolchains might
	# supply for these values are to force-disable them.
	if (defined(toolchain_args.use_goma)) {
	toolchain_uses_goma = toolchain_args.use_goma
	} else {
	toolchain_uses_goma = use_goma
	}
	if (defined(toolchain_args.cc_wrapper)) {
	toolchain_cc_wrapper = toolchain_args.cc_wrapper
	} else {
	toolchain_cc_wrapper = cc_wrapper
	}
	if (defined(toolchain_args.use_xcode_clang)) {
	toolchain_uses_xcode_clang = toolchain_args.use_xcode_clang
	} else {
	toolchain_uses_xcode_clang = use_xcode_clang
	}

	# Supports building with the version of clang shipped with Xcode when
	# targeting iOS by not respecting clang_base_path.
	if (toolchain_uses_xcode_clang) {
	prefix = invoker.bin_path
	} else {
	prefix = rebase_path("$clang_base_path/bin/", root_build_dir)
	}

	_cc = "${prefix}clang"
	_cxx = "${prefix}clang++"

	swiftmodule_switch = "-Wl,-add_ast_path,"

	# Compute the compiler prefix.
	if (toolchain_uses_goma) {
	assert(toolchain_cc_wrapper == "",
	"Goma and cc_wrapper can't be used together.")
	compiler_prefix = "$goma_dir/gomacc "
	} else if (toolchain_cc_wrapper != "") {
	compiler_prefix = toolchain_cc_wrapper + " "
	} else {
	compiler_prefix = ""
	}

	cc = compiler_prefix + _cc
	cxx = compiler_prefix + _cxx
	ld = _cxx

	# Set the explicit search path for clang++ so it uses the right linker
	# binary.
	if (!use_lld) {
	ld += " -B " + invoker.bin_path
	}

	if (defined(toolchain_args.coverage_instrumentation_input_file)) {
	toolchain_coverage_instrumentation_input_file =
	toolchain_args.coverage_instrumentation_input_file
	} else {
	toolchain_coverage_instrumentation_input_file =
	coverage_instrumentation_input_file
	}
	_use_clang_coverage_wrapper =
	toolchain_coverage_instrumentation_input_file != ""
	if (_use_clang_coverage_wrapper) {
	_coverage_wrapper =
	rebase_path("//build/toolchain/clang_code_coverage_wrapper.py",
	root_build_dir) + " --files-to-instrument=" +
	rebase_path(toolchain_coverage_instrumentation_input_file,
	root_build_dir) + " --target-os=" + target_os
	cc = "$python_path $_coverage_wrapper ${cc}"
	cxx = "$python_path $_coverage_wrapper ${cxx}"
	}

	linker_driver =
	"TOOL_VERSION=${tool_versions.linker_driver} " +
	rebase_path("//build/toolchain/apple/linker_driver.py", root_build_dir)

	# Specify an explicit path for the strip binary.
	_strippath = invoker.bin_path + "strip"
	linker_driver += " -Wcrl,strippath," + _strippath

	if (mac_deterministic_build) {
	linker_driver += " --deterministic"
	}

	# On iOS, the final applications are assembled using lipo (to support fat
	# builds). The correct flags are passed to the linker_driver.py script
	# directly during the lipo call. The test is against the target_os because
	# there is no need to create .dSYMs for targets compiled for the host.
	if (defined(invoker.strip_with_lipo) && invoker.strip_with_lipo) {
	_enable_dsyms = false
	_save_unstripped_output = false
	} else {
	_enable_dsyms = enable_dsyms
	_save_unstripped_output = save_unstripped_output
	}

	# Make these apply to all tools below.
	lib_switch = "-l"
	lib_dir_switch = "-L"

	# Object files go in this directory. Use label_name instead of
	# target_output_name since labels will generally have no spaces and will be
	# unique in the directory.
	object_subdir = "{{target_out_dir}}/{{label_name}}"

	# If dSYMs are enabled, this flag will be added to the link tools.
	if (_enable_dsyms) {
	dsym_switch = " -Wcrl,dsym,{{root_out_dir}} "
	dsym_switch += "-Wcrl,dsymutilpath," +
	rebase_path("//tools/clang/dsymutil/bin/dsymutil",
	root_build_dir) + " "

	dsym_output_dir =
	"{{root_out_dir}}/{{target_output_name}}{{output_extension}}.dSYM"
	dsym_output = [
	"$dsym_output_dir/Contents/Info.plist",
	"$dsym_output_dir/Contents/Resources/DWARF/" +
	"{{target_output_name}}{{output_extension}}",
	]
	} else {
	dsym_switch = ""
	}

	if (_save_unstripped_output) {
	_unstripped_output = "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.unstripped"
	}

	tool("cc") {
	depfile = "{{output}}.d"
	precompiled_header_type = "gcc"
	command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} {{cflags}} {{cflags_c}} -c {{source}} -o {{output}}"
	depsformat = "gcc"
	description = "CC {{output}}"
	outputs = [ "$object_subdir/{{source_name_part}}.o" ]
	}

	tool("cxx") {
	depfile = "{{output}}.d"
	precompiled_header_type = "gcc"
	command = "$cxx -MMD -MF $depfile {{defines}} {{include_dirs}} {{cflags}} {{cflags_cc}} -c {{source}} -o {{output}}"
	depsformat = "gcc"
	description = "CXX {{output}}"
	outputs = [ "$object_subdir/{{source_name_part}}.o" ]
	}

	tool("asm") {
	# For GCC we can just use the C compiler to compile assembly.
	depfile = "{{output}}.d"
	command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} {{asmflags}} -c {{source}} -o {{output}}"
	depsformat = "gcc"
	description = "ASM {{output}}"
	outputs = [ "$object_subdir/{{source_name_part}}.o" ]
	}

	tool("objc") {
	depfile = "{{output}}.d"
	precompiled_header_type = "gcc"
	command = "$cc -MMD -MF $depfile {{defines}} {{include_dirs}} {{framework_dirs}} {{cflags}} {{cflags_objc}} -c {{source}} -o {{output}}"
	depsformat = "gcc"
	description = "OBJC {{output}}"
	outputs = [ "$object_subdir/{{source_name_part}}.o" ]
	}

	tool("objcxx") {
	depfile = "{{output}}.d"
	precompiled_header_type = "gcc"
	command = "$cxx -MMD -MF $depfile {{defines}} {{include_dirs}} {{framework_dirs}} {{cflags}} {{cflags_objcc}} -c {{source}} -o {{output}}"
	depsformat = "gcc"
	description = "OBJCXX {{output}}"
	outputs = [ "$object_subdir/{{source_name_part}}.o" ]
	}

	tool("alink") {
	rspfile = "{{output}}.rsp"

	if (!use_lld) {
	# Note about -filelist: Apple's linker reads the file list file and
	# interprets each newline-separated chunk of text as a file name. It
	# doesn't do the things one would expect from the shell like unescaping
	# or handling quotes. In contrast, when Ninja finds a file name with
	# spaces, it single-quotes them in $inputs_newline as it would normally
	# do for command-line arguments. Thus any source names with spaces, or
	# label names with spaces (which GN bases the output paths on) will be
	# corrupted by this process. Don't use spaces for source files or
	# labels.
	rspfile_content = "{{inputs_newline}}"

	script = rebase_path("//build/toolchain/apple/filter_libtool.py",
	root_build_dir)

	# Specify explicit path for libtool.
	libtool = invoker.bin_path + "libtool"
	command = "rm -f {{output}} && TOOL_VERSION=${tool_versions.filter_libtool} $python_path $script $libtool -static -D {{arflags}} -o {{output}} -filelist $rspfile"
	description = "LIBTOOL-STATIC {{output}}"
	} else {
	rspfile_content = "{{inputs}}"
	ar = "${prefix}llvm-ar"
	command = "\"$ar\" {{arflags}} -r -c -s -D {{output}} \"@$rspfile\""

	# Remove the output file first so that ar doesn't try to modify the
	# existing file.
	command = "rm -f {{output}} && $command"
	description = "AR {{output}}"
	}
	outputs = [ "{{output_dir}}/{{target_output_name}}{{output_extension}}" ]
	default_output_dir = "{{target_out_dir}}"
	default_output_extension = ".a"
	output_prefix = "lib"
	}

	tool("solink") {
	# E.g. "./libfoo.dylib":
	dylib = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
	rspfile = dylib + ".rsp"
	pool = "//build/toolchain:link_pool($default_toolchain)"

	# These variables are not built into GN but are helpers that implement
	# (1) linking to produce a .dylib, (2) extracting the symbols from that
	# file to a temporary file, (3) if the temporary file has differences from
	# the existing .TOC file, overwrite it, otherwise, don't change it.
	#
	# As a special case, if the library reexports symbols from other dynamic
	# libraries, we always update the .TOC and skip the temporary file and
	# diffing steps, since that library always needs to be re-linked.
	tocname = dylib + ".TOC"
	temporary_tocname = dylib + ".tmp"

	# Use explicit paths to binaries. The binaries present on the default
	# search path in /usr/bin are thin wrappers around xcrun, which requires a
	# full CommandLineTools or Xcode install, and still may not choose the
	# appropriate binary if there are multiple installs.
	if (host_os == "mac") {
	nm = invoker.bin_path + "nm"
	otool = invoker.bin_path + "otool"
	} else {
	nm = "${prefix}llvm-nm"
	otool = "${prefix}llvm-otool"
	}

	does_reexport_command = "[ ! -e \"$dylib\" -o ! -e \"$tocname\" ] \|\| $otool -l \"$dylib\" \| grep -q LC_REEXPORT_DYLIB"

	link_command = "$linker_driver $ld -shared "
	if (is_component_build) {
	link_command += " -Wl,-install_name,@rpath/\"{{target_output_name}}{{output_extension}}\" "
	}
	link_command += dsym_switch
	link_command += "{{ldflags}} -o \"$dylib\" -Wl,-filelist,\"$rspfile\" {{frameworks}} {{swiftmodules}} {{solibs}} {{libs}}"

	replace_command = "if ! cmp -s \"$temporary_tocname\" \"$tocname\"; then mv \"$temporary_tocname\" \"$tocname\""
	extract_toc_command = "{ $otool -l \"$dylib\" \| grep LC_ID_DYLIB -A 5; $nm -gPp \"$dylib\" \| cut -f1-2 -d' ' \| grep -v U\$\$; true; }"

	command = "if $does_reexport_command ; then $link_command && $extract_toc_command > \"$tocname\"; else $link_command && $extract_toc_command > \"$temporary_tocname\" && $replace_command ; fi; fi"

	rspfile_content = "{{inputs_newline}}"

	description = "SOLINK {{output}}"

	# Use this for {{output_extension}} expansions unless a target manually
	# overrides it (in which case {{output_extension}} will be what the target
	# specifies).
	default_output_dir = "{{root_out_dir}}"
	default_output_extension = ".dylib"

	output_prefix = "lib"

	# Since the above commands only updates the .TOC file when it changes, ask
	# Ninja to check if the timestamp actually changed to know if downstream
	# dependencies should be recompiled.
	restat = true

	# Tell GN about the output files. It will link to the dylib but use the
	# tocname for dependency management.
	outputs = [
	dylib,
	tocname,
	]
	link_output = dylib
	depend_output = tocname

	if (_enable_dsyms) {
	outputs += dsym_output
	}
	if (_save_unstripped_output) {
	outputs += [ _unstripped_output ]
	}
	}

	tool("solink_module") {
	# E.g. "./libfoo.so":
	sofile = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
	rspfile = sofile + ".rsp"
	pool = "//build/toolchain:link_pool($default_toolchain)"

	link_command = "$linker_driver $ld -bundle {{ldflags}} -o \"$sofile\" -Wl,-filelist,\"$rspfile\""
	if (is_component_build) {
	link_command += " -Wl,-install_name,@rpath/{{target_output_name}}{{output_extension}}"
	}
	link_command += dsym_switch
	link_command += " {{frameworks}} {{swiftmodules}} {{solibs}} {{libs}}"
	command = link_command

	rspfile_content = "{{inputs_newline}}"

	description = "SOLINK_MODULE {{output}}"

	# Use this for {{output_extension}} expansions unless a target manually
	# overrides it (in which case {{output_extension}} will be what the target
	# specifies).
	default_output_dir = "{{root_out_dir}}"
	default_output_extension = ".so"

	outputs = [ sofile ]

	if (_enable_dsyms) {
	outputs += dsym_output
	}
	if (_save_unstripped_output) {
	outputs += [ _unstripped_output ]
	}
	}

	tool("link") {
	outfile = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
	rspfile = "$outfile.rsp"
	pool = "//build/toolchain:link_pool($default_toolchain)"

	# Note about -filelist: Apple's linker reads the file list file and
	# interprets each newline-separated chunk of text as a file name. It
	# doesn't do the things one would expect from the shell like unescaping
	# or handling quotes. In contrast, when Ninja finds a file name with
	# spaces, it single-quotes them in $inputs_newline as it would normally
	# do for command-line arguments. Thus any source names with spaces, or
	# label names with spaces (which GN bases the output paths on) will be
	# corrupted by this process. Don't use spaces for source files or labels.
	command = "$linker_driver $ld $dsym_switch {{ldflags}} -o \"$outfile\" -Wl,-filelist,\"$rspfile\" {{frameworks}} {{swiftmodules}} {{solibs}} {{libs}}"
	description = "LINK $outfile"
	rspfile_content = "{{inputs_newline}}"
	outputs = [ outfile ]

	if (_enable_dsyms) {
	outputs += dsym_output
	}
	if (_save_unstripped_output) {
	outputs += [ _unstripped_output ]
	}

	default_output_dir = "{{root_out_dir}}"
	}

	# These two are really entirely generic, but have to be repeated in
	# each toolchain because GN doesn't allow a template to be used here.
	# See //build/toolchain/toolchain.gni for details.
	tool("stamp") {
	command = stamp_command
	description = stamp_description
	}
	tool("copy") {
	command = copy_command
	description = copy_description
	}

	tool("copy_bundle_data") {
	# copy_command use hardlink if possible but this does not work with
	# directories. Also when running EG2 tests from Xcode, Xcode tries to
	# copy some files into the application bundle which fails if source
	# and destination are hardlinked together.
	#
	# Instead use clonefile to copy the files which is as efficient as
	# hardlink but ensure the file have distinct metadata (thus avoid the
	# error with ditto, see https://crbug.com/1042182).
	if (host_os == "mac") {
	command = "rm -rf {{output}} && cp -Rc {{source}} {{output}}"
	} else {
	command = "rm -rf {{output}} && cp -Rl {{source}} {{output}}"
	}
	description = "COPY_BUNDLE_DATA {{source}} {{output}}"
	pool = "//build/toolchain/apple:bundle_pool($default_toolchain)"
	}

	# Swift is only used on iOS, not macOS. We want to minimize the number
	# of Xcode-based tools used by the macOS toolchain, so we intentionally
	# disallow future uses of Swift on macOS. https://crbug.com/965663.
	if (toolchain_args.current_os == "ios") {
	tool("swift") {
	_tool = rebase_path("//build/toolchain/ios/swiftc.py", root_build_dir)

	depfile = "{{target_out_dir}}/{{module_name}}.d"
	depsformat = "gcc"

	outputs = [
	# The module needs to be the first output listed. The blank line after
	# the module is required to prevent `gn format` from changing the file
	# order.
	"{{target_gen_dir}}/{{module_name}}.swiftmodule",

	"{{target_gen_dir}}/{{module_name}}.h",
	"{{target_gen_dir}}/{{module_name}}.swiftdoc",
	"{{target_gen_dir}}/{{module_name}}.swiftsourceinfo",
	]

	if (swift_whole_module_optimization) {
	_extra_flags = "-whole-module-optimization"
	_objects_dir = "{{target_out_dir}}"

	outputs += [ "$_objects_dir/{{module_name}}.o" ]
	} else {
	_extra_flags = ""
	_objects_dir = "{{target_out_dir}}/{{label_name}}"

	partial_outputs = [ "$_objects_dir/{{source_name_part}}.o" ]
	}

	_env_vars = "TOOL_VERSION=${tool_versions.swiftc}"
	if (invoker.sdk_developer_dir != "") {
	_env_vars += " DEVELOPER_DIR=${toolchain_args.sdk_developer_dir}"
	}

	command =
	"$_env_vars $_tool -module-name {{module_name}} " +
	"-object-dir $_objects_dir " +
	"-module-path {{target_gen_dir}}/{{module_name}}.swiftmodule " +
	"-header-path {{target_gen_dir}}/{{module_name}}.h " +
	"-depfile {{target_out_dir}}/{{module_name}}.d " +
	"-depfile-filter {{target_gen_dir}}/{{module_name}}.swiftmodule " +
	"-bridge-header {{bridge_header}} $_extra_flags " +
	"{{swiftflags}} {{include_dirs}} {{module_dirs}} {{inputs}}"
	}
	}

	# xcassets are only used on iOS, not macOS. We want to minimize the number
	# of Xcode-based tools used by the macOS toolchain, so we intentionally
	# disallow future uses of xcassets on macOS. https://crbug.com/965663.
	if (toolchain_args.current_os == "ios") {
	tool("compile_xcassets") {
	_tool = rebase_path("//build/toolchain/ios/compile_xcassets.py",
	root_build_dir)

	command =
	"rm -f \"{{output}}\" && " +
	"TOOL_VERSION=${tool_versions.compile_xcassets} " +
	"$python_path $_tool -p \"${invoker.sdk_name}\" " +
	"-t \"${invoker.deployment_target}\" " +
	"-T \"{{bundle_product_type}}\" " +
	"-P \"{{bundle_partial_info_plist}}\" " + "-o {{output}} {{inputs}}"

	description = "COMPILE_XCASSETS {{output}}"
	pool = "//build/toolchain/apple:bundle_pool($default_toolchain)"
	}
	}

	tool("action") {
	pool = "//build/toolchain:action_pool($default_toolchain)"
	}
	}
	}