# Copyright 2013 The Chromium Authors
# 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/config/rust.gni")
import("//build/toolchain/cc_wrapper.gni")
import("//build/toolchain/goma.gni")
import("//build/toolchain/rbe.gni")
import("//build/toolchain/toolchain.gni")
import("//build_overrides/build.gni")

# TODO(crbug.com/1370527): This import is required to detect whether the
# build is for the catalyst environment in order to disable the hermetic
# swift compiler (as it does not include support for catalyst). Remove it
# once the support is available.
if (is_ios) {
  import("//build/config/ios/config.gni")
}

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

declare_args() {
  # 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 unspecified, will use the toolchain downloaded via deps.
  swift_toolchain_path = -1
}

# TODO(crbug.com/1370527): Remove this and replace with `build_with_chromium`
# once the support for catalyst is available in the hermetic swift compiler.
_can_use_hermetic_swift =
    build_with_chromium && is_ios && target_environment != "catalyst"

if (swift_toolchain_path == -1) {
  if (_can_use_hermetic_swift) {
    # Version of the hermetic compiler. Needs to be updated when a new version of
    # the compiler is rolled to ensure that all outputs are regenerated. It must
    # be kept in sync with the `version` of `third_party/swift-toolchain` in
    # //DEPS.
    swiftc_version = "swift-5.7-release"

    # Use the hermetic swift toolchain.
    swift_toolchain_path = "//third_party/swift-toolchain/"
  } else {
    swift_toolchain_path = ""
  }
}

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. This is titled "single_apple_toolchain"
# because it makes exactly one toolchain. Callers will normally want to
# invoke instead "apple_toolchain" which may make an additional toolchain
# without sanitizers.
template("single_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

      # Similarly for the host toolchain which can be used to make .dylibs
      # that will successfully load into prebuilt tools.
      host_toolchain_no_sanitizers = host_toolchain_no_sanitizers
    }

    # 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_remoteexec)) {
      toolchain_uses_remoteexec = toolchain_args.use_remoteexec
    } else {
      toolchain_uses_remoteexec = use_remoteexec
    }
    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
    }
    assert(!(toolchain_uses_remoteexec && toolchain_uses_goma),
           "Goma and re-client can't be used together.")
    assert(!(toolchain_cc_wrapper != "" && toolchain_uses_remoteexec),
           "re-client and cc_wrapper can't be used together.")
    assert(!(toolchain_cc_wrapper != "" && toolchain_uses_goma),
           "Goma and cc_wrapper can't be used together.")

    if (defined(toolchain_args.use_lld)) {
      toolchain_uses_lld = toolchain_args.use_lld
    } else {
      toolchain_uses_lld = use_lld
    }

    # The value of all global variables (such as `is_component_build`) is the
    # one from the default toolchain when evaluating a secondary toolchain
    # (see https://crbug.com/gn/286). This mean that the value may change when
    # evaluating target/configs in the new toolchain if the variable default
    # value depends on variable set in `toolchain_args`.
    #
    # For this reason, "ios" needs to override `is_component_build` as its
    # default value depends on `current_os`. Use the overridden value if it
    # is set in `toolchain_args`.
    if (defined(toolchain_args.is_component_build)) {
      toolchain_is_component_build = toolchain_args.is_component_build
    } else {
      toolchain_is_component_build = is_component_build
    }

    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_remoteexec) {
      if (defined(toolchain_args.rbe_cc_cfg_file)) {
        toolchain_rbe_cc_cfg_file = toolchain_args.rbe_cc_cfg_file
      } else {
        toolchain_rbe_cc_cfg_file = rbe_cc_cfg_file
      }

      # C/C++ (clang) rewrapper prefix to use when use_remoteexec is true.
      compiler_prefix = "${rbe_bin_dir}/rewrapper -cfg=${toolchain_rbe_cc_cfg_file} -exec_root=${rbe_exec_root} "
    } else if (toolchain_uses_goma) {
      assert(toolchain_cc_wrapper == "",
             "Goma and cc_wrapper can't be used together.")
      compiler_prefix = "$goma_dir/gomacc "
      if (use_goma_rust) {
        rust_compiler_prefix = compiler_prefix
      }
    } 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 (!toolchain_uses_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"
    _installnametoolpath = invoker.bin_path + "install_name_tool"
    linker_driver += " -Wcrl,strippath,${_strippath} -Wcrl,installnametoolpath,${_installnametoolpath}"
    _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"
    }

    if (toolchain_has_rust) {
      if (!defined(rust_compiler_prefix)) {
        rust_compiler_prefix = ""
      }
      rustc_bin = rebase_path("${rust_sysroot}/bin/rustc", root_build_dir)
      rustc = "$rust_compiler_prefix${rustc_bin}"
      rust_sysroot_relative_to_out = rebase_path(rust_sysroot, root_out_dir)
      rustc_wrapper = rebase_path("//build/rust/rustc_wrapper.py")

      tool("rust_staticlib") {
        libname = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
        rspfile = "$libname.rsp"
        depfile = "$libname.d"

        default_output_extension = ".a"
        output_prefix = "lib"
        default_output_dir = "{{root_out_dir}}"
        description = "RUST(STATICLIB) {{output}}"
        outputs = [ libname ]

        # TODO(danakj): When `!toolchain_uses_lld` do we need to specify a path
        # to libtool like the "alink" rule?

        rspfile_content = "{{rustdeps}} {{externs}}"
        command = "\"$python_path\" \"$rustc_wrapper\" --rustc=$rustc --depfile=$depfile --rsp=$rspfile -- -Clinker=\"$_cxx\" $rustc_common_args --emit=dep-info=$depfile,link -o $libname LDFLAGS RUSTENV {{rustenv}}"
        rust_sysroot = rust_sysroot_relative_to_out
      }

      tool("rust_rlib") {
        # We must always prefix with `lib` even if the library already starts
        # with that prefix or else our stdlib is unable to find libc.rlib (or
        # actually liblibc.rlib).
        rlibname =
            "{{output_dir}}/lib{{target_output_name}}{{output_extension}}"
        depfile = "$rlibname.d"

        # Do not use rsp files in this (common) case because they occupy the
        # ninja main thread, and {{rlibs}} have shorter command lines than
        # fully linked targets.

        default_output_extension = ".rlib"

        # This is prefixed unconditionally in `rlibname`.
        # output_prefix = "lib"
        default_output_dir = "{{root_out_dir}}"
        description = "RUST {{output}}"
        outputs = [ rlibname ]

        command = "\"$python_path\" \"$rustc_wrapper\" --rustc=$rustc --depfile=$depfile -- -Clinker=\"$_cxx\" $rustc_common_args {{rustdeps}} {{externs}} --emit=dep-info=$depfile,link -o $rlibname LDFLAGS RUSTENV {{rustenv}}"
        rust_sysroot = rust_sysroot_relative_to_out
      }

      tool("rust_bin") {
        exename = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
        rspfile = "$exename.rsp"
        depfile = "$exename.d"
        pool = "//build/toolchain:link_pool($default_toolchain)"

        # TODO(danakj): solink can generate TOC files for re-exporting library
        # symbols, and we should do the same here.

        default_output_dir = "{{root_out_dir}}"
        description = "RUST(BIN) {{output}}"
        outputs = [ exename ]

        # TODO(danakj): Support dsym_switch like C++ targets.
        # link_command += dsym_switch
        # if (_enable_dsyms) {
        #   outputs += dsym_output
        # }
        # if (_save_unstripped_output) {
        #   outputs += [ _unstripped_output ]
        # }

        rspfile_content = "{{rustdeps}} {{externs}}"
        command = "\"$python_path\" \"$rustc_wrapper\" --rustc=$rustc --depfile=$depfile --rsp=$rspfile -- -Clinker=\"${_cxx}\" $rustc_common_args --emit=dep-info=$depfile,link -o $exename LDFLAGS {{ldflags}} RUSTENV {{rustenv}}"
        rust_sysroot = rust_sysroot_relative_to_out
      }

      tool("rust_cdylib") {
        dllname = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
        rspfile = "$dllname.rsp"
        depfile = "$dllname.d"
        pool = "//build/toolchain:link_pool($default_toolchain)"

        # TODO(danakj): solink can generate TOC files for re-exporting library
        # symbols, and we should do the same here.

        default_output_extension = ".dylib"
        output_prefix = "lib"
        default_output_dir = "{{root_out_dir}}"
        description = "RUST(CDYLIB) {{output}}"
        outputs = [ dllname ]

        # TODO(danakj): Support dsym_switch like C++ targets.
        # link_command += dsym_switch
        # if (_enable_dsyms) {
        #   outputs += dsym_output
        # }
        # if (_save_unstripped_output) {
        #   outputs += [ _unstripped_output ]
        # }

        rspfile_content = "{{rustdeps}} {{externs}}"
        command = "\"$python_path\" \"$rustc_wrapper\" --rustc=$rustc --depfile=$depfile --rsp=$rspfile -- -Clinker=\"${_cxx}\" $rustc_common_args --emit=dep-info=$depfile,link -o $dllname LDFLAGS {{ldflags}} RUSTENV {{rustenv}}"
        rust_sysroot = rust_sysroot_relative_to_out
      }

      tool("rust_macro") {
        dllname = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
        rspfile = "$dllname.rsp"
        depfile = "$dllname.d"
        pool = "//build/toolchain:link_pool($default_toolchain)"

        # TODO(danakj): solink can generate TOC files for re-exporting library
        # symbols, and we should do the same here.

        default_output_extension = ".dylib"
        output_prefix = "lib"
        default_output_dir = "{{root_out_dir}}"
        description = "RUST(MACRO) {{output}}"
        outputs = [ dllname ]

        # TODO(danakj): Support dsym_switch like C++ targets.
        # link_command += dsym_switch
        # if (_enable_dsyms) {
        #   outputs += dsym_output
        # }
        # if (_save_unstripped_output) {
        #   outputs += [ _unstripped_output ]
        # }

        rspfile_content = "{{rustdeps}} {{externs}}"
        command = "\"$python_path\" \"$rustc_wrapper\" --rustc=$rustc --depfile=$depfile --rsp=$rspfile -- -Clinker=\"${_cxx}\" $rustc_common_args --emit=dep-info=$depfile,link -o $dllname LDFLAGS {{ldflags}} RUSTENV {{rustenv}}"
        rust_sysroot = rust_sysroot_relative_to_out
      }
    }

    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"
      rspfile_content = "{{inputs}}"

      if (!toolchain_uses_lld) {
        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 $libtool -static -D {{arflags}} -o {{output}} @$rspfile"
        description = "LIBTOOL-STATIC {{output}}"
      } else {
        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 $ld -shared "
      if (toolchain_is_component_build) {
        link_command += " -Wl,-install_name,@rpath/\"{{target_output_name}}{{output_extension}}\" "
      }
      link_command += dsym_switch
      link_command += "{{ldflags}} -o \"$dylib\" \"@$rspfile\""

      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}} {{frameworks}} {{swiftmodules}} {{solibs}} {{libs}} {{rlibs}}"

      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\" \"@$rspfile\""
      link_command += dsym_switch
      command = link_command

      rspfile_content = "{{inputs}} {{frameworks}} {{swiftmodules}} {{solibs}} {{libs}} {{rlibs}}"

      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)"

      command = "$linker_driver $ld $dsym_switch {{ldflags}} -o \"$outfile\" \"@$rspfile\""
      description = "LINK $outfile"
      rspfile_content = "{{inputs}} {{frameworks}} {{swiftmodules}} {{solibs}} {{libs}} {{rlibs}}"
      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}} && /bin/cp -Rc {{source}} {{output}}"
      } else {
        command = "rm -rf {{output}} && /bin/cp -Rld {{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}}/{{target_output_name}}.h",
          "{{target_gen_dir}}/{{module_name}}.swiftdoc",
          "{{target_gen_dir}}/{{module_name}}.swiftsourceinfo",
        ]

        # Additional flags passed to the wrapper script but that are only
        # set conditionally.
        _extra_flags = ""

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

          outputs += [ "$_objects_dir/{{module_name}}.o" ]
        } else {
          _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}"
        }

        # Starting with version 5.6, the Swift compiler will always
        # generates precompiled headers. In anterior version, it was
        # used when bridging headers and whole module optimisation
        # where enabled, and it could be disabled with the parameter
        # `-disable-bridging-pch`.
        #
        # The precompiled headers are binary files (i.e. they are not
        # regular Objective-C header files and cannot be loaded as such).
        #
        # There is an hidden requirements that the compiler needs to
        # be told where to save those .pch files (via the parameter
        # `-pch-output-dir $dir`). If this parameter is not passed, the
        # compiler will silently write them at an incorrect location,
        # leading later pass to try to load those .pch files as either
        # regular header files (.h) or object files (.o) and causing
        # to compilation failures.
        #
        # List the directory where the precompiled header is generated
        # as an output, but do not list the .pch file itself. This is
        # because the names includes two hashes (one corresponding to
        # the compiler revision, and the other probably derived from
        # the module itself) that are difficult to generate.
        #
        # Still we want to avoid creating a directory that has the same
        # name as a file generated by another rule, so explicitly list
        # the directory in `outputs` so that gn can warn it is conflicts
        # with another output file.

        _pch_output_dir = "{{target_out_dir}}/{{module_name}}:pch/"
        outputs += [ _pch_output_dir ]

        # Include the version of the compiler on the command-line. This causes
        # `ninja` to consider all the compilation output to be dirty when the
        # version changes.
        if (defined(swiftc_version)) {
          _extra_flags += " -swiftc-version $swiftc_version"
        }

        # Include the version of Xcode on the command-line (if specified via
        # toolchain_args). This causes `ninja` to consider all the compilation
        # outputs to be dirty when the version change.
        #
        # This is required because sometimes module dependency changes between
        # different version of Xcode (e.g. when moving from Xcode 14 beta 6 to
        # Xcode 14 RC). If the swiftmodule are not rebuilt when the version
        # changes, they may encode dependency on now non-existing frameworks
        # causing linker failures ultimately.
        if (defined(toolchain_args.xcode_build)) {
          _extra_flags += " -xcode-version ${toolchain_args.xcode_build}"
        }

        if (swift_toolchain_path != "") {
          _extra_flags += " -swift-toolchain-path " +
                          rebase_path(swift_toolchain_path, root_build_dir)
        }

        # The Swift compiler assumes that the generated header will be used by
        # Objective-C code compiled with module support enabled (-fmodules).
        #
        # The import looks like this in the generated header:
        #
        #     #if __has_feature(modules)
        #     @import UIKit;
        #     #endif
        #
        # As Chromium code is compiled without support for modules (i.e. the
        # code is compiled without `-fmodules`), the dependent modules are not
        # imported from the generated header, which causes compilation failure
        # if the client code does not first import the required modules (see
        # https://crbug.com/1316061 for details).
        #
        # Secondly, clang ToT always returns `1` when `__has_features(modules)`
        # is evaluated, even if building with `-fno-modules` when building with
        # `-std=c++20` (see https://crbug.com/1284275 for details). This causes
        # the `@import` lines to be reached and the build to fail (since the
        # support for modules is not enabled).
        #
        # Instruct swiftc.py to rewrite the generated header to use the old
        # import pre-processor instructions (#import <UIKit/UIKit.h>) to work
        # around those two issues.
        _extra_flags += " -fix-module-imports"

        command =
            "$_env_vars $python_path $_tool -module-name {{module_name}} " +
            "-root-dir " + rebase_path("//", root_build_dir) + " " +
            "-object-dir $_objects_dir -pch-output-dir $_pch_output_dir " +
            "-module-path {{target_gen_dir}}/{{module_name}}.swiftmodule " +
            "-header-path {{target_gen_dir}}/{{target_output_name}}.h " +
            "-depfile {{target_out_dir}}/{{module_name}}.d " +
            "-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)

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

        command =
            "$_env_vars $python_path $_tool " +
            "-p '${toolchain_args.current_os}' " +
            "-e '${invoker.target_environment}' " +
            "-t '${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)"
    }
  }
}

# Makes a single Apple toolchain, or possibly two if we need a
# sanitizer-free equivalent.
template("apple_toolchain") {
  single_apple_toolchain(target_name) {
    assert(defined(invoker.toolchain_args),
           "Toolchains must declare toolchain_args")
    forward_variables_from(invoker,
                           "*",
                           [
                             "visibility",
                             "test_only",
                           ])

    # No need to forward visibility and test_only as they apply to targets not
    # toolchains, but presubmit checks require that we explicitly exclude them
  }

  if (using_sanitizer) {
    # Make an additional toolchain with no sanitizers.
    single_apple_toolchain("${target_name}_no_sanitizers") {
      assert(defined(invoker.toolchain_args),
             "Toolchains must declare toolchain_args")
      forward_variables_from(invoker,
                             "*",
                             [
                               "toolchain_args",
                               "visibility",
                               "test_only",
                             ])
      toolchain_args = {
        # Populate toolchain args from the invoker.
        forward_variables_from(invoker.toolchain_args, "*")
        toolchain_disables_sanitizers = true
      }
    }
  }
}