# Copyright 2016 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import("//build/config/clang/clang.gni")
import("//build/rust/config.gni")
import("//build/toolchain/ccache.gni")
import("//build/toolchain/goma.gni")

# Each toolchain must define "stamp" and "copy" tools,
# but they are always the same in every toolchain.
stamp_command = "touch {{output}}"
stamp_description = "STAMP {{output}}"

# We use link instead of copy; the way "copy" tool is being used is
# compatible with links since Ninja is tracking changes to the source.
copy_command = "ln -f {{source}} {{output}} 2>/dev/null || (rm -rf {{output}} && cp -af {{source}} {{output}})"
copy_description = "COPY {{source}} {{output}}"

# Defines a Clang-based toolchain.
#
# Parameters
#
#   toolchain_cpu
#     Required: Value of "current_cpu" inside this toolchain.
#
#   toolchain_os
#     Required: Value of "current_os" inside this toolchain.
#
#   toolchain_args
#     Optional: Scope specifying build arguments to override in this
#     toolchain context.
#     NOTE! Do not use this in the toolchain used as the default toolchain.
#     It will have no effect, and you will be confused.
#
#   use_strip
#     Required: Whether to strip binaries, leaving unstripped ones
#     in lib.unstripped and exe.unstripped subdirectories.
#
#   prefix
#     Optional: The path from which "cc", "cxx", "ar", "ld" and
#     "strip" will be found (unless overridden).  If not given,
#     prefix defaults to $clang_prefix.
#
#   cc
#   cxx
#   ar
#   ld
#   strip
#     Optional: Override default tool names.
#
#   use_ccache, use_goma
#     Optional: Override the global setting, useful to opt out of
#     ccache/goma in a particular toolchain.
#
#   deps
#     Optional: Dependencies of this toolchain.
#
#   propagates_configs
#     Optional: public_configs should escape this toolchain via deps
#
template("clang_toolchain") {
  toolchain(target_name) {
    assert(defined(invoker.toolchain_cpu),
           "clang_toolchain() must specify a \"toolchain_cpu\"")
    assert(defined(invoker.toolchain_os),
           "clang_toolchain() must specify a \"toolchain_os\"")

    compiler_prefix = ""
    if (defined(invoker.use_goma)) {
      use_goma = invoker.use_goma
    }
    if (use_goma) {
      goma_dir = rebase_path(goma_dir)
      compiler_prefix = "$goma_dir/gomacc "
    } else {
      if (defined(invoker.use_ccache)) {
        use_ccache = invoker.use_ccache
      }
      if (use_ccache) {
        compiler_prefix = "ccache "
      }
    }

    prefix = clang_prefix
    if (defined(invoker.prefix)) {
      prefix = invoker.prefix
    }

    # Set all tools to defaults
    cc = "${prefix}/clang"
    cxx = "${prefix}/clang++"
    ar = "${prefix}/llvm-ar"
    ld = cxx
    rustc = "${rustc_prefix}/rustc"

    forward_variables_from(invoker, [ "use_strip" ])
    if (use_strip) {
      if (invoker.toolchain_os == "mac") {
        strip = "xcrun strip -Sx"
      } else {
        strip = "${prefix}/llvm-objcopy"
        buildidtool = rebase_path(
                "//prebuilt/tools/buildidtool/${host_platform}/buildidtool",
                root_build_dir)
        if (output_breakpad_syms && invoker.toolchain_os == "fuchsia") {
          dump_syms = rebase_path(
                  "//prebuilt/third_party/breakpad/${host_platform}/dump_syms/dump_syms",
                  root_build_dir)

          # The breakpad module name for executables and loadable modules.
          breakpad_name = "<_>"
        }
      }
    }

    # Override any tools as requested by the invoker
    if (defined(invoker.cc)) {
      cc = invoker.cc
    }
    if (defined(invoker.cxx)) {
      cxx = invoker.cxx
    }
    forward_variables_from(invoker,
                           [
                             "ar",
                             "deps",
                             "ld",
                             "propagates_configs",
                             "strip",
                           ])

    # These library switches can apply to all tools below.
    lib_switch = "-l"
    lib_dir_switch = "-L"

    tool("cc") {
      depfile = "{{output}}.d"
      command = "$cc -MD -MF $depfile {{defines}} {{include_dirs}} {{cflags}} {{cflags_c}} -c {{source}} -o {{output}}"
      command_launcher = compiler_prefix
      depsformat = "gcc"
      description = "CC {{output}}"
      outputs =
          [ "{{source_out_dir}}/{{target_output_name}}.{{source_file_part}}.o" ]
    }

    tool("cxx") {
      depfile = "{{output}}.d"
      command = "$cxx -MD -MF $depfile {{defines}} {{include_dirs}} {{cflags}} {{cflags_cc}} -c {{source}} -o {{output}}"
      command_launcher = compiler_prefix
      depsformat = "gcc"
      description = "CXX {{output}}"
      outputs =
          [ "{{source_out_dir}}/{{target_output_name}}.{{source_file_part}}.o" ]
    }

    tool("asm") {
      depfile = "{{output}}.d"
      command = "$cc -MD -MF $depfile {{defines}} {{include_dirs}} {{asmflags}} -c {{source}} -o {{output}}"
      command_launcher = compiler_prefix
      depsformat = "gcc"
      description = "ASM {{output}}"
      outputs =
          [ "{{source_out_dir}}/{{target_output_name}}.{{source_file_part}}.o" ]
    }

    tool("objc") {
      depfile = "{{output}}.d"
      command = "$cc -MD -MF $depfile {{defines}} {{include_dirs}} {{cflags}} {{cflags_c}} {{cflags_objc}} -c {{source}} -o {{output}}"
      command_launcher = compiler_prefix
      depsformat = "gcc"
      description = "OBJC {{output}}"
      outputs =
          [ "{{source_out_dir}}/{{target_output_name}}.{{source_file_part}}.o" ]
    }

    tool("objcxx") {
      depfile = "{{output}}.d"
      command = "$cxx -MD -MF $depfile {{defines}} {{include_dirs}} {{cflags}} {{cflags_c}} {{cflags_objcc}} -c {{source}} -o {{output}}"
      command_launcher = compiler_prefix
      depsformat = "gcc"
      description = "OBJCXX {{output}}"
      outputs =
          [ "{{source_out_dir}}/{{target_output_name}}.{{source_name_part}}.o" ]
    }

    tool("rust_bin") {
      pool = "//build/rust:pool($default_toolchain)"
      outname = "{{target_output_name}}{{output_extension}}"
      outfile = "{{output_dir}}/$outname"
      depfile = "$outfile.d"
      unstripped_outfile = outfile
      command = ""
      if (use_strip) {
        unstripped_outfile = "{{output_dir}}/exe.unstripped/{{target_output_name}}{{output_extension}}"

        # TODO: see the comment below
        command += "mkdir -p {{output_dir}}/exe.unstripped && "
      }
      if (invoker.toolchain_cpu == "wasm32") {
        # default_output_extension doesn't work on binaries
        unstripped_outfile = "$unstripped_outfile.wasm"
      }

      # TODO(47565): Replacement for rustenv
      command += "{{rustenv}} $rustc --color=always --crate-name {{crate_name}} {{source}} --crate-type {{crate_type}} --emit=dep-info=$depfile,link -Zdep-info-omit-d-target {{rustflags}} -o \"$unstripped_outfile\" {{rustdeps}} {{externs}}"

      description = "RUST {{output}}"
      default_output_dir = "{{root_out_dir}}"
      outputs = [ outfile ]

      # TODO: enable this once Ninja supports multiple outputs with depfile:
      #   https://github.com/ninja-build/ninja/pull/1534
      #if (outfile != unstripped_outfile) {
      #  outputs += [ unstripped_outfile ]
      #  if (output_breakpad_syms && current_os == "fuchsia") {
      #    outputs += [ "$outfile.sym" ]
      #  }
      #}
      if (output_breakpad_syms && invoker.toolchain_os == "fuchsia" &&
          host_os != "mac") {
        command += " && $dump_syms -r -o Fuchsia \"$unstripped_outfile\" > \"$outfile.sym\""
      }
      if (use_strip) {
        if (invoker.toolchain_os == "mac") {
          command += " && $strip \"$unstripped_outfile\" -o \"$outfile\""
        } else {
          command +=
              " && $strip --strip-sections \"$unstripped_outfile\" \"$outfile\""
        }
        if (invoker.toolchain_os != "mac" && invoker.toolchain_os != "win") {
          command +=
              " && $buildidtool -build-id-dir .build-id" +
              " -stamp \"$outfile.build-id.stamp\"" + " -entry \"=$outfile\"" +
              " -entry \".debug=$unstripped_outfile\""
        }
      }
      rust_sysroot = "$rust_sysroot"
    }

    tool("rust_rlib") {
      pool = "//build/rust:pool($default_toolchain)"
      depfile = "{{output}}.d"

      # TODO(47565): Replacement for rustenv
      command = "{{rustenv}} $rustc --color=always --crate-name {{crate_name}} {{source}} --crate-type {{crate_type}} --emit=dep-info=$depfile,link -Zdep-info-omit-d-target {{rustflags}} -o {{output}} {{rustdeps}} {{externs}}"
      description = "RUST {{output}}"
      outputs =
          [ "{{output_dir}}/lib{{target_output_name}}{{output_extension}}" ]
      default_output_dir = "{{target_out_dir}}"
      default_output_extension = ".rlib"
      rust_sysroot = "$rust_sysroot"
    }

    tool("rust_staticlib") {
      pool = "//build/rust:pool($default_toolchain)"
      depfile = "{{output}}.d"

      # TODO(47565): Replacement for rustenv
      command = "{{rustenv}} $rustc --color=always --crate-name {{crate_name}} {{source}} --crate-type {{crate_type}} --emit=dep-info=$depfile,link -Zdep-info-omit-d-target {{rustflags}} -o {{output}} {{rustdeps}} {{externs}}"
      description = "RUST {{output}}"

      # TODO: enable this once Ninja supports multiple outputs with depfile:
      #   https://github.com/ninja-build/ninja/pull/1534
      #if (outfile != unstripped_outfile) {
      #  outputs += [ unstripped_outfile ]
      #}
      #if (output_breakpad_syms && current_os == "fuchsia") {
      #  outputs += [ "$outfile.sym" ]
      #  command += " && $dump_syms -r -o Fuchsia \"$unstripped_outfile\" > \"$outfile.sym\""
      #}
      outputs = [ "{{output_dir}}/{{target_output_name}}{{output_extension}}" ]
      default_output_dir = "{{target_out_dir}}"
      default_output_extension = ".a"
      output_prefix = "lib"
      rust_sysroot = "$rust_sysroot"
    }

    tool("rust_cdylib") {
      pool = "//build/rust:pool($default_toolchain)"
      depfile = "{{output}}.d"

      # TODO(47565): Replacement for rustenv
      command = "{{rustenv}} $rustc --color=always --crate-name {{crate_name}} {{source}} --crate-type {{crate_type}} --emit=dep-info=$depfile,link -Zdep-info-omit-d-target {{rustflags}} -o {{output}} {{rustdeps}} {{externs}}"
      description = "RUST {{output}}"
      outputs = [ "{{output_dir}}/{{target_output_name}}{{output_extension}}" ]
      default_output_dir = "{{target_out_dir}}"
      if (invoker.toolchain_os == "mac") {
        default_output_extension = ".dylib"
      } else if (invoker.toolchain_cpu == "wasm32") {
        default_output_extension = ".wasm"
      } else {
        default_output_extension = ".so"
      }
      output_prefix = "lib"
      rust_sysroot = "$rust_sysroot"
    }

    tool("rust_dylib") {
      pool = "//build/rust:pool($default_toolchain)"
      outname = "{{target_output_name}}{{output_extension}}"
      outfile = "{{output_dir}}/$outname"
      depfile = "$outfile.d"
      command = ""
      if (use_strip) {
        unstripped_outfile = "{{output_dir}}/lib.unstripped/{{target_output_name}}{{output_extension}}"

        # TODO: see the comment below
        command += "mkdir -p {{output_dir}}/exe.unstripped && "
      } else {
        unstripped_outfile = outfile
      }
      command += "{{rustenv}} $rustc --color=always --crate-name {{crate_name}} {{source}} --crate-type {{crate_type}} --emit=dep-info=$depfile,link -Zdep-info-omit-d-target {{rustflags}} -o \"$unstripped_outfile\" {{rustdeps}} {{externs}}"
      description = "RUST {{output}}"
      default_output_dir = "{{root_out_dir}}"
      if (invoker.toolchain_os == "mac") {
        default_output_extension = ".dylib"
      } else if (invoker.toolchain_cpu == "wasm32") {
        default_output_extension = ".wasm"
      } else {
        default_output_extension = ".so"
      }

      output_prefix = "lib"
      outputs = [ outfile ]

      # TODO: enable this once Ninja supports multiple outputs with depfile:
      #   https://github.com/ninja-build/ninja/pull/1534
      #if (outfile != unstripped_outfile) {
      #  outputs += [ unstripped_outfile ]
      #  if (output_breakpad_syms && current_os == "fuchsia") {
      #    outputs += [ "$outfile.sym" ]
      #  }
      #}
      if (output_breakpad_syms && invoker.toolchain_os == "fuchsia") {
        command += " && $dump_syms -r -o Fuchsia \"$unstripped_outfile\" > \"$outfile.sym\""
      }
      if (use_strip) {
        if (invoker.toolchain_os == "mac") {
          command += " && $strip -x \"$unstripped_outfile\" -o \"$outfile\""
        } else {
          command +=
              " && $strip --strip-all \"$unstripped_outfile\" \"$outfile\""
        }
        if (invoker.toolchain_os != "mac" && invoker.toolchain_os != "win") {
          command +=
              " && $buildidtool -build-id-dir .build-id" +
              " -stamp \"$outfile.build-id.stamp\"" + " -entry \"=$outfile\"" +
              " -entry \".debug=$unstripped_outfile\""
        }
      }
      rust_sysroot = "$rust_sysroot"
    }

    tool("rust_macro") {
      pool = "//build/rust:pool($default_toolchain)"
      depfile = "{{output}}.d"

      # TODO(47565): Replacement for rustenv
      command = "{{rustenv}} $rustc --color=always --crate-name {{crate_name}} {{source}} --crate-type {{crate_type}} --emit=dep-info=$depfile,link -Zdep-info-omit-d-target {{rustflags}} -o {{output}} {{rustdeps}} {{externs}}"
      description = "RUST {{output}}"
      outputs = [ "{{output_dir}}/{{target_output_name}}{{output_extension}}" ]
      default_output_dir = "{{root_out_dir}}"
      if (invoker.toolchain_os == "mac") {
        default_output_extension = ".dylib"
      } else {
        default_output_extension = ".so"
      }
      output_prefix = "lib"
      rust_sysroot = "$rust_sysroot"
    }

    tool("alink") {
      rspfile = "{{output}}.rsp"
      command =
          "rm -f {{output}} && $ar {{arflags}} rcsD {{output}} @\"$rspfile\""
      description = "AR {{output}}"
      rspfile_content = "{{inputs}}"
      outputs = [ "{{output_dir}}/{{target_output_name}}{{output_extension}}" ]
      default_output_dir = "{{target_out_dir}}"
      default_output_extension = ".a"
      output_prefix = "lib"
    }

    tool("solink") {
      outname = "{{target_output_name}}{{output_extension}}"
      outfile = "{{output_dir}}/$outname"
      rspfile = "$outfile.rsp"
      pool = "//build/toolchain:link($default_toolchain)"
      unstripped_outfile = outfile
      if (use_strip) {
        unstripped_outfile = "{{output_dir}}/lib.unstripped/{{target_output_name}}{{output_extension}}"
      }
      if (invoker.toolchain_os == "mac") {
        command = "$ld -shared {{ldflags}} -Wl,-install_name,@rpath/\"{{target_output_name}}{{output_extension}}\" -o \"$unstripped_outfile\" -Wl,-filelist,\"$rspfile\" {{libs}} {{solibs}}"
        rspfile_content = "{{inputs_newline}}"
        default_output_extension = ".dylib"
      } else {
        command = "$ld -shared {{ldflags}} -o \"$unstripped_outfile\" -Wl,--Map=\"$unstripped_outfile.map\" -Wl,-soname=\"$outname\" @\"$rspfile\" {{solibs}} {{libs}}"
        rspfile_content = "{{inputs}}"
        default_output_extension = ".so"
      }
      description = "SOLINK $outfile"
      default_output_dir = "{{root_out_dir}}"
      output_prefix = "lib"
      outputs = [ outfile ]
      if (outfile != unstripped_outfile) {
        outputs += [ unstripped_outfile ]
      }
      if (use_strip) {
        if (invoker.toolchain_os == "mac") {
          command += " && $strip -x \"$unstripped_outfile\" -o \"$outfile\""
        } else {
          command +=
              " && $strip --strip-all \"$unstripped_outfile\" \"$outfile\""
          command +=
              " && $buildidtool -build-id-dir .build-id" +
              " -stamp \"$outfile.build-id.stamp\"" + " -entry \"=$outfile\"" +
              " -entry \".debug=$unstripped_outfile\""
        }
      }
      if (output_breakpad_syms && invoker.toolchain_os == "fuchsia") {
        outputs += [ "$outfile.sym" ]
        command += " && $dump_syms -r -o Fuchsia \"$unstripped_outfile\" > \"$outfile.sym\""
      }
    }

    tool("solink_module") {
      outname = "{{target_output_name}}{{output_extension}}"
      outfile = "{{output_dir}}/$outname"
      rspfile = "$outfile.rsp"
      pool = "//build/toolchain:link($default_toolchain)"
      if (use_strip) {
        unstripped_outfile = "{{output_dir}}/lib.unstripped/{{target_output_name}}{{output_extension}}"
      } else {
        unstripped_outfile = outfile
      }
      if (invoker.toolchain_os == "mac") {
        command = "$ld -shared {{ldflags}} -o \"$unstripped_outfile\" -Wl,-filelist,\"$rspfile\" {{libs}} {{solibs}}"
        rspfile_content = "{{inputs_newline}}"
        default_output_extension = ".dylib"
      } else {
        command = "$ld -shared {{ldflags}} -o \"$unstripped_outfile\" -Wl,--Map=\"$unstripped_outfile.map\" @\"$rspfile\" {{solibs}} {{libs}}"
        rspfile_content = "{{inputs}}"
        default_output_extension = ".so"
      }
      if (use_strip) {
        if (invoker.toolchain_os == "mac") {
          command += " && $strip -x \"$unstripped_outfile\" -o \"$outfile\""
        } else {
          command +=
              " && $strip --strip-all" + " \"$unstripped_outfile\" \"$outfile\""
          command +=
              " && $buildidtool -build-id-dir .build-id" +
              " -stamp \"$outfile.build-id.stamp\"" + " -entry \"=$outfile\"" +
              " -entry \".debug=$unstripped_outfile\""
        }
      }
      outputs = []
      if (output_breakpad_syms && invoker.toolchain_os == "fuchsia") {
        outputs += [ "$outfile.sym" ]
        command += " && $dump_syms -r -n \"$breakpad_name\" -o Fuchsia \"$unstripped_outfile\" > \"$outfile.sym\""
      }
      description = "SOLINK $outfile"
      default_output_dir = "{{root_out_dir}}"
      outputs += [ outfile ]
      if (outfile != unstripped_outfile) {
        outputs += [ unstripped_outfile ]
      }
    }

    tool("link") {
      outfile = "{{output_dir}}/{{target_output_name}}{{output_extension}}"
      rspfile = "$outfile.rsp"
      pool = "//build/toolchain:link($default_toolchain)"
      unstripped_outfile = outfile
      if (use_strip) {
        unstripped_outfile = "{{output_dir}}/exe.unstripped/{{target_output_name}}{{output_extension}}"
      }
      if (invoker.toolchain_os == "mac") {
        command = "$ld {{ldflags}} -o \"$unstripped_outfile\" -Wl,-filelist,\"$rspfile\" {{solibs}} {{libs}}"
        rspfile_content = "{{inputs_newline}}"
      } else {
        command = "$ld {{ldflags}} -o \"$unstripped_outfile\" -Wl,--Map=\"$unstripped_outfile.map\" -Wl,--start-group @\"$rspfile\" {{solibs}} -Wl,--end-group {{libs}}"
        rspfile_content = "{{inputs}}"
      }
      if (use_strip) {
        if (invoker.toolchain_os == "mac") {
          command += " && $strip \"$unstripped_outfile\" -o \"$outfile\""
        } else {
          command += " && " + "$strip --strip-sections" +
                     " \"$unstripped_outfile\" \"$outfile\""

          command +=
              " && $buildidtool -build-id-dir .build-id" +
              " -stamp \"$outfile.build-id.stamp\"" + " -entry \"=$outfile\"" +
              " -entry \".debug=$unstripped_outfile\""
        }
      }
      outputs = []
      if (output_breakpad_syms && invoker.toolchain_os == "fuchsia") {
        outputs += [ "$outfile.sym" ]
        command += " && $dump_syms -r -n \"$breakpad_name\" -o Fuchsia \"$unstripped_outfile\" > \"$outfile.sym\""
      }
      description = "LINK $outfile"
      default_output_dir = "{{root_out_dir}}"
      outputs += [ outfile ]
      if (outfile != unstripped_outfile) {
        outputs += [ unstripped_outfile ]
      }
    }

    tool("stamp") {
      command = stamp_command
      description = stamp_description
    }
    tool("copy") {
      command = copy_command
      description = copy_description
    }

    # 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.
    toolchain_args = {
      current_cpu = invoker.toolchain_cpu
      current_os = invoker.toolchain_os

      # These values need to be passed through unchanged.
      target_os = target_os
      target_cpu = target_cpu

      if (defined(invoker.toolchain_args)) {
        # The invoker isn't allowed to fiddle with the essential settings.
        forward_variables_from(invoker.toolchain_args,
                               "*",
                               [
                                 "current_cpu",
                                 "current_os",
                                 "target_os",
                                 "target_cpu",
                               ])
      }
    }
  }
}

# Private subroutine of clang_toolchain_suite(), below.
template("_clang_toolchain_variant") {
  this_variant = invoker.this_variant
  this_invoker = invoker.this_invoker
  not_needed([ "this_invoker" ])

  # Every toolchain needs the global select_variant_canonical passed
  # down explicitly via toolchain_args.  See BUILDCONFIG.gn.
  pass_through_canonical = select_variant_canonical

  clang_toolchain(target_name) {
    forward_variables_from(invoker.clang_toolchain_args, "*")
    toolchain_args = {
      # GN's "can't overwrite a nonempty scope/list" rule also applies
      # to shadowing bindings in inner scopes.  Since there is always
      # a global binding of `toolchain_variant` that is being shadowed
      # here, we have to set it to the empty scope first.
      toolchain_variant = {
      }
      toolchain_variant = {
        forward_variables_from(this_variant, "*")
        is_pic_default = invoker.this_pic_default
        with_shared = this_invoker.with_shared
      }
      if (defined(this_variant.toolchain_args)) {
        forward_variables_from(this_variant.toolchain_args, "*")
      }
      if (defined(this_invoker.toolchain_args)) {
        forward_variables_from(this_invoker.toolchain_args, "*")
      }

      # See comment above.
      select_variant_canonical = []
      select_variant_canonical = pass_through_canonical
    }
  }
}

# Defines a standard suite of Clang-based toolchains.
#
# Parameters
#
#   with_shared:
#     Optional: If this toolchain will have a "-shared" companion.
#     (Each variant toolchain has its own "-shared" companion.)
#     Pre-set to true.  Set this to false if either no shared libraries
#     are used in this toolchain, or it's used to build nothing but
#     shared libraries anyway.
#
# See clang_toolchain for others.  Most parameters are just forwarded there.
#
template("clang_toolchain_suite") {
  # First get a canonicalized, flat list of variant specs that includes the
  # null variant.  Canonical variants don't have `host_only`/`target_only` but
  # instead take the body of one or the other, have [] for any missing list
  # fields, have .suffix as well as .name (or implied .name), and have .base.
  is_host = defined(invoker.toolchain_os) && invoker.toolchain_os == host_os
  not_needed([ "is_host" ])
  variants = []
  foreach(variant, [ false ] + known_variants) {
    variants += [
      {
        base = get_label_info(":$target_name", "label_no_toolchain")
        configs = []
        remove_common_configs = []
        remove_shared_configs = []
        deps = []
        instrumented = false
        if (variant == false) {
          name = ""
          suffix = ""
        } else {
          if (is_host) {
            if (defined(variant.host_only)) {
              forward_variables_from(variant.host_only, "*")
            }
          } else {
            if (defined(variant.target_only)) {
              forward_variables_from(variant.target_only, "*")
            }
          }
          forward_variables_from(variant,
                                 "*",
                                 [
                                   "host_only",
                                   "target_only",
                                 ])
          if (!defined(name)) {
            name = ""
            assert(configs != [],
                   "variant with no name must include nonempty configs")
            foreach(config, configs) {
              if (name != "") {
                name += "-"
              }
              name += get_label_info(config, "name")
            }
          }
          suffix = "-$name"
        }
      },
    ]
  }

  # Now elaborate the list with all the universal variant combinations.
  # Each universal variant becomes its own standalone variant when
  # combined with the null variant.
  # TODO(crbug.com/818525): The `+ []` works around a bug that crashes
  # GN with heap-use-after-free: the no-op `+` forces a copy of the list
  # in `variants`; without it, GN uses the same std::vector object in
  # the looping logic that it mutates in place for `variants +=`.
  foreach(variant, variants + []) {
    foreach(universal_variant, universal_variants) {
      variants += [
        {
          forward_variables_from(variant, "*", [ "toolchain_args" ])
          toolchain_args = {
            if (defined(variant.toolchain_args)) {
              forward_variables_from(variant.toolchain_args, "*")
            }
            if (defined(universal_variant.toolchain_args)) {
              forward_variables_from(universal_variant.toolchain_args, "*")
            }
          }
          if (name == "") {
            name = universal_variant.name
          } else {
            name += "-${universal_variant.name}"
          }
          suffix += "-${universal_variant.name}"
          configs += universal_variant.configs
          if (defined(universal_variant.remove_common_configs)) {
            remove_common_configs += universal_variant.remove_common_configs
          }
          if (defined(universal_variant.remove_shared_configs)) {
            remove_shared_configs += universal_variant.remove_shared_configs
          }
          if (defined(universal_variant.deps)) {
            deps += universal_variant.deps
          }
        },
      ]
    }
  }

  # Exclude the arguments that are for us or are verboten.
  invoker_clang_toolchain_args = {
    forward_variables_from(invoker,
                           "*",
                           [
                             "toolchain_args",
                             "toolchain_variant",
                             "with_shared",
                             "variants",
                           ])
  }
  not_needed([ "invoker_clang_toolchain_args" ])

  # Build up an array of boolean that's parallel to `select_variant`.
  # Below, we'll set `selectors_used[i]` to true when `select_variant[i]`
  # matches the name of some variant.
  selectors_used = []
  i = 0
  foreach(selector, select_variant_canonical) {
    selectors_used += [ false ]
    i = i + 1
  }

  foreach(variant, variants) {
    # Figure out if this variant is actually used.  Don't bother to define
    # toolchains for variants that are never used.  This cuts down on extra
    # GN processing so `gn gen` is faster.  More importantly, it ensures
    # that there isn't a toolchain defined using toolchain_args build
    # arguments whose declare_args() block hasn't been imported because
    # it's defined in a BUILD.gn file containing only configs that are
    # never referenced by any target if the variant is never selected.
    variant_used = variant.name == ""
    if (!variant_used) {
      i = 0
      foreach(selector, select_variant_canonical) {
        assert(defined(selector.variant),
               "`select_variant` clause missing `variant` field: $selector")
        if (selector.variant == variant.name) {
          variant_used = true
          selectors_used[i] = true
        } else if (selector.variant == false) {
          selectors_used[i] = true
        }
        i = i + 1
      }
    }

    if (variant_used) {
      _clang_toolchain_variant("${target_name}${variant.suffix}") {
        clang_toolchain_args = invoker_clang_toolchain_args
        this_variant = variant
        this_invoker = invoker
        this_pic_default = false
      }
      if (invoker.with_shared) {
        _clang_toolchain_variant("${target_name}${variant.suffix}-shared") {
          clang_toolchain_args = {
            forward_variables_from(invoker_clang_toolchain_args, "*")
            propagates_configs = true
          }
          this_variant = variant
          this_invoker = invoker
          this_pic_default = true
        }
      }
    }
  }

  i = 0
  foreach(selector, select_variant_canonical) {
    assert(selectors_used[i],
           "unknown variant in `select_variant` clause: ${selector}")
    i = i + 1
  }
  not_needed([ "selectors_used" ])
}

set_defaults("clang_toolchain_suite") {
  with_shared = true
}

template("clang_host_toolchain_suite") {
  clang_toolchain_suite(target_name) {
    forward_variables_from(invoker,
                           [
                             "toolchain_os",
                             "toolchain_cpu",
                           ])
    if (!defined(toolchain_cpu)) {
      toolchain_cpu = host_cpu
    }
    if (!defined(toolchain_os)) {
      toolchain_os = host_os
    }
    with_shared = false
    use_strip = true
  }
}