build/toolchain/variant_shared_library_redirect.gni

# Copyright 2020 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.

# Use this template to create a group() that redirects to a shared_library()
# target built in the appropriate build variant toolchain.
#
# This is seldom needed, typically when a non-linkable GN target needs to
# depend on a shared_library() instance directly. Let's consider the example
# of a component that contains a prebuilt ELF binary, which depends on libfdio.so
# defined by the //sdk/lib/fdio target. To achieve this, one would use something
# like the following:
#
#     variant_shared_library_redirect("my_fdio") {
#       library = "//sdk/lib/fdio"
#     }
#
#     fuchsia_component("my_component") {
#       deps = [
#         ":my_prebuilt_binary",
#         ":my_fdio",
#       ]
#       ...
#     }
#
# This ensures that the version of libfdio.so installed in the component corresponds
# to the appropriate variant selection for this build.
#
# This template should not be used for when executable(), loadable_module() or other
# linkable GN targets are defined, and depend on other shared_library() instances.
# That's because these templates perform variant selection first, to determine the
# right GN toolchain() to build them, then all their dependencies, including
# shared_library() ones, will be built in it as well.
#
# Arguments:
#   library: (required)
#     [GN label] A GN label, without toolchain, pointing to a shared_library()
#     instance.
#
#   exclude_toolchain_tags: (optional)
#     [list of strings]
#
#   extra_manifest: (optional)
#     [GN path] If specified, this must be the path to an output file to be used
#     with the extra_manifest argument of the deprecated package() template. This
#     ensures that the library will be installed into any package() that depends
#     on it. Note that creating a package with fuchsia_package() doesn't need
#     this because it relies instead on normal metadata entries to retrieve the
#     install locations of all binaries  it depends on.
#
#   output_dir, output_name, output_extension, testonly (optional)
#     [string] or [boolean]: These must match the target library's definition, if
#     it happens to set these arguments. This will ensure that variant selectors
#     based on the target's output name and testonly flag work correctly.
#
template("variant_shared_library_redirect") {
  assert(defined(invoker.library),
         "'library' must be defined when calling this template!")
  _library_label = get_label_info(invoker.library, "label_no_toolchain")
  assert(
      _library_label != get_label_info(_library_label, "label_with_toolchain"),
      "'library' label must not contain a toolchain when calling this template: $_library_label")

  # Keep this in sync with variant_target() in //build/config/BUILDCONFIG.gn
  #
  _exclude_toolchain_tags = []
  if (defined(invoker.exclude_toolchain_tags)) {
    _exclude_toolchain_tags += invoker.exclude_toolchain_tags
  }
  if (defined(toolchain_variant.exclude_variant_tags)) {
    _exclude_toolchain_tags += toolchain_variant.exclude_variant_tags
  }

  # Compute library output name, keep this in sync with shared_library()
  if (defined(invoker.output_name)) {
    _output_name = invoker.output_name
  } else {
    _output_name = get_label_info(_library_label, "name")
  }
  _prefixless = string_replace("###$_output_name", "###lib", "")
  if (_prefixless != "###$_output_name") {
    _output_name = _prefixless
  }
  if (defined(invoker.output_extension)) {
    _output_extension = invoker.output_extension
  } else {
    if (current_os == "mac") {
      _output_extension = "dylib"
    } else if (current_os == "win") {
      _output_extension = "dll"
    } else {
      _output_extension = "so"
    }
  }
  _output_name = "lib${_output_name}"
  if (_output_extension != "") {
    _output_name += "." + _output_extension
  }

  if (defined(invoker.output_dir)) {
    _output_dir = invoker.output_dir
  } else {
    _output_dir = target_out_dir
  }

  testonly = false
  forward_variables_from(invoker, [ "testonly" ])

  _select = {
    host = is_host
    testonly = testonly
    target_type = [ "shared_library" ]
    output_name = [ _output_name ]
    label = [ _library_label ]
    name = [ get_label_info(_library_label, "name") ]
    dir = [ get_label_info(_library_label, "dir") ]
    exclude_toolchain_tags = _exclude_toolchain_tags
  }

  not_needed([ "_select" ])

  _variant = false
  if (select_variant_canonical != []) {
    _selected = false

    foreach(selector, select_variant_canonical) {
      if (_variant == false) {
        _selector = {
        }
        _selector = {
          target_type = []
          output_name = []
          label = []
          name = []
          dir = []
          forward_variables_from(selector, "*")
        }

        _selected = true
        if (_selected && defined(_selector.host)) {
          _selected = _selector.host == _select.host
        }

        if (_selected && defined(_selector.testonly)) {
          _selected = _selector.testonly == _select.testonly
        }

        if (_selected && _selector.target_type != []) {
          _selected = _selector.target_type + _select.target_type -
                      _select.target_type != _selector.target_type
        }

        if (_selected && _selector.output_name != []) {
          _selected = _selector.output_name + _select.output_name -
                      _select.output_name != _selector.output_name
        }

        if (_selected && _selector.label != []) {
          _selected =
              _selector.label + _select.label - _select.label != _selector.label
        }

        if (_selected && _selector.name != []) {
          _selected =
              _selector.name + _select.name - _select.name != _selector.name
        }

        if (_selected && _selector.dir != []) {
          _selected = _selector.dir + _select.dir - _select.dir != _selector.dir
        }

        if (_selected && _select.exclude_toolchain_tags != []) {
          _selected = _select.exclude_toolchain_tags + _selector.variant_tags -
                      _selector.variant_tags == _select.exclude_toolchain_tags
        }

        if (_selected && _selector.variant != false) {
          _variant = "-${_selector.variant}"
        }
      }
    }
  }

  if (_variant == false) {
    _library_toolchain = current_toolchain
  } else {
    _library_toolchain = "${toolchain_variant.base}${_variant}"
  }

  _final_target = "${_library_label}(${_library_toolchain})"

  if (defined(invoker.output_dir)) {
    _output_dir = invoker.output_dir
  } else if (_library_toolchain == default_toolchain) {
    _output_dir =
        get_label_info("${_library_label}($shlib_toolchain)", "root_out_dir")
  } else {
    _output_dir = get_label_info(_final_target, "root_out_dir") + "-shared"
  }

  group(target_name) {
    testonly = testonly
    public_deps = [ _final_target ]
  }

  if (defined(invoker.extra_manifest)) {
    generated_file("$target_name.extra_manifest_args") {
      contents = [
        "--entry-manifest=${_final_target}",
        "--entry=lib/${_output_name}=" +
            rebase_path("${_output_dir}/${_output_name}", root_build_dir),
      ]
      deps = [ _final_target ]
      outputs = [ invoker.extra_manifest ]
    }
  }
}