# 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.

# NOTE: Event though this file does not directly reference clang_toolchain()
# nor zircon_toolchain(), invoking it through toolchain_template below, GN will
# refuse to compile if the template is not previously defined.
import("//build/toolchain/clang_toolchain.gni")
import("//build/toolchain/toolchain_tags.gni")
import("//build/toolchain/variant_tags.gni")
import("//build/toolchain/zircon/zircon_toolchain.gni")

# Private subroutine of variant_toolchain_suite(), below, used to instantiate
# a single variant toolchain() instance.
#
# Parameters:
#
#   toolchain_template: Name of GN template that is invoked to instantiate
#     a GN toolchain() instance.
#
#   toolchain_template_args: Scope of arguments passed to the
#     $toolchain_template() call. Note that the value of 'toolchain_variant' in
#     this scope is ignored. Instead, these values should appear in this_variant.
#
#   this_variant: Scope of variables that will appear in this variant
#     toolchain's toolchain_variant global variable.
#
#   this_invoker: The variant_toolchain_suite() call's parent invoker.
#     Only its with_shared and toolchain_args keys will be forwarded,
#     to its toolchain_variant and toolchain_args scope, respectively.
#
#   this_pic_default: Required boolean flag that is forwarded to the
#     toolchain()'s toolchain_variant scope, overriding any value from
#     this_variant, if any.
#
template("_variant_toolchain") {
  this_variant = invoker.this_variant
  this_invoker = invoker.this_invoker
  not_needed([ "this_invoker" ])

  # Every toolchain needs the global select_variant_canonical and
  # all_toolchain_variants passed down explicitly via toolchain_args.
  # See BUILDCONFIG.gn.
  pass_through_select_variant_canonical = select_variant_canonical
  pass_through_all_toolchain_variants = all_toolchain_variants

  _target_type = invoker.toolchain_template

  target(_target_type, target_name) {
    forward_variables_from(invoker.toolchain_template_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_select_variant_canonical

      all_toolchain_variants = []
      all_toolchain_variants = pass_through_all_toolchain_variants
    }
  }
}

# Defines a standard suite of toolchain variants.
#
# This creates one or more GN toolchain() instances based on the values of
# $know_variants, $universal_variants and $select_variant_canonical as
# defined in BUILDCONFIG.gn.
#
# $target_name corresponds to the name of the base toolchain, and all
# variant toolchains will have a name like ${target_name}-${variant_suffix}
#
# Parameters
#
#   toolchain_template:
#     Required: A GN template name that will be invoked to instantiate the
#     final toolchain() instance.
#
#   with_shared:
#     Optional: If these toolchains will have a "-shared" companion.
#     (Each variant toolchain has its own "-shared" companion.)
#
#   is_pic_default:
#     Optional: If these toolchains will generate PIC-friendly code by
#     default on ELF platforms. If true, this is incompatible with
#     `with_shared == true`.
#
#   toolchain_tags:
#     Optional: A list of tags applied to each toolchain instantiated in this
#     suite. See //build/toolchain/toolchain_tags.gni for the list of valid
#     values and their meaning.
#
#   exclude_variant_tags:
#     Optional: A list of variant tags that this toolchain suite should
#     *not* instantiate.
#
#   toolchain_args:
#     Optional: Scope of common variables to be set in the variant toolchains'
#     toolchain_args scope. Note that values in each selected variant's
#     toolchain_args scope will override these values.
#
#   enable_variants:
#     Optional: A list of variant names that should always be enabled,
#     independent of the content of the global `select_variant` list. This
#     should only be used for specific targets that need it, e.g. the C
#     library needs to be built with the regular as well as ASan-enabled
#     toolchains for the Fuchsia SDK.
#
# All other parameters are passed to ${toolchain_template}(). See
# clang_toolchain_instance() and zircon_toolchain_instance() for their values.
#
template("variant_toolchain_suite") {
  # Expand all_toolchain_variants into a canonicalized, list of variant specs
  # that don't have `host_only`/`target_only` but instead take the body of one
  # or the other., and have .base.
  is_host = defined(invoker.toolchain_os) && invoker.toolchain_os == host_os
  not_needed([ "is_host" ])

  is_pic_default = defined(invoker.is_pic_default) && invoker.is_pic_default
  with_shared = defined(invoker.with_shared) && invoker.with_shared
  assert(!is_pic_default || !with_shared,
         "is_pic_default and with_shared cannot be true at the same!")

  exclude_tags = []
  if (defined(invoker.exclude_variant_tags)) {
    exclude_tags = invoker.exclude_variant_tags
    _unknown_tags = exclude_tags + all_variant_tags - all_variant_tags
    assert(
        _unknown_tags == [],
        "Unknown exclude_variant_tags ${_unknown_tags} in toolchain suite definition ${target_name}")
  }

  if (defined(invoker.toolchain_tags)) {
    _unknown_tags = []
    _unknown_tags =
        invoker.toolchain_tags + all_toolchain_tags - all_toolchain_tags
    assert(
        _unknown_tags == [],
        "Unknown toolchain_tags ${_unknown_tags} in toolchain suite definition ${target_name}")
  }

  variants = []
  foreach(variant, all_toolchain_variants) {
    variants += [
      {
        base = get_label_info(":$target_name", "label_no_toolchain")

        forward_variables_from(variant,
                               "*",
                               [
                                 "host_only",
                                 "target_only",
                               ])

        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, "*")
          }
        }

        # NOTE: foreach() is used here to ensure that `unknown_tags` is not
        # recorded in the scope.
        foreach(unknown_tags, [ [] ]) {
          unknown_tags = tags + all_variant_tags - all_variant_tags
          assert(
              unknown_tags == [],
              "Unknown tags ${unknown_tags} in variant definition: ${variant}")
        }

        if (defined(invoker.toolchain_tags)) {
          tags += invoker.toolchain_tags
          tags -= invoker.toolchain_tags
          tags += invoker.toolchain_tags
        }

        # Recompute `instrumented` flag based on tags.
        instrumented = tags + [ "instrumented" ] - [ "instrumented" ] != tags
      },
    ]
  }

  # Exclude the arguments that are for us or are verboten.
  invoker_toolchain_template_args = {
    forward_variables_from(invoker,
                           "*",
                           [
                             "enable_variants",
                             "is_pic_default",
                             "toolchain_args",
                             "toolchain_template",
                             "with_shared",
                           ])
  }
  not_needed([ "invoker_toolchain_template_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
  }

  # Handle `enable_variants` here. First ensure that the list of names corresponds
  # to known variant names.
  enabled_variant_names = []
  if (defined(invoker.enable_variants) && invoker.enable_variants != []) {
    _all_variant_names = []
    foreach(variant, variants) {
      _all_variant_names += [ variant.name ]
    }

    enabled_variant_names = invoker.enable_variants
    unknown_enabled_variants =
        invoker.enable_variants + _all_variant_names - _all_variant_names
    assert(
        unknown_enabled_variants == [],
        "Unknown variant names in enable_variants argument: $unknown_enabled_variants")
  }

  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) {
          selectors_used[i] = true

          # Only use the variant if its tags allow it.
          if (variant.tags + exclude_tags - exclude_tags == variant.tags) {
            variant_used = true
          }
        } else if (selector.variant == false) {
          selectors_used[i] = true
        }
        i = i + 1
      }
    }

    # Ensure that any variant listed in invoker.enable_variants is used too.
    if (enabled_variant_names != []) {
      if (enabled_variant_names + [ variant.name ] - [ variant.name ] !=
          enabled_variant_names) {
        variant_used = true
      }
    }

    if (variant_used) {
      # Ensure that the exclude tags list is passed to toolchain_variant,
      # as it will be used in BUILDCONFIG.gn by variant_target()
      if (exclude_tags != []) {
        variant.exclude_variant_tags = exclude_tags
      }

      _variant_toolchain("${target_name}${variant.suffix}") {
        toolchain_template = invoker.toolchain_template
        toolchain_template_args = invoker_toolchain_template_args
        this_variant = variant
        this_invoker = invoker
        this_pic_default = is_pic_default
      }
      if (with_shared) {
        _variant_toolchain("${target_name}${variant.suffix}-shared") {
          toolchain_template = invoker.toolchain_template
          toolchain_template_args = {
            forward_variables_from(invoker_toolchain_template_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" ])
}