pw_build/rust_proc_macro.gni

# Copyright 2023 The Pigweed Authors
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may not
# use this file except in compliance with the License. You may obtain a copy of
# the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations under
# the License.

import("//build_overrides/pigweed.gni")

import("$dir_pw_build/rust_library.gni")
import("$dir_pw_toolchain/toolchain_args.gni")

# Note: In general, prefer to import target_types.gni rather than this file.
#
# A wrapper for GN's built-in rust_proc_macro target, this template wraps a
# configurable target type specified by the current toolchain to be used for all
# pw_rust_proc_macro targets.
#
# Compiling procedural macros is... a bit awkward.
#
# Even though they're provided to crates that use them as if they were normal
# external crates, they're actually '.so'/'.dylib's that are compiled for the
# host machine and then linked into the compiler, so they and all their
# dependencies should be built for the host target.
#
# For more information on the features provided by this template, see the full
# docs at https://pigweed.dev/pw_build/?highlight=pw_rust_proc_macro.
template("pw_rust_proc_macro") {
  if (defined(pw_toolchain_SCOPE.rustc_macro_toolchain_name)) {
    group(target_name) {
      public_deps =
          [ ":$target_name(${pw_toolchain_SCOPE.rustc_macro_toolchain_name})" ]
    }
    not_needed(invoker, "*")
  } else if (defined(pw_toolchain_SCOPE.is_host_toolchain) &&
             pw_toolchain_SCOPE.is_host_toolchain) {
    pw_rust_library(target_name) {
      forward_variables_from(invoker, "*")

      if (!defined(rustflags)) {
        rustflags = []
      }

      rustflags += [
        "--extern",
        "proc_macro",
      ]
      underlying_target_type = "rust_proc_macro"
    }
  } else {
    assert(
        false,
        "proc_macro target ${target_name}(${pw_toolchain_SCOPE.name}) is not " +
            "a host target, please specify a host toolchain through " +
            "`rustc_macro_toolchain_name` for it to be compiled.")
  }
}