pw_build: Add support for rust proc macros via pw_rust_proc_macro

Change-Id: Ie5227a0afe50290e00be28284b7c3a4490d573a0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/135478
Commit-Queue: Faraaz Sareshwala <[email protected]>
Reviewed-by: Taylor Cramer <[email protected]>

BUILD.gn

@@ -411,7 +411,9 @@ group("host_tools") {
   if (pw_rust_ENABLE_EXPERIMENTAL_BUILD) {
     deps += [
       "$dir_pw_rust/examples/host_executable:hello($dir_pigweed/targets/host:host_clang_debug)",
+      "$dir_pw_rust/examples/host_executable:proc_macro($dir_pigweed/targets/host:host_clang_debug)",
       "$dir_pw_rust/examples/host_executable:test_hello($dir_pigweed/targets/host:host_clang_debug)",
+      "$dir_pw_rust/examples/host_executable:test_proc_macro($dir_pigweed/targets/host:host_clang_debug)",
     ]
   }
 }

pw_build/gn_internal/build_target.gni

@@ -85,6 +85,7 @@ template("pw_internal_build_target") {
   _builtin_target_types = [
     "executable",
     "rust_library",
+    "rust_proc_macro",
     "shared_library",
     "source_set",
     "static_library",

pw_build/rust_library.gni

@@ -56,7 +56,10 @@ template("pw_rust_library") {
       }
     }
 
-    underlying_target_type = "rust_library"
+    if (!defined(underlying_target_type)) {
+      underlying_target_type = "rust_library"
+    }
+
     crate_name = string_replace(crate_name, "-", "_")
     output_name = crate_name
     output_dir = "${target_out_dir}/lib"

pw_build/rust_proc_macro.gni

@@ -0,0 +1,32 @@
+# 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")
+
+# 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.
+#
+# 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") {
+  pw_rust_library(target_name) {
+    forward_variables_from(invoker, "*")
+    underlying_target_type = "rust_proc_macro"
+  }
+}

pw_build/target_types.gni

@@ -18,4 +18,5 @@ import("$dir_pw_build/cc_executable.gni")
 import("$dir_pw_build/cc_library.gni")
 import("$dir_pw_build/rust_executable.gni")
 import("$dir_pw_build/rust_library.gni")
+import("$dir_pw_build/rust_proc_macro.gni")
 import("$dir_pw_build/rust_test.gni")

pw_rust/examples/host_executable/BUILD.gn

@@ -54,3 +54,13 @@ pw_rust_library("c") {
   crate_root = "c/lib.rs"
   sources = [ "c/lib.rs" ]
 }
+
+pw_rust_proc_macro("proc_macro") {
+  crate_root = "proc_macro/lib.rs"
+  sources = [ "proc_macro/lib.rs" ]
+}
+
+pw_rust_test("test_proc_macro") {
+  sources = [ "proc_macro/test.rs" ]
+  deps = [ ":proc_macro" ]
+}

pw_rust/examples/host_executable/proc_macro/lib.rs

@@ -0,0 +1,21 @@
+// 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.
+
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro]
+pub fn fn_like_proc_macro(input: TokenStream) -> TokenStream {
+    input
+}

pw_rust/examples/host_executable/proc_macro/test.rs

@@ -0,0 +1,21 @@
+// 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.
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_proc_macro() {
+        proc_macro::fn_like_proc_macro!();
+    }
+}

pw_toolchain/generate_toolchain.gni

@@ -378,6 +378,14 @@ template("generate_toolchain") {
 
       _generate_rust_tools = defined(invoker.rustc)
       if (_generate_rust_tools) {
+        if (toolchain_os == "mac") {
+          _dylib_extension = ".dylib"
+        } else if (toolchain_os == "win") {
+          _dylib_extension = ".dll"
+        } else {
+          _dylib_extension = ".so"
+        }
+
         _rustc_command = string_join(
                 " ",
                 [
@@ -416,6 +424,16 @@ template("generate_toolchain") {
           command = _rustc_command
           outputs = [ _output ]
         }
+
+        tool("rust_macro") {
+          description = "rustc {{output}}"
+          default_output_dir = "{{target_out_dir}}/lib"
+          depfile = "{{output}}.d"
+          output_prefix = "lib"
+          default_output_extension = _dylib_extension
+          command = _rustc_command
+          outputs = [ _output ]
+        }
       }
     }