[llvm] [gn] Add clang_static_plugin_sources to link out-of-tree plugins into clang (PR #226381)

[Nico Weber via llvm-commits]

https://github.com/nico created https://github.com/llvm/llvm-project/pull/226381

This is useful for testing and profiling e.g. Chromium's clang plugins without having to export symbols from the clang binary.

  # args.gn
  clang_static_plugin_sources = [
    "/path/to/chromium/src/tools/clang/plugins/FindBadConstructsAction.cpp",
    ...
  ]
  clang_static_plugin_include_dirs = [ "/path/to/chromium/src" ]

...or put the above in a gni file and put just `import("plugins.gni")` in args.gn

No behavior change if the list is empty (the default).

>From c115ca959ab8bb22418391405a8d1bddc148677c Mon Sep 17 00:00:00 2001
From: Nico Weber <thakis at chromium.org>
Date: Sun, 20 Sep 2026 15:09:03 -0400
Subject: [PATCH] [gn] Add clang_static_plugin_sources to link out-of-tree
 plugins into clang

This is useful for testing and profiling e.g. Chromium's clang plugins
without having to export symbols from the clang binary.

  # args.gn
  clang_static_plugin_sources = [
    "/path/to/chromium/src/tools/clang/plugins/FindBadConstructsAction.cpp",
    ...
  ]
  clang_static_plugin_include_dirs = [ "/path/to/chromium/src" ]

...or put the above in a gni file and put just `import("plugins.gni")`
in args.gn

No behavior change if the list is empty (the default).
---
 .../utils/gn/secondary/clang/tools/driver/BUILD.gn | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/llvm/utils/gn/secondary/clang/tools/driver/BUILD.gn b/llvm/utils/gn/secondary/clang/tools/driver/BUILD.gn
index cd3c64256a3e6..76c6cf4f05624 100644
--- a/llvm/utils/gn/secondary/clang/tools/driver/BUILD.gn
+++ b/llvm/utils/gn/secondary/clang/tools/driver/BUILD.gn
@@ -3,6 +3,16 @@ import("//llvm/utils/gn/build/symlink_or_copy.gni")
 import("//llvm/utils/gn/build/write_cmake_config.gni")
 import("//llvm/version.gni")
 
+declare_args() {
+  # Additional source files to compile into the clang binary.
+  # This is for adding statically linked out-of-tree clang plugins.
+  # Use absolute paths ("/path/to/Plugin.cpp").
+  clang_static_plugin_sources = []
+
+  # Include directories for clang_static_plugin_sources.
+  clang_static_plugin_include_dirs = []
+}
+
 symlinks = [
   # target_name, symlink_target pairs: GN doesn't support '+' in rule names.
   [
@@ -99,5 +109,9 @@ driver_executable("clang") {
     "cc1gen_reproducer_main.cpp",
     "driver.cpp",
   ]
+  if (clang_static_plugin_sources != []) {
+    sources += clang_static_plugin_sources
+    include_dirs = clang_static_plugin_include_dirs
+  }
   needs_posix_utility_signal_handling = true
 }