From c2914f07316020d2da5bd425363e08f7878cd374 Mon Sep 17 00:00:00 2001
From: Matt Jolly <kangie@gentoo.org>
Date: Sun, 26 Apr 2026 20:46:34 +1000
Subject: [PATCH] Add GN overrides to configure bindgen paths for unbundled
 toolchains

This introduces 'bindgen_libclang_path', 'bindgen_clang_resource_dir',
and 'bindgen_extra_clang_args' as explicit GN arguments. When building
with an unbundled system toolchain, Linux distributions place libclang
and its associated resource headers in non-standard paths that differ
from Chromium's internal defaults.

These explicit configuration arguments allow downstream packagers to
specify the exact paths to system headers and libclang, mapping them
predictably instead of requiring hardcoded distro-specific logic within
Chromium's core GN templates.

Signed-off-by: Matt Jolly <kangie@gentoo.org>

[bentoo: rebased onto 157. M157 hoisted the libclang plumbing out of the
 two bindgen templates: rust_bindgen.gni no longer computes
 `_libclang_path` at all (its hunk is dropped), and the `-resource-dir`
 flag plus every other libclang argument now come from
 gni_impl/libclang_args.gni, which bindgen and Crubit share.  The
 resource-dir override and `bindgen_extra_clang_args` move there; the
 file imports //build/config/rust.gni for the three new args because a
 .gni import runs in a scope of its own.]
diff -ruN a/build/config/rust.gni b/build/config/rust.gni
--- a/build/config/rust.gni
+++ b/build/config/rust.gni
@@ -63,6 +63,19 @@
   # the bindgen exectuable).
   rust_bindgen_root = "//third_party/rust-toolchain"
 
+  # Directory under which to find one of `libclang.{dll,so}` (a `lib[64]` or
+  # `bin` directory containing the libclang shared library).
+  # We don't need to worry about multlib, but specify the full path here
+  # in case a distribution does.
+  bindgen_libclang_path = ""
+
+  # Directory under which to find the `clang` resource directory.
+  # This is used by bindgen to find system headers.
+  bindgen_clang_resource_dir = ""
+
+  # Additional arguments to pass to clang when running bindgen.
+  bindgen_extra_clang_args = []
+
   # If you're using a Rust toolchain as specified by rust_sysroot_absolute,
   # set this to the output of `rustc -V`. Changing this string will cause all
   # Rust targets to be rebuilt, which allows you to update your toolchain and
diff -ruN a/build/rust/gni_impl/libclang_args.gni b/build/rust/gni_impl/libclang_args.gni
--- a/build/rust/gni_impl/libclang_args.gni
+++ b/build/rust/gni_impl/libclang_args.gni
@@ -19,6 +19,7 @@
 #   }
 
 import("//build/config/clang/clang.gni")
+import("//build/config/rust.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 if (is_win) {
@@ -36,10 +37,22 @@
 # says the wrong thing. We point it to our clang's resource dir which will
 # make it behave consistently with our other command line flags and allows
 # system headers to be found.
-_libclang_extra_args += [
-  "-resource-dir",
-  rebase_path(clang_base_path + "/lib/clang/" + clang_version, root_build_dir),
-]
+if (bindgen_clang_resource_dir != "") {
+  _libclang_extra_args += [
+    "-resource-dir",
+    rebase_path(bindgen_clang_resource_dir, root_build_dir),
+  ]
+} else {
+  _libclang_extra_args += [
+    "-resource-dir",
+    rebase_path(clang_base_path + "/lib/clang/" + clang_version,
+                root_build_dir),
+  ]
+}
+
+if (bindgen_extra_clang_args != []) {
+  _libclang_extra_args += bindgen_extra_clang_args
+}
 
 if (is_win) {
   # On Windows we fall back to using system headers from a sysroot from
diff -ruN a/build/rust/rust_bindgen_generator.gni b/build/rust/rust_bindgen_generator.gni
--- a/build/rust/rust_bindgen_generator.gni
+++ b/build/rust/rust_bindgen_generator.gni
@@ -22,14 +22,18 @@
 
 # On Windows, the libclang.dll is beside the bindgen.exe, otherwise it is in
 # ../lib.
-_libclang_path = rust_bindgen_root
-if (!use_chromium_rust_toolchain &&
-    (host_cpu == "ppc64" || host_cpu == "s390x")) {
-  _libclang_path = rust_sysroot_absolute + "/lib64"
-} else if (host_os == "win") {
-  _libclang_path += "/bin"
+if (bindgen_libclang_path != "") {
+  _libclang_path = bindgen_libclang_path
 } else {
-  _libclang_path += "/lib"
+  _libclang_path = rust_bindgen_root
+  if (!use_chromium_rust_toolchain &&
+      (host_cpu == "ppc64" || host_cpu == "s390x")) {
+    _libclang_path = rust_sysroot_absolute + "/lib64"
+  } else if (host_os == "win") {
+    _libclang_path += "/bin"
+  } else {
+    _libclang_path += "/lib"
+  }
 }
 
 # Template to build Rust/C bindings with bindgen.
@@ -190,10 +194,17 @@
     if (is_linux) {
       # Linux clang, and clang libs, use a shared libstdc++, which we must
       # point to.
-      args += [
-        "--ld-library-path",
-        rebase_path(clang_base_path + "/lib", root_build_dir),
-      ]
+      if (bindgen_libclang_path != "") {
+        args += [
+          "--ld-library-path",
+          rebase_path(bindgen_libclang_path, root_build_dir),
+        ]
+      } else {
+        args += [
+          "--ld-library-path",
+          rebase_path(clang_base_path + "/lib", root_build_dir),
+        ]
+      }
     }
 
     args += [ "--bindgen-flags" ]