Optionally pass --gcc-install-dir option to clang

This option allows the selection of a particular toolchain, including
an hermetic one.

See also:
  https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-gcc-install-dir

Without this option, clang selects the latest toolchain installed on the
system, which is not necessarily the one used to build the code and can
lead to inconsistencies.

This patch is related to issue #19

Author: Synss

BUILD

@@ -33,3 +33,14 @@ label_flag(
     build_setting_default = ":clang_tidy_additional_deps_default",
     visibility = ["//visibility:public"],
 )
+
+filegroup(
+    name = "clang_tidy_gcc_install_dir_default",
+    srcs = [],
+)
+
+label_flag(
+    name = "clang_tidy_gcc_install_dir",
+    build_setting_default = ":clang_tidy_gcc_install_dir_default",
+    visibility = ["//visibility:public"],
+)

README.md

@@ -85,6 +85,40 @@ build:clang-tidy --@bazel_clang_tidy//:clang_tidy_executable=@local_config_cc//:
 This aspect is not executed on external targets. To exclude other targets,
 users may tag a target with `no-clang-tidy` or `noclangtidy`.
 
+### use with non-system gcc
+
+Create a label to the installation dir of your gcc toolchain, for example with
+skylib's `directory`.
+
+```py
+# BUILD file for gcc
+load("@bazel_skylib//rules/directory:directory.bzl", "directory")
+
+package(default_visibility = ["//visibility:public"])
+
+directory(
+    name = "toolchain_root",
+    srcs = glob([
+        "lib/**",
+        "x86_64-buildroot-linux-gnu/include/**",
+    ]),
+)
+
+directory(
+    name = "x86_64-buildroot-linux-gnu",
+    srcs = ["lib/gcc/x86_64-buildroot-linux-gnu/13.3.0"],
+)
+
+```
+
+then add the toolchain as an additional dependency and set the `clang_tidy_gcc_install_dir` option
+
+```text
+build:clang-tidy --@bazel_clang_tidy//:clang_tidy_gcc_install_dir=@gcc-linux-x86_64//:x86_64-buildroot-linux-gnu
+build:clang-tidy --@bazel_clang_tidy//:clang_tidy_additional_deps=@gcc-linux-x86_64//:toolchain_root
+```
+
+
 ## Features
 
 - Run clang-tidy on any C/C++ target

clang_tidy/clang_tidy.bzl

@@ -5,6 +5,7 @@ def _run_tidy(
         ctx,
         wrapper,
         exe,
+        gcc_install_dir,
         additional_deps,
         config,
         flags,
@@ -51,6 +52,12 @@ def _run_tidy(
     # start args passed to the compiler
     args.add("--")
 
+    if len(gcc_install_dir.files.to_list()) >= 2:
+        fail("clang_tidy_gcc_install_dir must contain at most one directory")
+
+    for dir in gcc_install_dir.files.to_list():
+        args.add("--gcc-install-dir=%s" % dir.path)
+
     ctx.actions.run(
         inputs = inputs,
         outputs = [outfile],
@@ -206,6 +213,7 @@ def _clang_tidy_aspect_impl(target, ctx):
 
     wrapper = ctx.attr._clang_tidy_wrapper.files_to_run
     exe = ctx.attr._clang_tidy_executable
+    gcc_install_dir = ctx.attr._clang_tidy_gcc_install_dir
     additional_deps = ctx.attr._clang_tidy_additional_deps
     config = ctx.attr._clang_tidy_config.files.to_list()[0]
 
@@ -230,6 +238,7 @@ def _clang_tidy_aspect_impl(target, ctx):
             ctx,
             wrapper,
             exe,
+            gcc_install_dir,
             additional_deps,
             config,
             c_flags if is_c_translation_unit(src, ctx.rule.attr.tags) else cxx_flags,
@@ -253,6 +262,7 @@ clang_tidy_aspect = aspect(
         "_cc_toolchain": attr.label(default = Label("@bazel_tools//tools/cpp:current_cc_toolchain")),
         "_clang_tidy_wrapper": attr.label(default = Label("//clang_tidy:clang_tidy")),
         "_clang_tidy_executable": attr.label(default = Label("//:clang_tidy_executable")),
+        "_clang_tidy_gcc_install_dir": attr.label(default = Label("//:clang_tidy_gcc_install_dir")),
         "_clang_tidy_additional_deps": attr.label(default = Label("//:clang_tidy_additional_deps")),
         "_clang_tidy_config": attr.label(default = Label("//:clang_tidy_config")),
     },