Add global option to disable running clang-tidy on headers

* Commit f43f9d6 added support to run
  clang-tidy on headers. After that commit, all headers will be checked
  by clang-tidy.
* Commit f43f9d6 added a tag to make it
  possible to not run clang-tidy on specific libraries.
* For projects that only want to run clang-tidy on source files, the
  only way to disable running clang-tidy on headers is to add the above
  mentioned tag to all libraries. For large projects this requires
  changing all BUILD files. This commit adds a global option instead to
  always disable running clang-tidy on headers.

BUILD

@@ -1,3 +1,11 @@
+load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
+
+bool_flag(
+    name = "run_on_headers",
+    build_setting_default = True,
+    visibility = ["//visibility:public"],
+)
+
 filegroup(
     name = "clang_tidy_config_default",
     srcs = [

clang_tidy/clang_tidy.bzl

@@ -1,5 +1,6 @@
 load("@bazel_tools//tools/build_defs/cc:action_names.bzl", "ACTION_NAMES")
 load("@bazel_tools//tools/cpp:toolchain_utils.bzl", "find_cpp_toolchain")
+load("@bazel_skylib//rules:common_settings.bzl", "BuildSettingInfo")
 
 def _run_tidy(
         ctx,
@@ -198,6 +199,12 @@ def _clang_tidy_aspect_impl(target, ctx):
     cxx_flags = _safe_flags(_toolchain_flags(ctx, ACTION_NAMES.cpp_compile) + rule_flags) + ["-xc++"]
 
     include_headers = "no-clang-tidy-headers" not in ctx.rule.attr.tags
+
+    run_on_headers = ctx.attr._run_on_headers[BuildSettingInfo].value
+    if type(run_on_headers) == type(True):
+       if not run_on_headers:
+          include_headers = False
+
     srcs = _rule_sources(ctx, include_headers)
 
     outputs = [
@@ -229,6 +236,7 @@ clang_tidy_aspect = aspect(
         "_clang_tidy_executable": attr.label(default = Label("//:clang_tidy_executable")),
         "_clang_tidy_additional_deps": attr.label(default = Label("//:clang_tidy_additional_deps")),
         "_clang_tidy_config": attr.label(default = Label("//:clang_tidy_config")),
+        "_run_on_headers": attr.label(default = Label("//:run_on_headers")),
     },
     toolchains = ["@bazel_tools//tools/cpp:toolchain_type"],
 )