[clang-tools-extra] [clang-tidy] Avoid processing declarations in system headers (PR #128150)

[via cfe-commits]

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@@ -339,6 +339,35 @@ class ClangTidyASTConsumer : public MultiplexConsumer {
   void anchor() override {};
 };
 
+/// ASTConsumer that filters top-level declarations that are in system headers,
+/// and sets the AST traversal scope to only cover the declarations in user
+/// headers. This makes all clang-tidy checks avoid spending time processing
+/// declarations in system headers. The results are discarded anyway when
+/// presenting the results.
+class IgnoreSystemHeadersConsumer : public ASTConsumer {
+public:
+  bool HandleTopLevelDecl(DeclGroupRef DG) override {
+    for (Decl *D : DG) {
+      if (!isInSystemHeader(D))
+        Decls.push_back(D);
+    }
+    return true;
+  }
+
+  void HandleTranslationUnit(ASTContext &Ctx) override {
+    Ctx.setTraversalScope(Decls);
+  }
+
+private:
+  std::vector<Decl *> Decls;
+
+  bool isInSystemHeader(Decl *D) {
+    SourceManager &SM = D->getASTContext().getSourceManager();
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EugeneZelenko wrote:

Should be `const`. Same below.

https://github.com/llvm/llvm-project/pull/128150