[clang-tools-extra] [clang-tidy] Header check support for check_clang_tidy.py (PR #175735)

[via cfe-commits]

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@@ -299,19 +367,73 @@ def check_notes(self, clang_tidy_output: str) -> None:
                 ]
             )
 
+    def check_header_messages(self, clang_tidy_output: str) -> str:
+        """
+        Filters and verifies clang-tidy diagnostics for headers.
+
+        - Input: The raw diagnostic output from clang-tidy.
+        - Output: The diagnostic output intended for the main file
+                  verification.
+
+        This function separates messages belonging to headers specified by
+        `-check-header', verifies them using FileCheck against the header's
+        own rules, and returns the rest for further processing.
+        """
+        if not self.check_headers:
+            return clang_tidy_output
+
+        header_messages: Dict[str, List[str]] = {
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EugeneZelenko wrote:

`defaultdict` should be used instead.

https://github.com/llvm/llvm-project/pull/175735