[clang-tools-extra] [clangd] Avoid invalid include-fixer fuzzy-find queries (PR #212134)

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hongtaihu wrote:

> > Now it only rejects `CXXConversionFunctionName`.
> 
> That was exactly my question. If we always reject `CXXConversionFunctionName`, might we be discarding cases that shouldn't be discarded? I gave an example earlier with `CXXConversionFunctionName` (`W.operator Something`) where including a header would have fixed the error, but it seems with this patch we would discard such a case?

  Good point. I added your example as a regression test:

    auto V = W.operator::Something();

  with `Something` indexed from `test.h`.

  The test passes and verifies that clangd still offers
  `#include "test.h"` for `Something`, so this case is not discarded by the
  patch.

https://github.com/llvm/llvm-project/pull/212134