My initial reaction is that this change slows down the common case to cater to a really super pathological case; I don't think we should do it (but a benchmark could probably change my mind).
The new test needs to move from libcxx/test/std to libcxx/test/libcxx if it's testing non-mandated, libcxx-specific behavior.

Fixed requested nits

Add pretty-print test.

Looks like this breaks tests on Windows: https://buildkite.com/llvm-project/premerge-checks/builds/68330#746376c2-ce48-4ffc-b60f-515619dee28c

LGTM with some nits.

Add JSON FileSummary tests.
Add pretty-print option to llvm-readelf.

LGTM with additional comments for the tests addressed. Please also add something like [LAA] to the beginning of the title, so it is easier to categorise the change when reading the commit log.

That's not an unreasonable idea, and we did consider it, and in fact it's still on the table as something we could do. However, it's a significantly more complex change, and we're not committed to doing it, and so we wanted to at least put this warning in place to help people avoid a relatively common bug.

Add missing tests for function arguments and fix incorrect warning message for static_cast cases

Thanks for addressing my comments! I noted an oversight inline, and wonder about the intended test coverage, otherwise this looks good I think.

The ~6700 instances of // end namespace - do you observe any trend, e.g. are they concentrated in one of the LLVM sub-projects? Is it similar to the situation we have with the readability-identifier-naming check, where a number of sub-projects have disabled it in their sub-directory's .clang-tidy file?

Rebased, fixed remaining test failures.

fixed it not compiling due to a change in the lastest commits

Any luck with this?

another formatting fix

fixed problems with formatting