[clang] [clang-tools-extra] [clang][Serialization] Serialize DiagStateOnPushStack to fix pragma d… (PR #190420)

[via cfe-commits]

brandonxin wrote:

Hi @ChuanqiXu9 @kadircet, could you please take a look at this PR?

This fixes a bug (clangd/clangd#1167) where `#pragma clang diagnostic push` in the preamble is lost across the PCH round-trip, causing a spurious "no matching push" warning on the corresponding pop in the main file. The fix serializes/deserializes `DiagStateOnPushStack` in `WritePragmaDiagnosticMappings`/`ReadPragmaDiagnosticMappings`.

@ChuanqiXu9 - as the serialization maintainer, I'd appreciate your review on the serialization format change.
@kadircet - this directly affects clangd's preamble handling, so your input would be valuable as well.

Thanks!

https://github.com/llvm/llvm-project/pull/190420