[all-commits] [llvm/llvm-project] 0689d2: [C++20][Modules] Prevent premature calls to PassIn...

[Michael Park via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0689d23ab3089eb9920b8f5caa92e423fe3475f8
      https://github.com/llvm/llvm-project/commit/0689d23ab3089eb9920b8f5caa92e423fe3475f8
  Author: Michael Park <mcypark at gmail.com>
  Date:   2025-03-15 (Sat, 15 Mar 2025)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Serialization/ASTReader.h
    M clang/lib/Serialization/ASTReader.cpp
    M clang/lib/Serialization/ASTReaderDecl.cpp
    A clang/test/Modules/pr121245.cpp
    A clang/test/Modules/pr129982.cpp

  Log Message:
  -----------
  [C++20][Modules] Prevent premature calls to PassInterestingDeclsToConsumer() within FinishedDeserializing(). (#129982)

`ASTReader::FinishedDeserializing` uses `NumCurrentElementsDeserializing` to keep track of nested `Deserializing` RAII actions. The `FinishedDeserializing` only performs actions if it is the top-level `Deserializing` layer. This works fine in general, but there is a problematic edge case.

If a call to `redecls()` in `FinishedDeserializing` performs deserialization, we re-enter `FinishedDeserializing` while in the middle of the previous `FinishedDeserializing` call.

The known problematic part of this is that this inner `FinishedDeserializing` can go all the way to `PassInterestingDeclsToConsumer`, which operates on `PotentiallyInterestingDecls` data structure which contain decls that should be handled by the previous `FinishedDeserializing` stage.

The other shared data structures are also somewhat concerning at a high-level in that the inner `FinishedDeserializing` would be handling pending actions that are not "within its scope", but this part is not known to be problematic.

We already have a guard within `PassInterestingDeclsToConsumer` because we can end up with recursive deserialization within `PassInterestingDeclsToConsumer`. The implemented solution is to apply this guard to the portion of `FinishedDeserializing` that performs further deserialization as well. This ensures that recursive deserialization does not trigger `PassInterestingDeclsToConsumer` which may operate on entries that are not ready to be passed.



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