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🤔 user type annotations are stored in an UnordMap, so whatever's consuming it after writeback really shouldn't be depending on ordering, right? If changing the insertion order changes anything, that's pretty suspicious; I'd imagine it means something else is doing something wrong. LocalTableInContextMut::extend takes UnordItems specifically because it should be order-independent.

Also, judging by the CI failure that prompted it, the problem in #73501 looks like DefIds not being reproducible between different rustc builds, not a problem with nondeterministic iteration order. How does this address that?

I agree with dianne's analysis

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thanks for the feedback @dianne
i need to investigate this further, i will trace through and update this PR after finding the root cause or any progression in this area

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

⚠️ Warning ⚠️

• The following commits have merge commits (commits with multiple parents) in your changes. We have a no merge policy so these commits will need to be removed for this pull request to be merged.

  • 02a7477

  You can start a rebase with the following commands:

  $ # rebase
  $ git pull --rebase https://github.com/rust-lang/rust.git main
  $ git push --force-with-lease
  

@dianne @BoxyUwU
i tried to reproduce this issue locally but the generated mir remained perfectly identical across all local tests, suggesting the root cause might be architecture difference or isolated to CI environments.
and you're right this isn't a correct fix, closing this PR.