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fuchsia / third_party / rust / da43826398d2d5aa7f0f1e2879af2bd80910553c
commitda43826398d2d5aa7f0f1e2879af2bd80910553c[log] [tgz]
authorMatthias Krüger <476013+matthiaskrgr@users.noreply.github.com>Thu Apr 17 17:40:27 2025 +0200
committerGitHub <noreply@github.com>Thu Apr 17 17:40:27 2025 +0200
tree792b7f08ecf4488f9e4b314dfd8961c41ff01590
parent883f9f72e87ccb6838d528d8158ea6323baacc65 [diff]
parente1936d22ed6c686bc9f2c92634fba9246bd86b9d [diff]
Rollup merge of #139774 - compiler-errors:supertrait-alias, r=lcnr

Fix replacing supertrait aliases in `ReplaceProjectionWith`

The new solver has a procedure called `predicates_for_object_candidate`, which elaborates the super-bounds and item-bounds that are required to hold for a dyn trait to implement something via a built-in object impl.

In that procedure, there is a folder called `ReplaceProjectionWith` which is responsible for replacing projections that reference `Self`, so that we don't encounter cycles when we then go on to normalize those projections in the process of proving these super-bounds.

That folder had a few problems: Firstly, it wasn't actually checking that this was a super bound originating from `Self`. Secondly, it only accounted for a *single* projection type def id, but trait objects can have multiple (i.e. `trait Foo<A, B>: Bar<A, Assoc = A> + Bar<B, Assoc = B>`).

To fix the first, it's simple enough to just add an equality check for the self ty. To fix the second, I implemented a matching step that's very similar to the `projection_may_match` check we have for upcasting, since on top of having multiple choices, we need to deal with both non-structural matches and ambiguity.

This probably lacks a bit of documentation, but I think it works pretty well.

Fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/171

r? lcnr
tree: 792b7f08ecf4488f9e4b314dfd8961c41ff01590
  1. .github/
  2. compiler/
  3. library/
  4. LICENSES/
  5. src/
  6. tests/
  7. .clang-format
  8. .editorconfig
  9. .git-blame-ignore-revs
  10. .gitattributes
  11. .gitignore
  12. .gitmodules
  13. .ignore
  14. .mailmap
  15. bootstrap.example.toml
  16. Cargo.lock
  17. Cargo.toml
  18. CODE_OF_CONDUCT.md
  19. configure
  20. CONTRIBUTING.md
  21. COPYRIGHT
  22. diff
  23. INSTALL.md
  24. LICENSE-APACHE
  25. license-metadata.json
  26. LICENSE-MIT
  27. README.md
  28. RELEASES.md
  29. REUSE.toml
  30. rust-bors.toml
  31. rustfmt.toml
  32. triagebot.toml
  33. x
  34. x.ps1
  35. x.py
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