Make alias bounds sound in the new solver (take 2) #110673
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| Some changes occurred to the core trait solver cc @rust-lang/initiative-trait-system-refactor |
| ☔ The latest upstream changes (presumably #110674) made this pull request unmergeable. Please resolve the merge conflicts. |
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lcnr reviewed May 9, 2023
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| @bors r=lcnr rollup (only affects new solver) |
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bors added a commit to rust-lang-ci/rust that referenced this pull request May 10, 2023
…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#110673 (Make alias bounds sound in the new solver (take 2)) - rust-lang#110747 (Encode types in SMIR) - rust-lang#111095 (Correctly handle associated items of a trait inside a `#[doc(hidden)]` item) - rust-lang#111381 (Keep encoding attributes for closures) - rust-lang#111408 (Fix incorrect implication of transmuting slices) - rust-lang#111410 (Switch to `EarlyBinder` for `thir_abstract_const` query) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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Make alias bounds sound in the new solver (in a way that does not require coinduction) by only considering them for projection types whose corresponding trait refs come from a param-env candidate.
That is, given
<T as Trait>::Assoc: Bound, we only really need to consider the alias bound ifT: Traitis satisfied via a param-env candidate. If it's instead satisfied, e.g., via an user provided impl candidate or a , then that impl should have a concrete type to which we could otherwise normalize<T as Trait>::Assoc, and that concrete type is then responsible to prove theBoundon it.Similar consideration is given to opaque types, since we only need to consider alias bounds if we're not in reveal-all mode, since similarly we'd be able to reveal the opaque types and prove any bounds that way.
This does not remove that hacky "eager projection replacement" logic from object bounds, which are somewhat like alias bounds. But removing this eager normalization behavior (added in #108333) would require full coinduction to be enabled. Compare to #110628, which does remove this object-bound custom logic but requires coinduction to be sound.
r? @lcnr