don't uniquify regions when canonicalizing #110180
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this test was added for rust 0.4 and doesn't test anything specific. The repro originally relied on extern functions which are now just ordinary methods. It's also a run pass test even though `main` has been commented out.
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Some changes occurred to the core trait solver cc @rust-lang/initiative-trait-system-refactor |
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@bors r+ rollup |
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Dylan-DPC
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don't uniquify regions when canonicalizing uniquifying causes a bunch of issues, most notably it causes `AliasEq(<?x as Trait<'a>>::Assoc, <?x as Trait<'a>>::Assoc)` to result in ambiguity because both `normalizes-to` paths result in ambiguity and substs equate should trivially succeed but doesn't because we uniquified `'a` to two different regions. I originally added uniquification to make it easier to deal with requirement 6 from the dev-guide: https://rustc-dev-guide.rust-lang.org/solve/trait-solving.html#requirements > ### 6. Trait solving must be (free) lifetime agnostic > > Trait solving during codegen should have the same result as during typeck. As we erase > all free regions during codegen we must not rely on them during typeck. A noteworthy example > is special behavior for `'static`. cc rust-lang/rustc-dev-guide#1671 Relying on regions being identical may cause ICE during MIR typeck, but even without this PR we can end up relying on that as type inference vars can resolve to types which contain an identical region. Let's land this and deal with any ICE that crop up as we go. Will look at this issue again before stabilization. r? `@compiler-errors`
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don't uniquify regions when canonicalizing uniquifying causes a bunch of issues, most notably it causes `AliasEq(<?x as Trait<'a>>::Assoc, <?x as Trait<'a>>::Assoc)` to result in ambiguity because both `normalizes-to` paths result in ambiguity and substs equate should trivially succeed but doesn't because we uniquified `'a` to two different regions. I originally added uniquification to make it easier to deal with requirement 6 from the dev-guide: https://rustc-dev-guide.rust-lang.org/solve/trait-solving.html#requirements > ### 6. Trait solving must be (free) lifetime agnostic > > Trait solving during codegen should have the same result as during typeck. As we erase > all free regions during codegen we must not rely on them during typeck. A noteworthy example > is special behavior for `'static`. cc rust-lang/rustc-dev-guide#1671 Relying on regions being identical may cause ICE during MIR typeck, but even without this PR we can end up relying on that as type inference vars can resolve to types which contain an identical region. Let's land this and deal with any ICE that crop up as we go. Will look at this issue again before stabilization. r? ``@compiler-errors``
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Apr 14, 2023
…iaskrgr Rollup of 9 pull requests Successful merges: - rust-lang#109225 (Clarify that RUST_MIN_STACK may be internally cached) - rust-lang#109800 (Improve safe transmute error reporting) - rust-lang#110158 (Remove obsolete test case) - rust-lang#110180 (don't uniquify regions when canonicalizing) - rust-lang#110207 (Assemble `Unpin` candidates specially for generators in new solver) - rust-lang#110276 (Remove all but one of the spans in `BoundRegionKind::BrAnon`) - rust-lang#110279 (rustdoc: Correctly handle built-in compiler proc-macros as proc-macro and not macro) - rust-lang#110298 (Cover edge cases for {f32, f64}.hypot() docs) - rust-lang#110299 (Switch to `EarlyBinder` for `impl_subject` query) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
GuillaumeGomez
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Jul 27, 2023
…lcnr Restore region uniquification in the new solver 🎉 All of the bugs that were "due" to uniquification have been settled via other means (e.g. bidirectional alias-relate, param-env incompleteness, etc). Firstly, revert the functional changes in rust-lang#110180. 😸 Secondly, we need to ignore regions when considering if a goal has changed (the "has_changed" boolean returned from `evaluate_goal`) -- otherwise, because we're doing region uniquification, we may perpetually consider a goal to be changed. See the UI test I committed for an explanation.
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uniquifying causes a bunch of issues, most notably it causes
AliasEq(<?x as Trait<'a>>::Assoc, <?x as Trait<'a>>::Assoc)to result in ambiguity because bothnormalizes-topaths result in ambiguity and substs equate should trivially succeed but doesn't because we uniquified'ato two different regions.I originally added uniquification to make it easier to deal with requirement 6 from the dev-guide: https://rustc-dev-guide.rust-lang.org/solve/trait-solving.html#requirements
cc rust-lang/rustc-dev-guide#1671
Relying on regions being identical may cause ICE during MIR typeck, but even without this PR we can end up relying on that as type inference vars can resolve to types which contain an identical region. Let's land this and deal with any ICE that crop up as we go. Will look at this issue again before stabilization.
r? @compiler-errors