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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Apr 14, 2023
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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Jul 31, 2025
uniquify root goals during HIR typeck We need to rely on region identity to deal with hangs such as rust-lang/trait-system-refactor-initiative#210 and to keep the current behavior of `fn try_merge_responses`. This is a problem as borrowck starts by replacing each *occurrence* of a region with a unique inference variable. This frequently splits a single region during HIR typeck into multiple distinct regions. As we assume goals to always succeed during borrowck, relying on two occurances of a region being identical during HIR typeck causes ICE. See the now fixed examples in rust-lang/trait-system-refactor-initiative#27 and #139409. We've previously tried to avoid this issue by always *uniquifying* regions when canonicalizing goals. This prevents caching subtrees during canonicalization which resulted in hangs for very large types. People rely on such types in practice, which caused us to revert our attempt to reinstate `#[type_length_limit]` in #127670. The complete list of changes here: - #107981 - #110180 - #114117 - #130821 After more consideration, all occurrences of such large types need to happen outside of typeck/borrowck. We know this as we already walk over all types in the MIR body when replacing their regions with nll vars. This PR therefore enables us to rely on region identity inside of the trait solver by exclusively **uniquifying root goals during HIR typeck**. These are the only goals we assume to hold during borrowck. This is insufficient as type inference variables may "hide" regions we later uniquify. Because of this, we now stash proven goals which depend on inference variables in HIR typeck and reprove them after writeback. This closes rust-lang/trait-system-refactor-initiative#127. This was originally part of #144258 but I've moved it into a separate PR. While I believe we need to rely on region identity to fix the performance issues in some way, I don't know whether #144258 is the best approach to actually do so. Regardless of how we deal with the hangs however, this change is necessary and desirable regardless. r? `@compiler-errors` or `@BoxyUwU`
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uniquify root goals during HIR typeck We need to rely on region identity to deal with hangs such as rust-lang/trait-system-refactor-initiative#210 and to keep the current behavior of `fn try_merge_responses`. This is a problem as borrowck starts by replacing each *occurrence* of a region with a unique inference variable. This frequently splits a single region during HIR typeck into multiple distinct regions. As we assume goals to always succeed during borrowck, relying on two occurances of a region being identical during HIR typeck causes ICE. See the now fixed examples in rust-lang/trait-system-refactor-initiative#27 and rust-lang/rust#139409. We've previously tried to avoid this issue by always *uniquifying* regions when canonicalizing goals. This prevents caching subtrees during canonicalization which resulted in hangs for very large types. People rely on such types in practice, which caused us to revert our attempt to reinstate `#[type_length_limit]` in rust-lang/rust#127670. The complete list of changes here: - rust-lang/rust#107981 - rust-lang/rust#110180 - rust-lang/rust#114117 - rust-lang/rust#130821 After more consideration, all occurrences of such large types need to happen outside of typeck/borrowck. We know this as we already walk over all types in the MIR body when replacing their regions with nll vars. This PR therefore enables us to rely on region identity inside of the trait solver by exclusively **uniquifying root goals during HIR typeck**. These are the only goals we assume to hold during borrowck. This is insufficient as type inference variables may "hide" regions we later uniquify. Because of this, we now stash proven goals which depend on inference variables in HIR typeck and reprove them after writeback. This closes rust-lang/trait-system-refactor-initiative#127. This was originally part of rust-lang/rust#144258 but I've moved it into a separate PR. While I believe we need to rely on region identity to fix the performance issues in some way, I don't know whether rust-lang/rust#144258 is the best approach to actually do so. Regardless of how we deal with the hangs however, this change is necessary and desirable regardless. r? `@compiler-errors` or `@BoxyUwU`
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uniquify root goals during HIR typeck We need to rely on region identity to deal with hangs such as rust-lang/trait-system-refactor-initiative#210 and to keep the current behavior of `fn try_merge_responses`. This is a problem as borrowck starts by replacing each *occurrence* of a region with a unique inference variable. This frequently splits a single region during HIR typeck into multiple distinct regions. As we assume goals to always succeed during borrowck, relying on two occurances of a region being identical during HIR typeck causes ICE. See the now fixed examples in rust-lang/trait-system-refactor-initiative#27 and rust-lang/rust#139409. We've previously tried to avoid this issue by always *uniquifying* regions when canonicalizing goals. This prevents caching subtrees during canonicalization which resulted in hangs for very large types. People rely on such types in practice, which caused us to revert our attempt to reinstate `#[type_length_limit]` in rust-lang/rust#127670. The complete list of changes here: - rust-lang/rust#107981 - rust-lang/rust#110180 - rust-lang/rust#114117 - rust-lang/rust#130821 After more consideration, all occurrences of such large types need to happen outside of typeck/borrowck. We know this as we already walk over all types in the MIR body when replacing their regions with nll vars. This PR therefore enables us to rely on region identity inside of the trait solver by exclusively **uniquifying root goals during HIR typeck**. These are the only goals we assume to hold during borrowck. This is insufficient as type inference variables may "hide" regions we later uniquify. Because of this, we now stash proven goals which depend on inference variables in HIR typeck and reprove them after writeback. This closes rust-lang/trait-system-refactor-initiative#127. This was originally part of rust-lang/rust#144258 but I've moved it into a separate PR. While I believe we need to rely on region identity to fix the performance issues in some way, I don't know whether rust-lang/rust#144258 is the best approach to actually do so. Regardless of how we deal with the hangs however, this change is necessary and desirable regardless. r? `@compiler-errors` or `@BoxyUwU`
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uniquify root goals during HIR typeck We need to rely on region identity to deal with hangs such as rust-lang/trait-system-refactor-initiative#210 and to keep the current behavior of `fn try_merge_responses`. This is a problem as borrowck starts by replacing each *occurrence* of a region with a unique inference variable. This frequently splits a single region during HIR typeck into multiple distinct regions. As we assume goals to always succeed during borrowck, relying on two occurances of a region being identical during HIR typeck causes ICE. See the now fixed examples in rust-lang/trait-system-refactor-initiative#27 and rust-lang/rust#139409. We've previously tried to avoid this issue by always *uniquifying* regions when canonicalizing goals. This prevents caching subtrees during canonicalization which resulted in hangs for very large types. People rely on such types in practice, which caused us to revert our attempt to reinstate `#[type_length_limit]` in rust-lang/rust#127670. The complete list of changes here: - rust-lang/rust#107981 - rust-lang/rust#110180 - rust-lang/rust#114117 - rust-lang/rust#130821 After more consideration, all occurrences of such large types need to happen outside of typeck/borrowck. We know this as we already walk over all types in the MIR body when replacing their regions with nll vars. This PR therefore enables us to rely on region identity inside of the trait solver by exclusively **uniquifying root goals during HIR typeck**. These are the only goals we assume to hold during borrowck. This is insufficient as type inference variables may "hide" regions we later uniquify. Because of this, we now stash proven goals which depend on inference variables in HIR typeck and reprove them after writeback. This closes rust-lang/trait-system-refactor-initiative#127. This was originally part of rust-lang/rust#144258 but I've moved it into a separate PR. While I believe we need to rely on region identity to fix the performance issues in some way, I don't know whether rust-lang/rust#144258 is the best approach to actually do so. Regardless of how we deal with the hangs however, this change is necessary and desirable regardless. r? `@compiler-errors` or `@BoxyUwU`
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uniquify root goals during HIR typeck We need to rely on region identity to deal with hangs such as rust-lang/trait-system-refactor-initiative#210 and to keep the current behavior of `fn try_merge_responses`. This is a problem as borrowck starts by replacing each *occurrence* of a region with a unique inference variable. This frequently splits a single region during HIR typeck into multiple distinct regions. As we assume goals to always succeed during borrowck, relying on two occurances of a region being identical during HIR typeck causes ICE. See the now fixed examples in rust-lang/trait-system-refactor-initiative#27 and rust-lang/rust#139409. We've previously tried to avoid this issue by always *uniquifying* regions when canonicalizing goals. This prevents caching subtrees during canonicalization which resulted in hangs for very large types. People rely on such types in practice, which caused us to revert our attempt to reinstate `#[type_length_limit]` in rust-lang/rust#127670. The complete list of changes here: - rust-lang/rust#107981 - rust-lang/rust#110180 - rust-lang/rust#114117 - rust-lang/rust#130821 After more consideration, all occurrences of such large types need to happen outside of typeck/borrowck. We know this as we already walk over all types in the MIR body when replacing their regions with nll vars. This PR therefore enables us to rely on region identity inside of the trait solver by exclusively **uniquifying root goals during HIR typeck**. These are the only goals we assume to hold during borrowck. This is insufficient as type inference variables may "hide" regions we later uniquify. Because of this, we now stash proven goals which depend on inference variables in HIR typeck and reprove them after writeback. This closes rust-lang/trait-system-refactor-initiative#127. This was originally part of rust-lang/rust#144258 but I've moved it into a separate PR. While I believe we need to rely on region identity to fix the performance issues in some way, I don't know whether rust-lang/rust#144258 is the best approach to actually do so. Regardless of how we deal with the hangs however, this change is necessary and desirable regardless. r? `@compiler-errors` or `@BoxyUwU`
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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