Add the generic_associated_types_extended feature #94869
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☔ The latest upstream changes (presumably #95291) made this pull request unmergeable. Please resolve the merge conflicts. |
compiler-errors
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Mar 29, 2022
| .filter(|obligation| { | ||
| let mut visitor = MaxUniverse::new(); | ||
| obligation.predicate.visit_with(&mut visitor); | ||
| visitor.max_universe() < new_universe |
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Can you leave a comment:
- saying that this is temporary/hack (or whatever you want to call it), and
- explaining what this "means" -- i.e. that this filters predicates referencing the newly replaced placeholder regions
Also, dumb question, what's the difference between visitor.max_universe() < new_universe and visitor.max_universe() <= old_universe? I guess it probably doesn't change behavior here.
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So, the new_universe here refers to the universe we just created (from the replace_bound_vars_with_placeholders). Importantly, we want to skip any obligations containing this (so <= doesn't work, because = means it contains this new_universe). Any obligations with a max universe greater than new_universe must have been created from a nested HRTB (so maybe from with a fn). These are equally weird.
visitor.max_universe() < new_universe should be the same as visitor.max_universe() <= old_universe though, since new_universe should be old_universe+1, but that's more confusing IMO.
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Updated with a comment. @bors r=compiler-errors |
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📌 Commit 4f36c94 has been approved by |
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…errors Add the generic_associated_types_extended feature Right now, this only ignore obligations that reference new placeholders in `poly_project_and_unify_type`. In the future, this might do other things, like allowing object-safe GATs. **This feature is *incomplete* and quite likely unsound. This is mostly just for testing out potential future APIs using a "relaxed" set of rules until we figure out *proper* rules.** Also drive by cleanup of adding a `ProjectAndUnifyResult` enum instead of using a `Result<Result<Option>>`. r? `@nikomatsakis`
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Darn NLL |
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@bors r=compiler-errors |
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📌 Commit 4e570a6 has been approved by |
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Rollup of 6 pull requests Successful merges: - rust-lang#93901 (Stabilize native library modifier syntax and the `whole-archive` modifier specifically) - rust-lang#94806 (Fix `cargo run tidy`) - rust-lang#94869 (Add the generic_associated_types_extended feature) - rust-lang#95011 (async: Give predictable name to binding generated from .await expressions.) - rust-lang#95251 (Reduce max hash in raw strings from u16 to u8) - rust-lang#95298 (Fix double drop of allocator in IntoIter impl of Vec) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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…r-errors Make GATs object safe under generic_associated_types_extended feature Based on rust-lang#94869 Let's say we have ```rust trait StreamingIterator { type Item<'a> where Self: 'a; } ``` And `dyn for<'a> StreamingIterator<Item<'a> = &'a i32>`. If we ask `(dyn for<'a> StreamingIterator<Item<'a> = &'a i32>): StreamingIterator`, then we have to prove that `for<'x> (&'x i32): Sized`. So, we generate *new* bound vars to subst for the GAT generics. Importantly, this doesn't fully verify that these are usable and sound. r? `@nikomatsakis`
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…errors Make GATs object safe under generic_associated_types_extended feature Based on rust-lang#94869 Let's say we have ```rust trait StreamingIterator { type Item<'a> where Self: 'a; } ``` And `dyn for<'a> StreamingIterator<Item<'a> = &'a i32>`. If we ask `(dyn for<'a> StreamingIterator<Item<'a> = &'a i32>): StreamingIterator`, then we have to prove that `for<'x> (&'x i32): Sized`. So, we generate *new* bound vars to subst for the GAT generics. Importantly, this doesn't fully verify that these are usable and sound. r? `@nikomatsakis`
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Rollup of 6 pull requests Successful merges: - rust-lang#93901 (Stabilize native library modifier syntax and the `whole-archive` modifier specifically) - rust-lang#94806 (Fix `cargo run tidy`) - rust-lang#94869 (Add the generic_associated_types_extended feature) - rust-lang#95011 (async: Give predictable name to binding generated from .await expressions.) - rust-lang#95251 (Reduce max hash in raw strings from u16 to u8) - rust-lang#95298 (Fix double drop of allocator in IntoIter impl of Vec) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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Right now, this only ignore obligations that reference new placeholders in
poly_project_and_unify_type. In the future, this might do other things, like allowing object-safe GATs.This feature is incomplete and quite likely unsound. This is mostly just for testing out potential future APIs using a "relaxed" set of rules until we figure out proper rules.
Also drive by cleanup of adding a
ProjectAndUnifyResultenum instead of using aResult<Result<Option>>.r? @nikomatsakis