Don't require rigid alias's trait to hold #139828

compiler-errors · 2025-04-14T22:36:32Z

See test for write-up. TL;DR is that we don't need the trait bound to hold, since we enforce it during WF.

I think this is preferable to introducing (if we even could do so) a more specific hack around coroutine interiors, higher ranked types, etc, since this is just a manifestation of more pervasive issues w/ lifetime erasure in coroutines. This just doesn't manifest in the old solver b/c it doesn't try to prove T: Trait holds when rigidly projecting <T as Trait>::Assoc.

It's pretty clear that this affects quite a few traits (#139763), so I think this needs fixing.

r? lcnr

Fixes rust-lang/trait-system-refactor-initiative#177

tests/ui/traits/next-solver/coroutine-higher-ranked-rigid.rs

compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs

lcnr · 2025-04-15T05:34:26Z

tests/ui/traits/next-solver/coroutine-higher-ranked-rigid.rs

+//@ compile-flags: -Znext-solver
+//@ edition: 2024
+//@ check-pass


to my knowledge there was no existing ui test for this.

Please move this test to ui/generators or what not and also enable it for the old solver.

lcnr · 2025-04-15T05:35:39Z

It's unfortunate that this is required, but the regressions do seem serious enough that this is our only option 👍

some nits, then r=me

compiler-errors · 2025-04-16T22:13:35Z

@bors r=lcnr rollup

bors · 2025-04-16T22:14:08Z

📌 Commit bb3c981 has been approved by lcnr

It is now in the queue for this repository.

…iaskrgr Rollup of 9 pull requests Successful merges: - rust-lang#135340 (Add `explicit_extern_abis` Feature and Enforce Explicit ABIs) - rust-lang#139440 (rustc_target: RISC-V: feature addition batch 2) - rust-lang#139667 (cfi: Remove #[no_sanitize(cfi)] for extern weak functions) - rust-lang#139828 (Don't require rigid alias's trait to hold) - rust-lang#139854 (Improve parse errors for stray lifetimes in type position) - rust-lang#139889 (Clean UI tests 3 of n) - rust-lang#139894 (Fix `opt-dist` CLI flag and make it work without LLD) - rust-lang#139900 (stepping into impls for normalization is unproductive) - rust-lang#139915 (replace some #[rustc_intrinsic] usage with use of the libcore declarations) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#139828 - compiler-errors:rigid-trait, r=lcnr Don't require rigid alias's trait to hold See test for write-up. TL;DR is that we don't need the trait bound to hold, since we enforce it during WF. I think this is preferable to introducing (if we even could do so) a more specific hack around coroutine interiors, higher ranked types, etc, since this is just a manifestation of more pervasive issues w/ lifetime erasure in coroutines. This just doesn't manifest in the old solver b/c it doesn't try to prove `T: Trait` holds when rigidly projecting `<T as Trait>::Assoc`. It's pretty clear that this affects quite a few traits (rust-lang#139763), so I think this needs fixing. r? lcnr Fixes rust-lang/trait-system-refactor-initiative#177

rustbot assigned lcnr Apr 14, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Apr 14, 2025

compiler-errors commented Apr 15, 2025

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