Implement selection for Unsize for better coercion behavior
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Some changes occurred to the core trait solver cc @rust-lang/initiative-trait-system-refactor |
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Unsize for better coercion behavior
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| ty::TraitRef::new(tcx, goal.predicate.def_id(), [*a_last_ty, *b_last_ty]), | ||
| )); | ||
| } | ||
| _ => return Ok(None), |
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please ICE here to detect mismatches
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We cannot ICE here because this goal is selected during coercion, so we legitimately may see, e.g. [T; N]: Unsize<_> during selection.
One more point towards having a typeck and codegen mode for selection...
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Left a fixme anyways.
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☔ The latest upstream changes (presumably #113308) made this pull request unmergeable. Please resolve the merge conflicts. |
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You said r=me after nits, which I think I have addressed. @bors r=lcnr rollup (new solver) |
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Implement selection for `Unsize` for better coercion behavior In order for much of coercion to succeed, we need to be able to deal with partial ambiguity of `Unsize` traits during selection. However, I pessimistically implemented selection in the new trait solver to just bail out with ambiguity if it was a built-in impl: https://github.com/rust-lang/rust/blob/9227ff28aff55b252314076fcf21c9a66f10ac1e/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs#L126 This implements a proper "rematch" procedure for dealing with built-in `Unsize` goals, so that even if the goal is ambiguous, we are able to get nested obligations which are used in the coercion selection-like loop: https://github.com/rust-lang/rust/blob/9227ff28aff55b252314076fcf21c9a66f10ac1e/compiler/rustc_hir_typeck/src/coercion.rs#L702 Second commit just moves a `resolve_vars_if_possible` call to fix a bug where we weren't detecting a trait upcasting to occur. r? `@lcnr`
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…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#113353 (Implement selection for `Unsize` for better coercion behavior) - rust-lang#113553 (Make Placeholder, GeneratorWitness*, Infer and Error unreachable on SMIR rustc_ty_to_ty) - rust-lang#113598 (Update cargo) - rust-lang#113603 (Test simd-wide-sum for codegen error) - rust-lang#113613 (Allow to have `-` in rustdoc-json test file name) - rust-lang#113615 (llvm-wrapper: adapt for LLVM API change) - rust-lang#113616 (Fix bootstrap.py uname error) r? `@ghost` `@rustbot` modify labels: rollup
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In order for much of coercion to succeed, we need to be able to deal with partial ambiguity of
Unsizetraits during selection. However, I pessimistically implemented selection in the new trait solver to just bail out with ambiguity if it was a built-in impl:rust/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs
Line 126 in 9227ff2
This implements a proper "rematch" procedure for dealing with built-in
Unsizegoals, so that even if the goal is ambiguous, we are able to get nested obligations which are used in the coercion selection-like loop:rust/compiler/rustc_hir_typeck/src/coercion.rs
Line 702 in 9227ff2
Second commit just moves a
resolve_vars_if_possiblecall to fix a bug where we weren't detecting a trait upcasting to occur.r? @lcnr