Improve E0308 error message for impl Trait return mismatches#155546
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rust-bors[bot] merged 1 commit intorust-lang:mainfrom Apr 22, 2026
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Improve E0308 error message for impl Trait return mismatches#155546rust-bors[bot] merged 1 commit intorust-lang:mainfrom
impl Trait return mismatches#155546rust-bors[bot] merged 1 commit intorust-lang:mainfrom
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When a function returns `impl Trait`, all branches must return the same
concrete type. Previously, the compiler showed:
expected `First` because of return type
This was misleading, as it suggested the return type was `First`, rather
than any single type implementing the trait.
Update the diagnostic to:
expected a single type implementing `Value` because of return type
Also highlight the first return expression to make it clearer why
subsequent returns do not match.
Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>
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r? @chenyukang rustbot has assigned @chenyukang. Use Why was this reviewer chosen?The reviewer was selected based on:
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Fix: #155366 |
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cc: @DanielEScherzer |
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Apr 20, 2026
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@bors r+ |
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…uwer Rollup of 5 pull requests Successful merges: - #155546 (Improve E0308 error message for `impl Trait` return mismatches) - #152834 (Fix incorrect `let` to `const` suggestion for pattern bindings) - #155425 (Remove duplicated `Flags` methods.) - #155547 (Use per-parent disambiguators everywhere) - #155590 (Remove AttributeLintKind variants - part 5)
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Rollup merge of #155546 - Unique-Usman:ua/impl_traits, r=estebank Improve E0308 error message for `impl Trait` return mismatches When a function returns `impl Trait`, all branches must return the same concrete type. Previously, the compiler showed: expected `First` because of return type This was misleading, as it suggested the return type was `First`, rather than any single type implementing the trait. Update the diagnostic to: expected a single type implementing `Value` because of return type Also highlight the first return expression to make it clearer why subsequent returns do not match.
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nit: @Unique-Usman The issue is automatically closed only when this phrase is in the PR description, not comment. |
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noted. |
JonathanBrouwer
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Apr 26, 2026
Add boxing suggestions for `impl Trait` return type mismatches A sort of a follow up pr to this -> rust-lang#155546
JonathanBrouwer
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Add boxing suggestions for `impl Trait` return type mismatches A sort of a follow up pr to this -> rust-lang#155546
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Add boxing suggestions for `impl Trait` return type mismatches A sort of a follow up pr to this -> rust-lang#155546
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When a function returns
impl Trait, all branches must return the same concrete type. Previously, the compiler showed:This was misleading, as it suggested the return type was
First, rather than any single type implementing the trait.Update the diagnostic to:
Also highlight the first return expression to make it clearer why subsequent returns do not match.