When single impl can satisfy inference error, suggest type#153727
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estebank wants to merge 1 commit intorust-lang:mainfrom
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When single impl can satisfy inference error, suggest type#153727estebank wants to merge 1 commit intorust-lang:mainfrom
estebank wants to merge 1 commit intorust-lang:mainfrom
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Some changes occurred in need_type_info.rs cc @lcnr |
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r? @JohnTitor rustbot has assigned @JohnTitor. Use Why was this reviewer chosen?The reviewer was selected based on:
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estebank
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Mar 11, 2026
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| let mut specific_candidates = candidates.clone(); | ||
| specific_candidates.retain(|(tr, _)| { | ||
| tr.with_replaced_self_ty(self.tcx, trait_pred.skip_binder().self_ty()) | ||
| == trait_pred.skip_binder().trait_ref | ||
| }); | ||
| if !specific_candidates.is_empty() { | ||
| // We have found a subset of impls that fully satisfy the expected trait, only | ||
| // mention those types. | ||
| candidates = specific_candidates; | ||
| } |
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This gives us the
help: the trait `Sum` is implemented for `i32`
--> library/core/src/iter/traits/accum.rs:48:9
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48 | impl Sum for $a {
| ^^^^^^^^^^^^^^^
...
204 | integer_sum_product! { i8 i16 i32 i64 i128 isize u8 u16 u32 u64 u128 usize }
| ---------------------------------------------------------------------------- in this macro invocation
instead of
= help: the following types implement trait `Sum<A>`:
`Duration` implements `Sum<&'a Duration>`
`Duration` implements `Sum`
`Option<T>` implements `Sum<Option<U>>`
`Result<T, E>` implements `Sum<Result<U, E>>`
`Saturating<u128>` implements `Sum<&'a Saturating<u128>>`
`Saturating<u128>` implements `Sum`
`Saturating<u16>` implements `Sum<&'a Saturating<u16>>`
`Saturating<u16>` implements `Sum`
and 88 others
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When encountering an inference error where a return type must be known, like when calling `Iterator::sum::<T>()` without specifying `T`, look for all `T` that would satisfy `Sum<S>`. If only one, suggest it. ``` error[E0283]: type annotations needed --> $DIR/cannot-infer-iterator-sum-return-type.rs:4:9 | LL | let sum = v | ^^^ ... LL | .sum(); // `sum::<T>` needs `T` to be specified | --- type must be known at this point | = note: cannot satisfy `_: Sum<i32>` help: the trait `Sum` is implemented for `i32` --> $SRC_DIR/core/src/iter/traits/accum.rs:LL:COL ::: $SRC_DIR/core/src/iter/traits/accum.rs:LL:COL | = note: in this macro invocation note: required by a bound in `std::iter::Iterator::sum` --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL = note: this error originates in the macro `integer_sum_product` (in Nightly builds, run with -Z macro-backtrace for more info) help: consider giving `sum` an explicit type, where the type for type parameter `S` is specified | LL | let sum: i32 = v | +++++ ```
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When encountering an inference error where a return type must be known, like when calling
Iterator::sum::<T>()without specifyingT, look for allTthat would satisfySum<S>. If only one, suggest it.Fix #100802.