Esteban Küber 49bb371ca7 When single impl can satisfy inference error, suggest type ...

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
   |            +++++
```

2026-03-18 18:16:47 +00:00

..

auxiliary

Arbitrary self types v2: pointers feature gate.

2024-08-27 17:32:35 +00:00

need_type_info

Tweak wording of failed predicate in inference error

2026-03-16 17:58:49 +00:00

ambiguous_type_parameter.rs

…

ambiguous_type_parameter.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

ambiguous-numeric-in-closure-ref.fixed

Fix suggestions for nested refs and muts

2025-10-11 21:17:17 +09:00

ambiguous-numeric-in-closure-ref.rs

Fix suggestions for nested refs and muts

2025-10-11 21:17:17 +09:00

ambiguous-numeric-in-closure-ref.stderr

Fix suggestions for nested refs and muts

2025-10-11 21:17:17 +09:00

array-len-mismatch.rs

…

array-len-mismatch.stderr

Make some suggestions verbose

2026-03-14 20:13:43 +00:00

auto-instantiate.rs

tests: adjust tests/ui/auto-instantiate.rs

2025-04-19 18:42:24 +08:00

bitwise-integer-inference-68951.rs

Add test batch 4

2025-10-11 21:59:51 -04:00

cannot-infer-async.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

cannot-infer-async.stderr

Show number in error message even for one error

2023-11-24 19:15:52 +01:00

cannot-infer-closure-circular.rs

Use fn ptr signature instead of {closure@..} in infer error

2024-04-10 00:41:27 +00:00

cannot-infer-closure-circular.stderr

In "specify type" suggestion, skip type params that are already known

2025-02-03 19:51:20 +00:00

cannot-infer-closure.rs

…

cannot-infer-closure.stderr

Show number in error message even for one error

2023-11-24 19:15:52 +01:00

cannot-infer-iterator-sum-return-type.fixed

When single impl can satisfy inference error, suggest type

2026-03-18 18:16:47 +00:00

cannot-infer-iterator-sum-return-type.rs

When single impl can satisfy inference error, suggest type

2026-03-18 18:16:47 +00:00

cannot-infer-iterator-sum-return-type.stderr

When single impl can satisfy inference error, suggest type

2026-03-18 18:16:47 +00:00

cannot-infer-partial-try-return.rs

…

cannot-infer-partial-try-return.stderr

Show number in error message even for one error

2023-11-24 19:15:52 +01:00

char-as-str-multi.rs

…

char-as-str-multi.stderr

…

char-as-str-single.fixed

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

char-as-str-single.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

char-as-str-single.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

collection-type-copy-behavior-12909.rs

Rehome tests/ui/issues/ tests [2/?]

2025-08-02 15:29:16 -04:00

deref-suggestion.rs

…

deref-suggestion.stderr

Make Diag::multipart_suggestions always verbose

2025-07-10 17:23:29 +00:00

dont-collect-stmts-from-parent-body.rs

Don't proceed into parent bodies when collecting stmts for possible return suggestion

2024-04-16 15:56:48 -04:00

dont-collect-stmts-from-parent-body.stderr

Don't proceed into parent bodies when collecting stmts for possible return suggestion

2024-04-16 15:56:48 -04:00

erase-type-params-in-label.rs

…

erase-type-params-in-label.stderr

Tweak wording of failed predicate in inference error

2026-03-16 17:58:49 +00:00

fnonce-closure-call.rs

comments

2025-07-25 20:38:54 +05:00

generic-type-inference-10436.rs

comments

2025-07-25 20:38:54 +05:00

hint-closure-signature-119266.rs

compiletest: Improve diagnostics for line annotation mismatches

2025-06-23 21:30:56 +03:00

hint-closure-signature-119266.stderr

Print note with closure signature on type mismatch

2024-04-20 15:48:27 +02:00

ice-cannot-relate-region-109178.rs

Split part of adt_const_params into unsized_const_params

2024-07-17 11:01:29 +01:00

ice-cannot-relate-region-109178.stderr

add test for ice "cannot relate region: LUB(ReErased, ReError)"

2024-03-21 22:02:32 +01:00

ice-ifer-var-leaked-out-of-rollback-122098.rs

add test for https://github.com/rust-lang/rust/issues/122098 ICE: index out of bounds, snapshot_vec.rs

2024-03-21 20:57:54 +01:00

ice-ifer-var-leaked-out-of-rollback-122098.stderr

Make missing lifetime suggestion verbose

2025-06-24 18:59:42 +00:00

infer-binary-operand-behind-reference.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

infer-fn-tail-expr.rs

tests: remove //@ pretty-expanded usages

2024-11-26 02:50:48 +08:00

inference_unstable_featured.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

inference_unstable_featured.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

inference_unstable_forced.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

inference_unstable_forced.stderr

use backticks instead of single quotes when reporting "use of unstable library feature"

2024-11-03 13:55:52 -08:00

inference_unstable.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

inference_unstable.stderr

Remove TyCtxt::node_span_lint usage from rustc_hir_typeck

2026-03-05 23:53:54 +01:00

inference-thread-loop-closure.rs

cleaned up some tests

2025-12-13 00:54:20 +09:00

inference-variable-behind-raw-pointer.rs

Gate 2015 UI tests

2025-11-27 11:19:00 -05:00

inference-variable-behind-raw-pointer.stderr

bless the tests

2025-12-10 15:15:56 +01:00

issue-3743.rs

Move tests

2024-03-03 16:30:48 -03:00

issue-12028.rs

Move tests

2024-02-13 18:08:25 -03:00

issue-12028.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

issue-28935.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

issue-36053.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

issue-70082.rs

…

issue-70082.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

issue-70703.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

issue-71309.rs

…

issue-71309.stderr

Show number in error message even for one error

2023-11-24 19:15:52 +01:00

issue-71584.rs

Enable more tests on Windows

2025-02-03 10:39:32 -05:00

issue-71584.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

issue-71732.rs

…

issue-71732.stderr

Update UI tests for addition of HashMap allocator

2025-12-29 17:41:49 -08:00

issue-72616.rs

std: simplify host lookup

2025-09-19 11:30:27 +02:00

issue-72616.stderr

Remove named lifetimes in some PartialOrd & PartialEq impls

2026-02-14 00:13:46 +03:00

issue-72690.rs

…

issue-72690.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

issue-80409.compat.stderr

Check closure args and returns are WF

2024-04-25 10:03:17 -04:00

issue-80409.no-compat.stderr

Check closure args and returns are WF

2024-04-25 10:03:17 -04:00

issue-80409.rs

Check closure args and returns are WF

2024-04-25 10:03:17 -04:00

issue-80816.rs

…

issue-80816.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

issue-81522.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

issue-83606.rs

Partially implement ConstArgHasType

2024-05-29 17:06:54 +01:00

issue-83606.stderr

In "specify type" suggestion, skip type params that are already known

2025-02-03 19:51:20 +00:00

issue-86094-suggest-add-return-to-coerce-ret-ty.rs

Suggest adding return if the type of unused semi return value can coerce to the fn return type

2023-10-15 22:57:03 +08:00

issue-86094-suggest-add-return-to-coerce-ret-ty.stderr

Remove MaybeForgetReturn suggestion

2025-02-22 00:04:26 +00:00

issue-86162-1.rs

…

issue-86162-1.stderr

Tweak wording of failed predicate in inference error

2026-03-16 17:58:49 +00:00

issue-86162-2.rs

…

issue-86162-2.stderr

Tweak wording of failed predicate in inference error

2026-03-16 17:58:49 +00:00

issue-103587.rs

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issue-103587.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

issue-104649.rs

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issue-104649.stderr

In "specify type" suggestion, skip type params that are already known

2025-02-03 19:51:20 +00:00

issue-107090.rs

make type_flags(ReError) & HAS_ERROR

2024-03-20 17:29:58 +00:00

issue-107090.stderr

Make missing lifetime suggestion verbose

2025-06-24 18:59:42 +00:00

issue-113354.fixed

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

issue-113354.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

issue-113354.stderr

Show number in error message even for one error

2023-11-24 19:15:52 +01:00

iterator-sum-array-15673.rs

remove #![allow(stable_features)] from most tests

2026-02-17 08:45:08 +00:00

lambda-infer-unresolved.rs

Move 100 entries from tests/ui into subdirs

2024-05-20 19:55:59 -07:00

lub-glb-with-unbound-infer-var.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

matcher-lifetime-inference-14919.rs

comments

2025-08-05 19:34:46 +05:00

multiple-impl-apply.rs

Reorder fullfillment errors to keep more interesting ones first

2023-10-04 02:04:14 +00:00

multiple-impl-apply.stderr

Show number in error message even for one error

2023-11-24 19:15:52 +01:00

newlambdas-ret-infer2.rs

tests: remove //@ pretty-expanded usages

2024-11-26 02:50:48 +08:00

newlambdas-ret-infer.rs

tests: remove //@ pretty-expanded usages

2024-11-26 02:50:48 +08:00

note-and-explain-ReVar-124973.rs

c_variadic: Add future-incompatibility warning for ... arguments without a pattern outside of extern blocks

2025-11-10 14:33:56 +01:00

note-and-explain-ReVar-124973.stderr

Use return type Span on async fns instead of whole fn def Span

2025-12-09 16:46:33 +00:00

order-dependent-cast-inference.rs

Move 100 entries from tests/ui into subdirs

2024-05-20 19:55:59 -07:00

order-dependent-cast-inference.stderr

Move 100 entries from tests/ui into subdirs

2024-05-20 19:55:59 -07:00

question-mark-type-infer.rs

Provide better suggestions for inference errors on .collect()?

2026-03-15 17:39:06 +00:00

question-mark-type-infer.stderr

Tweak wording of failed predicate in inference error

2026-03-16 17:58:49 +00:00

question-mark-type-inference-in-chain.rs

Tweak wording of failed predicate in inference error

2026-03-16 17:58:49 +00:00

question-mark-type-inference-in-chain.stderr

Tweak wording of failed predicate in inference error

2026-03-16 17:58:49 +00:00

range-type-infer.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

really-long-type-in-let-binding-without-sufficient-type-info.rs

Use tcx.short_string() in more diagnostics

2025-08-07 21:18:00 +00:00

really-long-type-in-let-binding-without-sufficient-type-info.stderr

Use tcx.short_string() in more diagnostics

2025-08-07 21:18:00 +00:00

return-block-type-inference-15965.rs

comments

2025-08-09 16:27:20 +05:00

return-block-type-inference-15965.stderr

support calls on opaque types :<

2025-09-18 12:58:38 +02:00

simple-infer.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

stmts-as-exp-105431.rs

renaming test cases

2024-02-29 08:46:00 +08:00

stmts-as-exp-105431.stderr

renaming test cases

2024-02-29 08:46:00 +08:00

str-as-char-butchered.rs

Don't suggest turning non-char-literal exprs of ty char into string literals

2024-05-28 09:40:02 +02:00

str-as-char-butchered.stderr

Don't suggest turning non-char-literal exprs of ty char into string literals

2024-05-28 09:40:02 +02:00

str-as-char-non-lit.rs

Don't suggest turning non-char-literal exprs of ty char into string literals

2024-05-28 09:40:02 +02:00

str-as-char-non-lit.stderr

Don't suggest turning non-char-literal exprs of ty char into string literals

2024-05-28 09:40:02 +02:00

str-as-char.fixed

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

str-as-char.rs

[AUTO-GENERATED] Migrate ui tests from // to //@ directives

2024-02-16 20:02:50 +00:00

str-as-char.stderr

Show diff suggestion format on verbose replacement

2025-02-10 20:21:39 +00:00

tutorial-suffix-inference-test.rs

compiletest: Make diagnostic kind mandatory on line annotations

2025-04-30 10:44:24 +03:00

tutorial-suffix-inference-test.stderr

compiletest: Make diagnostic kind mandatory on line annotations

2025-04-30 10:44:24 +03:00

type-infer-generalize-ty-var.rs

Ignore tests w/ current/next revisions from compare-mode=next-solver

2024-03-10 21:18:41 -04:00

untyped-primitives.rs

Remove From impls for unstable types that break inference

2024-04-11 18:04:31 -04:00

useless-turbofish-suggestion.rs

Point turbofish inference errors at the uninferred generic arg

2026-03-13 07:29:05 -04:00

useless-turbofish-suggestion.stderr

Point turbofish inference errors at the uninferred generic arg

2026-03-13 07:29:05 -04:00