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New "type annotations needed" error in Rust nightly-2025-06-24

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

I-libs-nominatedNominated for discussion during a libs team meeting.Nominated for discussion during a libs team meeting.

P-highHigh priorityHigh priority

regression-from-stable-to-nightlyPerformance or correctness regression from stable to nightly.Performance or correctness regression from stable to nightly.

T-libs-apiRelevant to the library API team, which will review and decide on the PR/issue.Relevant to the library API team, which will review and decide on the PR/issue.

Status: Open.

#143164 In rust-lang/rust;

· sunfishcode opened on Jun 28, 2025

3 comments

Const generic type inference works when it should not

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

F-generic_const_exprs`#![feature(generic_const_exprs)]``#![feature(generic_const_exprs)]`

P-lowLow priorityLow priority

requires-incomplete-featuresThis issue requires the use of incomplete features.This issue requires the use of incomplete features.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#142378 In rust-lang/rust;

· nazar-pc opened on Jun 11, 2025

3 comments

type annotations needed for if let Some(whatever) = todo!() { not very helpful

A-diagnosticsArea: Messages for errors, warnings, and lintsArea: Messages for errors, warnings, and lints

A-inferenceArea: Type inferenceArea: Type inference

A-patternsRelating to patterns and pattern matchingRelating to patterns and pattern matching

D-lack-of-suggestionDiagnostics: Adding a (structured) suggestion would increase the quality of the diagnostic.Diagnostics: Adding a (structured) suggestion would increase the quality of the diagnostic.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#141742 In rust-lang/rust;

· matthiaskrgr opened on May 29, 2025

4 comments

type inference failure confusing diagnostic let Some(x) = None for [u8]

A-diagnosticsArea: Messages for errors, warnings, and lintsArea: Messages for errors, warnings, and lints

A-inferenceArea: Type inferenceArea: Type inference

D-confusingDiagnostics: Confusing error or lint that should be reworked.Diagnostics: Confusing error or lint that should be reworked.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#141336 In rust-lang/rust;

· midnightveil opened on May 21, 2025

8 comments

Unexpected type inference failure when comparing Vec::<T>::new() to an empty array []

A-inferenceArea: Type inferenceArea: Type inference

C-discussionCategory: Discussion or questions that doesn't represent real issues.Category: Discussion or questions that doesn't represent real issues.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#141329 In rust-lang/rust;

· 623637646 opened on May 21, 2025

1 comment

Diverging expression not detected inside a while condition

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

T-langRelevant to the language teamRelevant to the language team

T-typesRelevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.

Status: Open.

#141274 In rust-lang/rust;

· theemathas opened on May 20, 2025

2 comments

Making trait method async causes inference failure (E0790)

A-async-awaitArea: Async & AwaitArea: Async & Await

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

T-typesRelevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.

Status: Open.

#140987 In rust-lang/rust;

· benschulz opened on May 14, 2025

Bug: chained where T: trait multiple applicable items

A-inferenceArea: Type inferenceArea: Type inference

A-method-lookupArea: method lookup (typeck, post `rustc_resolve`, not to be confused with `A-resolve`)Area: method lookup (typeck, post `rustc_resolve`, not to be confused with `A-resolve`)

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#140892 In rust-lang/rust;

· RoDmitry opened on May 10, 2025

Type annotations needed for closure with associated type

A-closuresArea: Closures (`|…| { … }`)Area: Closures (`|…| { … }`)

A-inferenceArea: Type inferenceArea: Type inference

C-enhancementCategory: An issue proposing an enhancement or a PR with one.Category: An issue proposing an enhancement or a PR with one.

T-typesRelevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.

Status: Open.

#140603 In rust-lang/rust;

· camsteffen opened on May 3, 2025

1 comment

Unexpected "cannot infer type"

A-diagnosticsArea: Messages for errors, warnings, and lintsArea: Messages for errors, warnings, and lints

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#140262 In rust-lang/rust;

· Spxg opened on Apr 24, 2025

3 comments



Strange inference failure with Arc::new_cyclic

A-inferenceArea: Type inferenceArea: Type inference

C-discussionCategory: Discussion or questions that doesn't represent real issues.Category: Discussion or questions that doesn't represent real issues.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#139736 In rust-lang/rust;

· Sky9x opened on Apr 13, 2025

3 comments

ICE: stack overflow with -Ztyping-mode-borrowck in inference

A-impl-traitArea: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch.Area: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch.

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

I-crashIssue: The compiler crashes (SIGSEGV, SIGABRT, etc). Use I-ICE instead when the compiler panics.Issue: The compiler crashes (SIGSEGV, SIGABRT, etc). Use I-ICE instead when the compiler panics.

requires-nightlyThis issue requires a nightly compiler in some way.This issue requires a nightly compiler in some way.

S-has-mcveStatus: A Minimal Complete and Verifiable Example has been found for this issueStatus: A Minimal Complete and Verifiable Example has been found for this issue

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#139446 In rust-lang/rust;

· matthiaskrgr opened on Apr 6, 2025

1 comment

failed type inference when indexing vec-of-vec in closure

A-diagnosticsArea: Messages for errors, warnings, and lintsArea: Messages for errors, warnings, and lints

A-inferenceArea: Type inferenceArea: Type inference

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#139334 In rust-lang/rust;

· lolbinarycat opened on Apr 3, 2025

3 comments

error[E0282]: type annotations needed but should be inferred automatically

A-inferenceArea: Type inferenceArea: Type inference

C-enhancementCategory: An issue proposing an enhancement or a PR with one.Category: An issue proposing an enhancement or a PR with one.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

T-typesRelevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.

Status: Open.

#139168 In rust-lang/rust;

· Zercerium opened on Mar 31, 2025

3 comments

Can't infer both sides of a Result when using ?

A-inferenceArea: Type inferenceArea: Type inference

C-discussionCategory: Discussion or questions that doesn't represent real issues.Category: Discussion or questions that doesn't represent real issues.

Status: Open.

#138579 In rust-lang/rust;

· richo opened on Mar 16, 2025

5 comments

impl Fn(T) argument type is not infered from return type

A-impl-traitArea: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch.Area: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch.

A-inferenceArea: Type inferenceArea: Type inference

C-discussionCategory: Discussion or questions that doesn't represent real issues.Category: Discussion or questions that doesn't represent real issues.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#138530 In rust-lang/rust;

· LHolten opened on Mar 15, 2025

2 comments

Type inference fails when using associated type in traits

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#138057 In rust-lang/rust;

· StealthyKamereon opened on Mar 5, 2025

1 comment

Incomplete inference guidance due to Sized param-env clause causes method selection failure

A-inferenceArea: Type inferenceArea: Type inference

A-trait-systemArea: Trait systemArea: Trait system

C-bugCategory: This is a bug.Category: This is a bug.

fixed-by-next-solverFixed by the next-generation trait solver, `-Znext-solver`.Fixed by the next-generation trait solver, `-Znext-solver`.

T-typesRelevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.

Status: Open.

#137812 In rust-lang/rust;

· compiler-errors opened on Feb 28, 2025

1 comment

pow inference is not great

A-inferenceArea: Type inferenceArea: Type inference

C-discussionCategory: Discussion or questions that doesn't represent real issues.Category: Discussion or questions that doesn't represent real issues.

T-typesRelevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.

Status: Open.

#137644 In rust-lang/rust;

· oriongonza opened on Feb 25, 2025

3 comments

Rust fails to coerce to a fn pointer when passing an array as an argument to a generic function.

A-coercionsArea: implicit and explicit `expr as Type` coercionsArea: implicit and explicit `expr as Type` coercions

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

T-typesRelevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.

Status: Open.

#136420 In rust-lang/rust;

· theemathas opened on Feb 2, 2025

1

2 comments



Result type inference breaks in 2024 edition, while working correctly in 2021 edition

A-coercionsArea: implicit and explicit `expr as Type` coercionsArea: implicit and explicit `expr as Type` coercions

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

F-never_type`#![feature(never_type)]``#![feature(never_type)]`

T-typesRelevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.

Status: Open.

#135864 In rust-lang/rust;

· nazar-pc opened on Jan 22, 2025

9 comments

Type inference issues with well specified trait function call

A-diagnosticsArea: Messages for errors, warnings, and lintsArea: Messages for errors, warnings, and lints

A-inferenceArea: Type inferenceArea: Type inference

A-suggestion-diagnosticsArea: Suggestions generated by the compiler applied by `cargo fix`Area: Suggestions generated by the compiler applied by `cargo fix`

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#135698 In rust-lang/rust;

· weiznich opened on Jan 18, 2025

2 comments

Please lint on a.eq(b.into()) if a.eq(b) would work

A-inferenceArea: Type inferenceArea: Type inference

A-lintsArea: Lints (warnings about flaws in source code) such as unused_mut.Area: Lints (warnings about flaws in source code) such as unused_mut.

C-feature-requestCategory: A feature request, i.e: not implemented / a PR.Category: A feature request, i.e: not implemented / a PR.

T-langRelevant to the language teamRelevant to the language team

Status: Open.

Feature Request

#135201 In rust-lang/rust;

· joshtriplett opened on Jan 7, 2025

3 comments

Unexpected behavior with type inference

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#134854 In rust-lang/rust;

· zadlg opened on Dec 28, 2024

Hidden type of "discarded" and thus unconstrained RPIT(IT) opaque types gets inferred to be the unit type ()

A-impl-traitArea: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch.Area: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch.

A-inferenceArea: Type inferenceArea: Type inference

C-bugCategory: This is a bug.Category: This is a bug.

fixed-by-next-solverFixed by the next-generation trait solver, `-Znext-solver`.Fixed by the next-generation trait solver, `-Znext-solver`.

P-lowLow priorityLow priority

T-typesRelevant to the types team, which will review and decide on the PR/issue.Relevant to the types team, which will review and decide on the PR/issue.

Status: Open.

#134311 In rust-lang/rust;

· fmease opened on Dec 14, 2024

1 comment