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Diagnostics incorrectly states that async closure implements <code>Fn</code>.

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

A-async-closures`async || {}``async || {}`

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

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

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.

#148391 In rust-lang/rust;

· theemathas opened on Nov 2, 2025

unnecessary closure constraint propagation

A-borrow-checkerArea: The borrow checkerArea: The borrow checker

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

A-higher-rankedArea: Higher-ranked things (e.g., lifetimes, types, trait bounds aka HRTBs)Area: Higher-ranked things (e.g., lifetimes, types, trait bounds aka HRTBs)

A-lifetimesArea: Lifetimes / regionsArea: Lifetimes / regions

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

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.

#148289 In rust-lang/rust;

· lcnr opened on Oct 30, 2025

Should <code>const FnMut</code> require <code>const FnOnce</code>?

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

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

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

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

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.

#148251 In rust-lang/rust;

· theemathas opened on Oct 29, 2025

Closure formatting in diagnostics can be a bit verbose

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

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

A-prettyArea: Pretty printing (including `-Z unpretty`)Area: Pretty printing (including `-Z unpretty`)

D-verboseDiagnostics: Too much output caused by a single piece of incorrect code.Diagnostics: Too much output caused by a single piece of incorrect code.

P-lowLow priorityLow priority

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.

#148236 In rust-lang/rust;

· jieyouxu opened on Oct 29, 2025

<code>&amp;mut impl Fn()</code> does not implement <code>Fn()</code>

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

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

needs-triageThis issue may need triage. Remove it if it has been sufficiently triaged.This issue may need triage. Remove it if it has been sufficiently triaged.

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.

#147931 In rust-lang/rust;

· theemathas opened on Oct 21, 2025

Odd lifetime error with closures and HRTBs

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

A-higher-rankedArea: Higher-ranked things (e.g., lifetimes, types, trait bounds aka HRTBs)Area: Higher-ranked things (e.g., lifetimes, types, trait bounds aka HRTBs)

A-implied-boundsArea: Implied bounds / inferred outlives-boundsArea: Implied bounds / inferred outlives-bounds

A-lifetimesArea: Lifetimes / regionsArea: Lifetimes / regions

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.

#147618 In rust-lang/rust;

· comex opened on Oct 12, 2025

Incoherent (?) Lifetime HRTB on associated type results in unsoundness in stable, safe code

A-associated-itemsArea: Associated items (types, constants & functions)Area: Associated items (types, constants & functions)

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

A-type-systemArea: Type systemArea: Type system

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

I-unsoundIssue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/SoundnessIssue: A soundness hole (worst kind of bug), see: https://en.wikipedia.org/wiki/Soundness

P-highHigh priorityHigh priority

regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.Performance or correctness regression from one stable version to another.

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.

#141713 In rust-lang/rust;

· maxdexh opened on May 29, 2025

LLVM optimization often (always?) results of loss of closure upvar debug info

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

A-debuginfoArea: Debugging information in compiled programs (DWARF, PDB, etc.)Area: Debugging information in compiled programs (DWARF, PDB, etc.)

A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.

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

WG-llvmWorking group: LLVM backend code generationWorking group: LLVM backend code generation

Status: Open.

#141712 In rust-lang/rust;

· khuey opened on May 29, 2025

<code>unused_assignment</code> triggered by closure even though value is used

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

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

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.

D-imprecise-spansDiagnostics: spans don't point to exactly the erroneous codeDiagnostics: spans don't point to exactly the erroneous code

L-unused_assignmentsLint: unused_assignmentsLint: unused_assignments

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.

#141615 In rust-lang/rust;

· BennoLossin opened on May 26, 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

LUB coercions works for a function but fails for a closure

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

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

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

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

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.

#132643 In rust-lang/rust;

· pazmank opened on Nov 5, 2024

Closure breaks function with higher-ranked trait bound

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

A-higher-rankedArea: Higher-ranked things (e.g., lifetimes, types, trait bounds aka HRTBs)Area: Higher-ranked things (e.g., lifetimes, types, trait bounds aka HRTBs)

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.

#131677 In rust-lang/rust;

· drewtato opened on Oct 14, 2024