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<code>-Znext-solver</code> ambiguous opaque types in HIR typeck result in poor errors

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

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

D-terseDiagnostics: An error or lint that doesn't give enough information about the problem at hand.Diagnostics: An error or lint that doesn't give enough information about the problem at hand.

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.

WG-trait-system-refactorThe Rustc Trait System Refactor Initiative (-Znext-solver)The Rustc Trait System Refactor Initiative (-Znext-solver)

Status: Open.

#146231 In rust-lang/rust;

· lcnr opened on Sep 5, 2025

member constraints involving external regions are scuffed

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

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-lifetimesArea: Lifetimes / regionsArea: Lifetimes / regions

A-type-systemArea: Type systemArea: Type system

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.

#146062 In rust-lang/rust;

· lcnr opened on Aug 31, 2025

<code>apply_member_constraints</code> is incomplete

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-member-constraints`#[feature(member_constraints)]``#[feature(member_constraints)]`

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.

#142073 In rust-lang/rust;

· lcnr opened on Jun 5, 2025

member constraints are order-dependent

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-member-constraints`#[feature(member_constraints)]``#[feature(member_constraints)]`

A-NLLArea: Non-lexical lifetimes (NLL)Area: Non-lexical lifetimes (NLL)

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.

#140569 In rust-lang/rust;

· lcnr opened on May 2, 2025

opaque type leakage and RPITIT normalization

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

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

WG-trait-system-refactorThe Rustc Trait System Refactor Initiative (-Znext-solver)The Rustc Trait System Refactor Initiative (-Znext-solver)

Status: Open.

#139788 In rust-lang/rust;

· lcnr opened on Apr 14, 2025

auto trait leakage can be used to leak arbitrary types

A-auto-traitsArea: auto traits (e.g., `auto trait Send {}`)Area: auto traits (e.g., `auto trait Send {}`)

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

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

I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️

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

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.

#134578 In rust-lang/rust;

· lcnr opened on Dec 20, 2024

unchecked region constraints for opaque types in dead code

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

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-mediumMedium priorityMedium priority

S-needs-reproStatus: This issue has no reproduction and needs a reproduction to make progress.Status: This issue has no reproduction and needs a reproduction to make progress.

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.

#112417 In rust-lang/rust;

· lcnr opened on Jun 8, 2023

alias bound candidates for opaques allow cyclic reasoning

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-type-systemArea: Type systemArea: Type system

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

F-type_alias_impl_trait`#[feature(type_alias_impl_trait)]``#[feature(type_alias_impl_trait)]`

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

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

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.

#109387 In rust-lang/rust;

· lcnr opened on Mar 20, 2023