Misleading compiler suggestion: Swapp the equality in rustlib due to mismatched types in user code #139050
Description
Code
use std::fmt::Debug; pub fn foo<I: Iterator>(mut iter: I, value: &I::Item) where Item: Eq + Debug, { debug_assert_eq!(iter.next(), Some(value)); } fn main() {}Current output
error[E0412]: cannot find type `Item` in this scope --> .\test.rs:5:5 | 5 | Item: Eq + Debug, | ^^^^ not found in this scope error[E0308]: mismatched types --> .\test.rs:7:35 | 7 | debug_assert_eq!(iter.next(), Some(value)); | ^^^^^^^^^^^ expected `Option<<I as Iterator>::Item>`, found `Option<&<I as Iterator>::Item>` | = note: expected enum `Option<_>` found enum `Option<&_>` = note: `Option<&<I as Iterator>::Item>` implements `PartialEq<Option<<I as Iterator>::Item>>` help: consider swapping the equality --> C:\Users\jjl98\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib/rustlib/src/rust\library\core\src\macros\mod.rs:46:22 | 46| if !(*right_val == *left_val) { | ~~~~~~~~~~ ~~~~~~~~~ error: aborting due to 2 previous errors Some errors have detailed explanations: E0308, E0412. For more information about an error, try `rustc --explain E0308`.Desired output
Rationale and extra context
I'm not entirely sure what the compiler's output should be, but it is inappropriate for the compiler to suggest modifying rustlib when the issue lies in the user code. This suggestion is clearly flawed.
Other cases
Rust Version
rustc 1.85.1 (4eb161250 2025-03-15) binary: rustc commit-hash: 4eb161250e340c8f48f66e2b929ef4a5bed7c181 commit-date: 2025-03-15 host: x86_64-pc-windows-msvc release: 1.85.1 LLVM version: 19.1.7Anything else?
No response
Metadata
Metadata
Assignees
Labels
Area: Messages for errors, warnings, and lintsArea: Trait systemDiagnostics: A structured suggestion resulting in incorrect code.Call for participation: This issue needs bisection: https://github.com/rust-lang/cargo-bisect-rustcRelevant to the compiler team, which will review and decide on the PR/issue.