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Rust: Improve type inference for closures and function traits #21170

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Rust: Improve type inference for closures and function traits #21170

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@paldepind paldepind commented Jan 15, 2026

This PR

  • Improves type inference for closures by giving them the type dyn Fn instead of dyn FnOnce. This means that closures can now be passed to places where the trait FnMut and Fn is used.
  • Makes the type mention for FnMut(..) -> .. and Fn(..) -> .. work.

@github-actions github-actions bot added the Rust Pull requests that update Rust code label Jan 15, 2026
github-advanced-security[bot]
github-advanced-security bot found potential problems Jan 15, 2026
View reviewed changes
rust/ql/lib/codeql/rust/frameworks/stdlib/Stdlib.qll
TypeAlias getOutputType() { result = this.(TraitItemNode).getAssocItem("Output") }
}

/** Any of the function traits `FnOnce`, `FnMut`, or `Fn`. */

Check warning

Code scanning / CodeQL

Class QLDoc style Warning

The QLDoc for a class should start with 'A', 'An', or 'The'.
github-advanced-security[bot]
github-advanced-security bot found potential problems Jan 15, 2026
View reviewed changes
rust/tools/builtins/mentions.rs
fn mention_dyn_future<T>(f: &dyn Future<Output = T>) {}

fn mention_dyn_fn_once<F>(f: &dyn FnOnce() -> F) {}
fn mention_dyn_fn_once<F>(f: &dyn Fn() -> F) {}

Check notice

Code scanning / CodeQL

Unused variable Note

Variable 'f' is not used.
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