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eb378d2015
Improve type mismatch w/ function signatures This PR makes use of `note: expected/found` (instead of labeling types in labels) in type mismatch with function signatures. Pros: it's easier to compare the signatures, cons: the error is a little more verbose now. This is especially nice when - The signatures differ in a small subset of parameters (same parameters are elided) - The difference is in details, for example `isize` vs `usize` (there is a better chance that the types align) Also this PR fixes the inconsistency in variable names in the edited code (`expected` and `found`). A zulip thread from which this pr started: [[link]](https://rust-lang.zulipchat.com/#narrow/stream/147480-t-compiler.2Fwg-diagnostics/topic/Type.20error.20regression.3F.2E.2E.2E/near/289756602). An example diagnostic: <table> <tr> <th>this pr</th> <th>nightly</th> </tr> <tr> <td> ```text error[E0631]: type mismatch in function arguments --> ./t.rs:4:12 | 4 | expect(&f); | ------ ^^ expected due to this | | | required by a bound introduced by this call ... 10 | fn f(_: isize, _: u8, _: Vec<u32>) {} | ---------------------------------- found signature defined here | = note: expected function signature `fn(usize, _, Vec<u64>) -> _` found function signature `fn(isize, _, Vec<u32>) -> _` note: required because of the requirements on the impl of `Trait` for `fn(isize, u8, Vec<u32>) {f}` --> ./t.rs:8:9 | 8 | impl<F> Trait for F where F: Fn(usize, u8, Vec<u64>) -> u8 {} | ^^^^^ ^ = note: required for the cast from `fn(isize, u8, Vec<u32>) {f}` to the object type `dyn Trait` ``` </td> <td> ```text error[E0631]: type mismatch in function arguments --> ./t.rs:4:12 | 4 | expect(&f); | ------ ^^ expected signature of `fn(usize, u8, Vec<u64>) -> _` | | | required by a bound introduced by this call ... 10 | fn f(_: isize, _: u8, _: Vec<u32>) {} | ---------------------------------- found signature of `fn(isize, u8, Vec<u32>) -> _` | note: required because of the requirements on the impl of `Trait` for `fn(isize, u8, Vec<u32>) {f}` --> ./t.rs:8:9 | 8 | impl<F> Trait for F where F: Fn(usize, u8, Vec<u64>) -> u8 {} | ^^^^^ ^ = note: required for the cast to the object type `dyn Trait` ``` </td> </tr> </table> <details><summary>code</summary> <p> ```rust fn main() { fn expect(_: &dyn Trait) {} expect(&f); } trait Trait {} impl<F> Trait for F where F: Fn(usize, u8, Vec<u64>) -> u8 {} fn f(_: isize, _: u8, _: Vec<u32>) {} ``` </p> </details> r? `@compiler-errors` |
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