Auto merge of #44735 - tirr-c:issue-42143, r=arielb1
Friendlier error message for closure argument type mismatch Rebased #42270. Fixes #42143. --- `test.rs`: ```rust fn main() { foo(|_: i32, _: usize| ()); } fn foo<F>(_: F) where F: Fn(&str, usize) {} ``` Before: ``` error[E0281]: type mismatch: `[closure@test.rs:2:9: 2:30]` implements the trait `std::ops::Fn<(i32, usize)>`, but the trait `for<'r> std::ops::Fn<(&'r str, usize)>` is required --> test.rs:2:5 | 2 | foo(|_: i32, _: usize| ()); | ^^^ --------------------- implements `std::ops::Fn<(i32, usize)>` | | | expected &str, found i32 | requires `for<'r> std::ops::Fn<(&'r str, usize)>` | = note: required by `foo` ``` After (early): ``` error[E0631]: type mismatch in closure arguments --> test.rs:2:5 | 2 | foo(|_: i32, _: usize| ()); | ^^^ --------------------- takes arguments of type `i32` and `usize` | | | expected arguments of type `&str` and `usize` | = note: required by `foo` ``` After (current): ``` error[E0631]: type mismatch in closure arguments --> test.rs:2:5 | 2 | foo(|_: i32, _: usize| ()); | ^^^ --------------------- found signature of `fn(i32, usize) -> _` | | | expected signature of `for<'r> fn(&'r str, usize) -> _` | = note: required by `foo` ``` ~~Compiler output has been changed, and a few tests are failing. Help me writing/fixing tests!~~ r? @nikomatsakis
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