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Mismatched closure arguments are no longer expanded in rustc 1.64 and later #100690
Description
Sorry, this is not necessarily the smallest possible example. Please let me know if this is unhelpful and I'll come up with something more concise.
Given the following code: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=8a1f669598035e38e7e141eb799d6738
use std::io;
fn real_dispatch<T, F>(f: F) -> Result<(), io::Error>
where
F: FnOnce(&mut UIView<T>) -> Result<(), io::Error> + Send + 'static,
{
todo!()
}
#[derive(Debug)]
struct UIView<'a, T: 'a> {
_phantom: std::marker::PhantomData<&'a mut T>,
}
trait Handle<'a, T: 'a, V, R> {
fn dispatch<F>(&self, f: F) -> Result<(), io::Error>
where
F: FnOnce(&mut V) -> R + Send + 'static;
}
#[derive(Debug, Clone)]
struct TUIHandle<T> {
_phantom: std::marker::PhantomData<T>,
}
impl<'a, T: 'a> Handle<'a, T, UIView<'a, T>, Result<(), io::Error>> for TUIHandle<T> {
fn dispatch<F>(&self, f: F) -> Result<(), io::Error>
where
F: FnOnce(&mut UIView<'a, T>) -> Result<(), io::Error> + Send + 'static,
{
real_dispatch(f)
}
}The output in current stable (1.63.0) is:
(Please note the "expected closure with ... found closure with ..." hint.)
error[E0277]: expected a `FnOnce<(&mut UIView<'_, T>,)>` closure, found `F`
--> src/lib.rs:31:23
|
31 | real_dispatch(f)
| ------------- ^ expected an `FnOnce<(&mut UIView<'_, T>,)>` closure, found `F`
| |
| required by a bound introduced by this call
|
= note: expected a closure with arguments `(&mut UIView<'a, T>,)`
found a closure with arguments `(&mut UIView<'_, T>,)`
note: required by a bound in `real_dispatch`
--> src/lib.rs:5:8
|
3 | fn real_dispatch<T, F>(f: F) -> Result<(), io::Error>
| ------------- required by a bound in this
4 | where
5 | F: FnOnce(&mut UIView<T>) -> Result<(), io::Error> + Send + 'static,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `real_dispatch`
For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` due to previous error
From 1.64 onwards, the expected/found hint is omitted:
error[E0277]: expected a `FnOnce<(&mut UIView<'_, T>,)>` closure, found `F`
--> src/lib.rs:31:23
|
31 | real_dispatch(f)
| ------------- ^ expected an `FnOnce<(&mut UIView<'_, T>,)>` closure, found `F`
| |
| required by a bound introduced by this call
|
note: required by a bound in `real_dispatch`
--> src/lib.rs:5:8
|
3 | fn real_dispatch<T, F>(f: F) -> Result<(), io::Error>
| ------------- required by a bound in this
4 | where
5 | F: FnOnce(&mut UIView<T>) -> Result<(), io::Error> + Send + 'static,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `real_dispatch`
For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` due to previous error
To me the 1.63 behaviour is preferable to that from 1.64+ as it can often be non-obvious where the differences lie.
Activity
Noratrieb commentedon Aug 17, 2022
searched nightlies: from nightly-2022-06-01 to nightly-2022-08-11
regressed nightly: nightly-2022-07-23
searched commit range: 62b272d...848090d
regressed commit: e7a9c11
bisected with cargo-bisect-rustc v0.6.4
Host triple: x86_64-unknown-linux-gnu
Reproduce with:
Noratrieb commentedon Aug 17, 2022
Looks like it was caused by #99539, which is pretty big diagnostics PR in that rollup. cc @compiler-errors
compiler-errors commentedon Aug 17, 2022
Of course I caused it.
steffahn commentedon Aug 17, 2022
@rustbot label -E-needs-bisection
apiraino commentedon Aug 18, 2022
WG-prioritization assigning priority (Zulip discussion).
@rustbot label -I-prioritize +P-medium
Rollup merge of rust-lang#100691 - compiler-errors:issue-100690, r=es…
Rollup merge of rust-lang#100691 - compiler-errors:issue-100690, r=es…