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Duplicate error messages when RPIT comes from function whose generics don't satisfy bounds #128756
Description
Code
I tried this code:
use std::fmt::Display;
fn foo<T: Display>(x: T) -> impl Display {
x
}
struct Bar; // does'nt impl `Display`
fn main() {
let x = foo(Bar);
println!("{}", x);
}I expected to see this happen:
The error to be reported on the call to foo() only:
error[E0277]: `Bar` doesn't implement `std::fmt::Display`
--> src\lib.rs:10:17
|
10 | let x = foo(Bar);
| --- ^^^ `Bar` cannot be formatted with the default formatter
| |
| required by a bound introduced by this call
|
= help: the trait `std::fmt::Display` is not implemented for `Bar`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
note: required by a bound in `foo`
--> src\lib.rs:3:11
|
3 | fn foo<T: Display>(x: T) -> impl Display {
| ^^^^^^^ required by this bound in `foo`
For more information about this error, try `rustc --explain E0277`.
Instead, this happened:
The error is propagated to the use of the println! macro call, without supposing x to implement Display:
error[E0277]: `Bar` doesn't implement `std::fmt::Display`
--> src\lib.rs:10:17
|
10 | let x = foo(Bar);
| --- ^^^ `Bar` cannot be formatted with the default formatter
| |
| required by a bound introduced by this call
|
= help: the trait `std::fmt::Display` is not implemented for `Bar`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
note: required by a bound in `foo`
--> src\lib.rs:3:11
|
3 | fn foo<T: Display>(x: T) -> impl Display {
| ^^^^^^^ required by this bound in `foo`
error[E0277]: `Bar` doesn't implement `std::fmt::Display`
--> src\lib.rs:10:13
|
10 | let x = foo(Bar);
| ^^^^^^^^ `Bar` cannot be formatted with the default formatter
|
= help: the trait `std::fmt::Display` is not implemented for `Bar`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
note: required by a bound in `foo`
--> src\lib.rs:3:11
|
3 | fn foo<T: Display>(x: T) -> impl Display {
| ^^^^^^^ required by this bound in `foo`
error[E0277]: `Bar` doesn't implement `std::fmt::Display`
--> src\lib.rs:11:15
|
11 | println!("{}", x);
| ^^ `Bar` cannot be formatted with the default formatter
|
= help: the trait `std::fmt::Display` is not implemented for `Bar`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
For more information about this error, try `rustc --explain E0277`.
Version it worked on
It most recently worked on: Rust 1.77
Version with regression
rustc --version --verbose:
rustc 1.80.0 (051478957 2024-07-21)
binary: rustc
commit-hash: 051478957371ee0084a7c0913941d2a8c4757bb9
commit-date: 2024-07-21
host: x86_64-pc-windows-msvc
release: 1.80.0
LLVM version: 18.1.7
Backtrace
Backtrace
<backtrace>
Activity
Baptistemontan commentedon Aug 6, 2024
This problem is quite annoying with macros, as it propagate the error through the whole macro generated code and stop pin-pointing the source of the problem.
Baptistemontan commentedon Aug 6, 2024
The behavior change came with 1.78, I tried 1.78, 1.79, 1.80, 1.81-nightly and 1.82-nightly.
compiler-errors commentedon Aug 6, 2024
This isn't leaking RPITs. This code has the same error:
This just has to do with bad error spans and a lack of error deduplications. The root cause of all 3 of these errors is still the
T: Displaybound.Baptistemontan commentedon Aug 6, 2024
@compiler-errors True, this was a supposition on my part, and I did'nt really know how to name the issue, any suggestion how to rename it ?
[-]RPIT leak concrete type[/-][+]Duplicate error messages when RPIT comes from function whose generics don't satisfy bounds[/+]compiler-errors commentedon Aug 6, 2024
This is purely a diagnostics regression so this doesn't need triaging.
I caused this in #122341. I may spend some time looking into how to deduplicate these error messages.