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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>
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