Friendlier compiler message for incorrect trait method signatures #28011
Labels
A-diagnostics
Area: Messages for errors, warnings, and lints
Comments
|
I wanted similar behaviour occasionally as well. Looking signatures up in the docs is painful. |
|
related: #24626, which requests the same for missing methods in impls. |
estebank
added a commit
to estebank/rust
that referenced
this issue
Sep 10, 2016
Given file `foo.rs`:
```rust
struct A {}
impl std::fmt::Display for A {
fn fmt() -> () {}
}
```
provide the expected method signature:
```bash
error: main function not found
error[E0186]: method `fmt` has a `&self` declaration in the trait, but not in the impl
--> foo.rs:4:5
|
4 | fn fmt() -> () {}
| ^^^^^^^^^^^^^^^^^ expected `&self` in impl
|
= note: Expected signature: fn fmt(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error>;
= note: Found signature: fn fmt();
error: aborting due to previous error
```
Fixes rust-lang#28011
estebank
added a commit
to estebank/rust
that referenced
this issue
Oct 1, 2016
For a given file `foo.rs`:
```rust
use std::str::FromStr;
struct A {}
trait X<T> {
type Foo;
const BAR: u32 = 128;
fn foo() -> T;
fn bar();
fn bay<
'lifetime, TypeParameterA
>( a : usize,
b: u8 );
}
impl std::fmt::Display for A {
}
impl FromStr for A{}
impl X<usize> for A {
}
```
Provide the following output:
```bash
error: main function not found
error[E0046]: not all trait items implemented, missing: `fmt`
--> foo.rs:18:1
|
18 | impl std::fmt::Display for A {
| ^ missing `fmt` in implementation
|
= note: fn fmt(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error>;
error[E0046]: not all trait items implemented, missing: `Err`, `from_str`
--> foo.rs:20:1
|
20 | impl FromStr for A{}
| ^^^^^^^^^^^^^^^^^^^^ missing `Err`, `from_str` in implementation
|
= note: type Err;
= note: fn from_str(&str) -> std::result::Result<Self, <Self as std::str::FromStr>::Err>;
error[E0046]: not all trait items implemented, missing: `Foo`, `foo`, `bar`, `bay`
--> foo.rs:22:1
|
22 | impl X<usize> for A {
| ^ missing `Foo`, `foo`, `bar`, `bay` in implementation
|
= note: type Foo;
= note: fn foo() -> T;
= note: fn bar();
= note: fn bay<'lifetime, TypeParameterA>(a: usize, b: u8);
error: aborting due to 3 previous errors
```
Fixes rust-lang#24626
For a given file `foo.rs`:
```rust
struct A {}
impl std::fmt::Display for A {
fn fmt() -> () {}
}
```
provide the expected method signature:
```bash
error: main function not found
error[E0186]: method `fmt` has a `&self` declaration in the trait, but not in the impl
--> foo.rs:4:5
|
4 | fn fmt() -> () {}
| ^^^^^^^^^^^^^^^^^ expected `&self` in impl
|
= note: Expected signature: fn fmt(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error>;
= note: Found signature: fn fmt();
error: aborting due to previous error
```
Fixes rust-lang#28011
|
Related: #37370. |
steveklabnik
removed
the
T-compiler
|
Worth pointing out that the signature is relatively easy to get today if the method is removed. Still a problem though. |
bors
added a commit
that referenced
this issue
Jun 4, 2017
Show trait method signature when impl differs
When the trait's span is available, it is already being used, add a
`note` for the cases where the span isn't available:
<pre>
error[E0053]: <b>method `fmt` has an incompatible type for trait</b>
--> $DIR/trait_type.rs:17:4
|
17 | fn fmt(&self, x: &str) -> () { }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ in mutability
|
= note: expected type `<b>fn(&MyType, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error></b>`
found type `<b>fn(&MyType, &str)</b>`
error[E0050]: <b>method `fmt` has 1 parameter but the declaration in trait `std::fmt::Display::fmt` has 2</b>
--> $DIR/trait_type.rs:21:11
|
21 | fn fmt(&self) -> () { }
| ^^^^^ expected 2 parameters, found 1
|
= note: `fmt` from trait: `<b>fn(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error></b>`
error[E0186]: <b>method `fmt` has a `&self` declaration in the trait, but not in the impl</b>
--> $DIR/trait_type.rs:25:4
|
25 | fn fmt() -> () { }
| ^^^^^^^^^^^^^^^^^^ expected `&self` in impl
|
= note: `fmt` from trait: `<b>fn(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error></b>`
error[E0046]: <b>not all trait items implemented, missing: `fmt`</b>
--> $DIR/trait_type.rs:28:1
|
28 | impl std::fmt::Display for MyType4 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `fmt` in implementation
|
= note: `fmt` from trait: `<b>fn(&Self, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error></b>`
</code></pre>
Fix #28011.
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# to comment
When implementing a trait, it would be useful to see the expected method signature in compiler error messages. Example
The current error message for E0186 only lets me partially resolve the issue:
It would be more friendly to the user if the message showed both the actual and expected method signatures.
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