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suggest adding parameters to exactly match the trait definition #107548

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9 changes: 9 additions & 0 deletions compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
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Expand Up @@ -1404,6 +1404,15 @@ fn compare_number_of_method_arguments<'tcx>(
potentially_plural_count(trait_number_args, "parameter")
),
);
if let Ok(snip) = tcx.sess.source_map().span_to_snippet(trait_span) {
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@compiler-errors compiler-errors Feb 1, 2023

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This just copies the contents of the parentheses, right? If so, this doesn't take params into account, I think:

trait Foo {
  fn bar<T>(_: T);
}

impl Foo for () {
  fn bar<E>(_: E, _: i32) {}
}

which would suggest changing fn bar<E>(_: T) {}

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@lyming2007 lyming2007 Feb 1, 2023

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yes it would suggest:

error[E0050]: method `bar` has 2 parameters but the declaration in trait `Foo::bar` has 1
 --> params.rs:6:16
  |
2 |   fn bar<T>(_: T);
  |                - trait requires 1 parameter
...
6 |   fn bar<E>(_: E, _: i32) {}
  |                ^^^^^^^^^ expected 1 parameter, found 2
  |
help: modify the signature to match the trait definition
  |
6 |   fn bar<E>(_: T) {}

I think we should suggest it to be fn bar<E>(_: E) {} or fn bar<T>(_: T) {}

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@compiler-errors compiler-errors Feb 1, 2023

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Similarly, we need to consider cases where the arguments reference generics from the trait:

trait Foo<T> {
  fn foo(_: T);
}

impl Foo<()> for i32 {
  fn foo();
}

Should suggest _: (), not _: T.

let args_suggestion = if trait_number_args != 0 { snip } else { "".to_string() };
err.span_suggestion_verbose(
impl_span,
"modify the signature to match the trait definition",
format!("{}", args_suggestion),
Applicability::HasPlaceholders,
);
}
} else {
err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
}
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3 changes: 3 additions & 0 deletions tests/ui/error-codes/E0050.rs
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Expand Up @@ -8,8 +8,11 @@ struct Bar;

impl Foo for Bar {
fn foo(&self) -> bool { true } //~ ERROR E0050
//~| HELP: modify the signature to match the trait definition
fn bar(&self) { } //~ ERROR E0050
//~| HELP: modify the signature to match the trait definition
fn less(&self, x: u8, y: u8, z: u8) { } //~ ERROR E0050
//~| HELP: modify the signature to match the trait definition
}

fn main() {
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19 changes: 17 additions & 2 deletions tests/ui/error-codes/E0050.stderr
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Expand Up @@ -6,24 +6,39 @@ LL | fn foo(&self, x: u8) -> bool;
...
LL | fn foo(&self) -> bool { true }
| ^^^^^ expected 2 parameters, found 1
|
help: modify the signature to match the trait definition
|
LL | fn foo(&self, x: u8) -> bool { true }
| ~~~~~~~~~~~~

error[E0050]: method `bar` has 1 parameter but the declaration in trait `Foo::bar` has 4
--> $DIR/E0050.rs:11:12
--> $DIR/E0050.rs:12:12
|
LL | fn bar(&self, x: u8, y: u8, z: u8);
| -------------------------- trait requires 4 parameters
...
LL | fn bar(&self) { }
| ^^^^^ expected 4 parameters, found 1
|
help: modify the signature to match the trait definition
|
LL | fn bar(&self, x: u8, y: u8, z: u8) { }
| ~~~~~~~~~~~~~~~~~~~~~~~~~~

error[E0050]: method `less` has 4 parameters but the declaration in trait `Foo::less` has 1
--> $DIR/E0050.rs:12:13
--> $DIR/E0050.rs:14:13
|
LL | fn less(&self);
| ----- trait requires 1 parameter
...
LL | fn less(&self, x: u8, y: u8, z: u8) { }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected 1 parameter, found 4
|
help: modify the signature to match the trait definition
|
LL | fn less(&self) { }
| ~~~~~

error: aborting due to 3 previous errors

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11 changes: 11 additions & 0 deletions tests/ui/impl-trait/in-trait/method-signature-matches.stderr
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Expand Up @@ -50,6 +50,12 @@ LL | fn calm_down_please() -> impl Sized;
...
LL | fn calm_down_please(_: (), _: (), _: ()) {}
| ^^^^^^^^^^^^^^^^ expected 0 parameters, found 3
|
help: modify the signature to match the trait definition
|
LL - fn calm_down_please(_: (), _: (), _: ()) {}
LL + fn calm_down_please(_: ) {}
|

error[E0050]: method `come_on_a_little_more_effort` has 0 parameters but the declaration in trait `TooLittle::come_on_a_little_more_effort` has 3
--> $DIR/method-signature-matches.rs:38:5
Expand All @@ -59,6 +65,11 @@ LL | fn come_on_a_little_more_effort(_: (), _: (), _: ()) -> impl Sized;
...
LL | fn come_on_a_little_more_effort() {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected 3 parameters, found 0
|
help: modify the signature to match the trait definition
|
LL | (), _: (), _: () {}
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@compiler-errors compiler-errors Feb 1, 2023

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What happened here?

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@lyming2007 lyming2007 Feb 1, 2023

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oh. That's a bug of my implementation which doesn't consider the impl function being 0 parameters. I'll fix it

| ~~~~~~~~~~~~~~~~

error[E0053]: method `early` has an incompatible type for trait
--> $DIR/method-signature-matches.rs:47:27
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1 change: 1 addition & 0 deletions tests/ui/trait-method-number-parameters.rs
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Expand Up @@ -5,6 +5,7 @@ trait Foo {
impl Foo for i32 {
fn foo(
&mut self, //~ ERROR
//~| HELP: modify the signature to match the trait definition
x: i32,
) {
}
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6 changes: 6 additions & 0 deletions tests/ui/trait-method-number-parameters.stderr
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Expand Up @@ -5,8 +5,14 @@ LL | fn foo(&mut self, x: i32, y: i32) -> i32;
| ------------------------- trait requires 3 parameters
...
LL | / &mut self,
LL | |
LL | | x: i32,
| |______________^ expected 3 parameters, found 2
|
help: modify the signature to match the trait definition
|
LL | &mut self, x: i32, y: i32,
| ~~~~~~~~~~~~~~~~~~~~~~~~~

error: aborting due to previous error

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1 change: 1 addition & 0 deletions tests/ui/traits/impl-different-num-params.rs
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Expand Up @@ -4,6 +4,7 @@ trait Foo {
impl Foo for isize {
fn bar(&self) -> isize {
//~^ ERROR method `bar` has 1 parameter but the declaration in trait `Foo::bar` has 2
//~| HELP: modify the signature to match the trait definition
*self
}
}
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5 changes: 5 additions & 0 deletions tests/ui/traits/impl-different-num-params.stderr
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Expand Up @@ -6,6 +6,11 @@ LL | fn bar(&self, x: usize) -> Self;
...
LL | fn bar(&self) -> isize {
| ^^^^^ expected 2 parameters, found 1
|
help: modify the signature to match the trait definition
|
LL | fn bar(&self, x: usize) -> isize {
| ~~~~~~~~~~~~~~~

error: aborting due to previous error

Expand Down