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Suggest changing impl parameter types to match trait
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This is particularly useful for cases where arbitrary self types are
used, like in custom `Future`s.
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@estebank
estebank committed Apr 8, 2021
1 parent d43ede1 commit 147649d
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Showing 12 changed files with 151 additions and 25 deletions.
50 changes: 43 additions & 7 deletions compiler/rustc_typeck/src/check/compare_method.rs
View file
Expand Up @@ -290,18 +290,55 @@ fn compare_predicate_entailment<'tcx>(
"method `{}` has an incompatible type for trait",
trait_m.ident
);
if let TypeError::ArgumentMutability(_) = terr {
if let Some(trait_err_span) = trait_err_span {
if let Ok(trait_err_str) = tcx.sess.source_map().span_to_snippet(trait_err_span)
match &terr {
TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0)
if trait_m.fn_has_self_parameter =>
{
let ty = trait_sig.inputs()[0];
let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty())
{
ExplicitSelf::ByValue => "self".to_owned(),
ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
ExplicitSelf::ByReference(_, hir::Mutability::Mut) => {
"&mut self".to_owned()
}
_ => format!("self: {}", ty),
};

// When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
// span points only at the type `Box<Self`>, but we want to cover the whole
// argument pattern and type.
let impl_m_hir_id =
tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
let span = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
ImplItemKind::Fn(ref sig, body) => tcx
.hir()
.body_param_names(body)
.zip(sig.decl.inputs.iter())
.map(|(param, ty)| param.span.to(ty.span))
.next()
.unwrap_or(impl_err_span),
_ => bug!("{:?} is not a method", impl_m),
};

diag.span_suggestion(
span,
"change the self-receiver type to match the trait",
sugg,
Applicability::MachineApplicable,
);
}
TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => {
if let Some(trait_ty) = trait_sig.inputs().get(*i) {
diag.span_suggestion(
impl_err_span,
"consider changing the mutability to match the trait",
trait_err_str,
"change the parameter type to match the trait",
trait_ty.to_string(),
Applicability::MachineApplicable,
);
}
}
_ => {}
}

infcx.note_type_err(
Expand Down Expand Up @@ -482,8 +519,7 @@ fn compare_self_type<'tcx>(
tcx.sess,
impl_m_span,
E0186,
"method `{}` has a `{}` declaration in the trait, but \
not in the impl",
"method `{}` has a `{}` declaration in the trait, but not in the impl",
trait_m.ident,
self_descr
);
Expand Down
23 changes: 23 additions & 0 deletions src/test/ui/compare-method/bad-self-type.rs
View file
@@ -0,0 +1,23 @@
use std::future::Future;
use std::task::{Context, Poll};

fn main() {}

struct MyFuture {}

impl Future for MyFuture {
type Output = ();
fn poll(self, _: &mut Context<'_>) -> Poll<()> {
//~^ ERROR method `poll` has an incompatible type for trait
todo!()
}
}

trait T {
fn foo(self);
}

impl T for MyFuture {
fn foo(self: Box<Self>) {}
//~^ ERROR method `foo` has an incompatible type for trait
}
30 changes: 30 additions & 0 deletions src/test/ui/compare-method/bad-self-type.stderr
View file
@@ -0,0 +1,30 @@
error[E0053]: method `poll` has an incompatible type for trait
--> $DIR/bad-self-type.rs:10:13
|
LL | fn poll(self, _: &mut Context<'_>) -> Poll<()> {
| ^^^^
| |
| expected struct `Pin`, found struct `MyFuture`
| help: change the self-receiver type to match the trait: `self: Pin<&mut MyFuture>`
|
= note: expected fn pointer `fn(Pin<&mut MyFuture>, &mut Context<'_>) -> Poll<_>`
found fn pointer `fn(MyFuture, &mut Context<'_>) -> Poll<_>`

error[E0053]: method `foo` has an incompatible type for trait
--> $DIR/bad-self-type.rs:21:18
|
LL | fn foo(self);
| ---- type in trait
...
LL | fn foo(self: Box<Self>) {}
| ------^^^^^^^^^
| | |
| | expected struct `MyFuture`, found struct `Box`
| help: change the self-receiver type to match the trait: `self`
|
= note: expected fn pointer `fn(MyFuture)`
found fn pointer `fn(Box<MyFuture>)`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0053`.
6 changes: 4 additions & 2 deletions src/test/ui/compare-method/reordered-type-param.stderr
View file
Expand Up @@ -5,8 +5,10 @@ LL | fn b<C:Clone,D>(&self, x: C) -> C;
| - type in trait
...
LL | fn b<F:Clone,G>(&self, _x: G) -> G { panic!() }
| - - ^ expected type parameter `F`, found type parameter `G`
| | |
| - - ^
| | | |
| | | expected type parameter `F`, found type parameter `G`
| | | help: change the parameter type to match the trait: `F`
| | found type parameter
| expected type parameter
|
Expand Down
6 changes: 4 additions & 2 deletions src/test/ui/impl-trait/impl-generic-mismatch-ab.stderr
View file
Expand Up @@ -5,8 +5,10 @@ LL | fn foo<A: Debug>(&self, a: &A, b: &impl Debug);
| -- type in trait
...
LL | fn foo<B: Debug>(&self, a: &impl Debug, b: &B) { }
| - ^^^^^^^^^^^ expected type parameter `B`, found type parameter `impl Debug`
| |
| - ^^^^^^^^^^^
| | |
| | expected type parameter `B`, found type parameter `impl Debug`
| | help: change the parameter type to match the trait: `&B`
| expected type parameter
|
= note: expected fn pointer `fn(&(), &B, &impl Debug)`
Expand Down
5 changes: 4 additions & 1 deletion src/test/ui/impl-trait/trait_type.stderr
View file
Expand Up @@ -2,7 +2,10 @@ error[E0053]: method `fmt` has an incompatible type for trait
--> $DIR/trait_type.rs:7:21
|
LL | fn fmt(&self, x: &str) -> () { }
| ^^^^ types differ in mutability
| ^^^^
| |
| types differ in mutability
| help: change the parameter type to match the trait: `&mut Formatter<'_>`
|
= note: expected fn pointer `fn(&MyType, &mut Formatter<'_>) -> Result<(), std::fmt::Error>`
found fn pointer `fn(&MyType, &str)`
Expand Down
2 changes: 1 addition & 1 deletion src/test/ui/issues/issue-13033.stderr
View file
Expand Up @@ -8,7 +8,7 @@ LL | fn bar(&mut self, other: &dyn Foo) {}
| ^^^^^^^^
| |
| types differ in mutability
| help: consider changing the mutability to match the trait: `&mut dyn Foo`
| help: change the parameter type to match the trait: `&mut dyn Foo`
|
= note: expected fn pointer `fn(&mut Baz, &mut dyn Foo)`
found fn pointer `fn(&mut Baz, &dyn Foo)`
Expand Down
15 changes: 12 additions & 3 deletions src/test/ui/issues/issue-20225.stderr
View file
Expand Up @@ -4,7 +4,10 @@ error[E0053]: method `call` has an incompatible type for trait
LL | impl<'a, T> Fn<(&'a T,)> for Foo {
| - this type parameter
LL | extern "rust-call" fn call(&self, (_,): (T,)) {}
| ^^^^ expected `&T`, found type parameter `T`
| ^^^^
| |
| expected `&T`, found type parameter `T`
| help: change the parameter type to match the trait: `(&'a T,)`
|
= note: expected fn pointer `extern "rust-call" fn(&Foo, (&'a T,))`
found fn pointer `extern "rust-call" fn(&Foo, (T,))`
Expand All @@ -15,7 +18,10 @@ error[E0053]: method `call_mut` has an incompatible type for trait
LL | impl<'a, T> FnMut<(&'a T,)> for Foo {
| - this type parameter
LL | extern "rust-call" fn call_mut(&mut self, (_,): (T,)) {}
| ^^^^ expected `&T`, found type parameter `T`
| ^^^^
| |
| expected `&T`, found type parameter `T`
| help: change the parameter type to match the trait: `(&'a T,)`
|
= note: expected fn pointer `extern "rust-call" fn(&mut Foo, (&'a T,))`
found fn pointer `extern "rust-call" fn(&mut Foo, (T,))`
Expand All @@ -27,7 +33,10 @@ LL | impl<'a, T> FnOnce<(&'a T,)> for Foo {
| - this type parameter
...
LL | extern "rust-call" fn call_once(self, (_,): (T,)) {}
| ^^^^ expected `&T`, found type parameter `T`
| ^^^^
| |
| expected `&T`, found type parameter `T`
| help: change the parameter type to match the trait: `(&'a T,)`
|
= note: expected fn pointer `extern "rust-call" fn(Foo, (&'a T,))`
found fn pointer `extern "rust-call" fn(Foo, (T,))`
Expand Down
15 changes: 12 additions & 3 deletions src/test/ui/issues/issue-35869.stderr
View file
Expand Up @@ -5,7 +5,10 @@ LL | fn foo(_: fn(u8) -> ());
| ------------ type in trait
...
LL | fn foo(_: fn(u16) -> ()) {}
| ^^^^^^^^^^^^^ expected `u8`, found `u16`
| ^^^^^^^^^^^^^
| |
| expected `u8`, found `u16`
| help: change the parameter type to match the trait: `fn(u8)`
|
= note: expected fn pointer `fn(fn(u8))`
found fn pointer `fn(fn(u16))`
Expand All @@ -17,7 +20,10 @@ LL | fn bar(_: Option<u8>);
| ---------- type in trait
...
LL | fn bar(_: Option<u16>) {}
| ^^^^^^^^^^^ expected `u8`, found `u16`
| ^^^^^^^^^^^
| |
| expected `u8`, found `u16`
| help: change the parameter type to match the trait: `Option<u8>`
|
= note: expected fn pointer `fn(Option<u8>)`
found fn pointer `fn(Option<u16>)`
Expand All @@ -29,7 +35,10 @@ LL | fn baz(_: (u8, u16));
| --------- type in trait
...
LL | fn baz(_: (u16, u16)) {}
| ^^^^^^^^^^ expected `u8`, found `u16`
| ^^^^^^^^^^
| |
| expected `u8`, found `u16`
| help: change the parameter type to match the trait: `(u8, u16)`
|
= note: expected fn pointer `fn((u8, _))`
found fn pointer `fn((u16, _))`
Expand Down
7 changes: 5 additions & 2 deletions src/test/ui/mismatched_types/E0053.stderr
View file
Expand Up @@ -5,7 +5,10 @@ LL | fn foo(x: u16);
| --- type in trait
...
LL | fn foo(x: i16) { }
| ^^^ expected `u16`, found `i16`
| ^^^
| |
| expected `u16`, found `i16`
| help: change the parameter type to match the trait: `u16`
|
= note: expected fn pointer `fn(u16)`
found fn pointer `fn(i16)`
Expand All @@ -20,7 +23,7 @@ LL | fn bar(&mut self) { }
| ^^^^^^^^^
| |
| types differ in mutability
| help: consider changing the mutability to match the trait: `&self`
| help: change the self-receiver type to match the trait: `self: &Bar`
|
= note: expected fn pointer `fn(&Bar)`
found fn pointer `fn(&mut Bar)`
Expand Down
7 changes: 5 additions & 2 deletions src/test/ui/mismatched_types/trait-impl-fn-incompatibility.stderr
View file
Expand Up @@ -5,7 +5,10 @@ LL | fn foo(x: u16);
| --- type in trait
...
LL | fn foo(x: i16) { }
| ^^^ expected `u16`, found `i16`
| ^^^
| |
| expected `u16`, found `i16`
| help: change the parameter type to match the trait: `u16`
|
= note: expected fn pointer `fn(u16)`
found fn pointer `fn(i16)`
Expand All @@ -20,7 +23,7 @@ LL | fn bar(&mut self, bar: &Bar) { }
| ^^^^
| |
| types differ in mutability
| help: consider changing the mutability to match the trait: `&mut Bar`
| help: change the parameter type to match the trait: `&mut Bar`
|
= note: expected fn pointer `fn(&mut Bar, &mut Bar)`
found fn pointer `fn(&mut Bar, &Bar)`
Expand Down
10 changes: 8 additions & 2 deletions src/test/ui/wrong-mul-method-signature.stderr
View file
Expand Up @@ -2,7 +2,10 @@ error[E0053]: method `mul` has an incompatible type for trait
--> $DIR/wrong-mul-method-signature.rs:16:21
|
LL | fn mul(self, s: &f64) -> Vec1 {
| ^^^^ expected `f64`, found `&f64`
| ^^^^
| |
| expected `f64`, found `&f64`
| help: change the parameter type to match the trait: `f64`
|
= note: expected fn pointer `fn(Vec1, f64) -> Vec1`
found fn pointer `fn(Vec1, &f64) -> Vec1`
Expand All @@ -11,7 +14,10 @@ error[E0053]: method `mul` has an incompatible type for trait
--> $DIR/wrong-mul-method-signature.rs:33:21
|
LL | fn mul(self, s: f64) -> Vec2 {
| ^^^ expected struct `Vec2`, found `f64`
| ^^^
| |
| expected struct `Vec2`, found `f64`
| help: change the parameter type to match the trait: `Vec2`
|
= note: expected fn pointer `fn(Vec2, Vec2) -> f64`
found fn pointer `fn(Vec2, f64) -> Vec2`
Expand Down

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