Rollup merge of rust-lang#105491 - sulami:master, r=compiler-errors

Illegal sized bounds: only suggest mutability change if needed

In a scenario like

```rust
struct Type;

pub trait Trait {
    fn function(&mut self)
    where
        Self: Sized;
}

impl Trait for Type {
    fn function(&mut self) {}
}

fn main() {
    (&mut Type as &mut dyn Trait).function();
}
```

the problem is Sized, not the mutability of self. Thus don't emit the "you need &T instead of &mut T" note, or the other way around, as all it does is just invert the mutability of whatever was supplied.

Fixes rust-lang#103622.

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -209,7 +209,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  ProbeScope::TraitsInScope,
  ) {
  Ok(ref new_pick) if pick.differs_from(new_pick) => {
- needs_mut = true;
+ needs_mut = new_pick.self_ty.ref_mutability() != self_ty.ref_mutability();
  }
  _ => {}
  }

src/test/ui/illegal-sized-bound/mutability-mismatch.rs

@@ -0,0 +1,34 @@
+struct MutType;
+
+pub trait MutTrait {
+ fn function(&mut self)
+ where
+ Self: Sized;
+ //~^ this has a `Sized` requirement
+}
+
+impl MutTrait for MutType {
+ fn function(&mut self) {}
+}
+
+struct Type;
+
+pub trait Trait {
+ fn function(&self)
+ where
+ Self: Sized;
+ //~^ this has a `Sized` requirement
+}
+
+impl Trait for Type {
+ fn function(&self) {}
+}
+
+fn main() {
+ (&MutType as &dyn MutTrait).function();
+ //~^ ERROR the `function` method cannot be invoked on a trait object
+ //~| NOTE you need `&mut dyn MutTrait` instead of `&dyn MutTrait`
+ (&mut Type as &mut dyn Trait).function();
+ //~^ ERROR the `function` method cannot be invoked on a trait object
+ //~| NOTE you need `&dyn Trait` instead of `&mut dyn Trait`
+}

src/test/ui/illegal-sized-bound/mutability-mismatch.stderr

@@ -0,0 +1,24 @@
+error: the `function` method cannot be invoked on a trait object
+ --> $DIR/mutability-mismatch.rs:28:33
+ |
+LL | Self: Sized;
+ | ----- this has a `Sized` requirement
+...
+LL | (&MutType as &dyn MutTrait).function();
+ | ^^^^^^^^
+ |
+ = note: you need `&mut dyn MutTrait` instead of `&dyn MutTrait`
+
+error: the `function` method cannot be invoked on a trait object
+ --> $DIR/mutability-mismatch.rs:31:35
+ |
+LL | Self: Sized;
+ | ----- this has a `Sized` requirement
+...
+LL | (&mut Type as &mut dyn Trait).function();
+ | ^^^^^^^^
+ |
+ = note: you need `&dyn Trait` instead of `&mut dyn Trait`
+
+error: aborting due to 2 previous errors
+

src/test/ui/illegal-sized-bound/regular.rs

@@ -0,0 +1,32 @@
+struct MutType;
+
+pub trait MutTrait {
+ fn function(&mut self)
+ where
+ Self: Sized;
+ //~^ this has a `Sized` requirement
+}
+
+impl MutTrait for MutType {
+ fn function(&mut self) {}
+}
+
+struct Type;
+
+pub trait Trait {
+ fn function(&self)
+ where
+ Self: Sized;
+ //~^ this has a `Sized` requirement
+}
+
+impl Trait for Type {
+ fn function(&self) {}
+}
+
+fn main() {
+ (&mut MutType as &mut dyn MutTrait).function();
+ //~^ ERROR the `function` method cannot be invoked on a trait object
+ (&Type as &dyn Trait).function();
+ //~^ ERROR the `function` method cannot be invoked on a trait object
+}

src/test/ui/illegal-sized-bound/regular.stderr

@@ -0,0 +1,20 @@
+error: the `function` method cannot be invoked on a trait object
+ --> $DIR/regular.rs:28:41
+ |
+LL | Self: Sized;
+ | ----- this has a `Sized` requirement
+...
+LL | (&mut MutType as &mut dyn MutTrait).function();
+ | ^^^^^^^^
+
+error: the `function` method cannot be invoked on a trait object
+ --> $DIR/regular.rs:30:27
+ |
+LL | Self: Sized;
+ | ----- this has a `Sized` requirement
+...
+LL | (&Type as &dyn Trait).function();
+ | ^^^^^^^^
+
+error: aborting due to 2 previous errors
+