Do not attempt to provide an accurate suggestion for `impl Trait`
in bare trait types when linting. Instead, only do the object
safety check when an E0782 is already going to be emitted in the
2021 edition.
Fix#120241.
Note the parentheses in the last suggestion:
```
error[E0277]: the size for values of type `(dyn Foo + Send + 'static)` cannot be known at compilation time
--> $DIR/not-on-bare-trait.rs:7:8
|
LL | fn foo(_x: Foo + Send) {
| ^^ doesn't have a size known at compile-time
|
= help: the trait `Sized` is not implemented for `(dyn Foo + Send + 'static)`
= help: unsized fn params are gated as an unstable feature
help: you can use `impl Trait` as the argument type
|
LL | fn foo(_x: impl Foo + Send) {
| ++++
help: function arguments must have a statically known size, borrowed types always have a known size
|
LL | fn foo(_x: &(Foo + Send)) {
| ++ +
```
Add the following suggestions:
```
error[E0782]: trait objects must include the `dyn` keyword
--> $DIR/not-on-bare-trait-2021.rs:11:11
|
LL | fn bar(x: Foo) -> Foo {
| ^^^
|
help: use a generic type parameter, constrained by the trait `Foo`
|
LL | fn bar<T: Foo>(x: T) -> Foo {
| ++++++++ ~
help: you can also use `impl Foo`, but users won't be able to specify the type paramer when calling the `fn`, having to rely exclusively on type inference
|
LL | fn bar(x: impl Foo) -> Foo {
| ++++
help: alternatively, use a trait object to accept any type that implements `Foo`, accessing its methods at runtime using dynamic dispatch
|
LL | fn bar(x: &dyn Foo) -> Foo {
| ++++
error[E0782]: trait objects must include the `dyn` keyword
--> $DIR/not-on-bare-trait-2021.rs:11:19
|
LL | fn bar(x: Foo) -> Foo {
| ^^^
|
help: use `impl Foo` to return an opaque type, as long as you return a single underlying type
|
LL | fn bar(x: Foo) -> impl Foo {
| ++++
help: alternatively, you can return an owned trait object
|
LL | fn bar(x: Foo) -> Box<dyn Foo> {
| +++++++ +
```
- Either explicitly annotate `let x: () = expr;` where `x` has unit
type, or remove the unit binding to leave only `expr;` instead.
- Fix disjoint-capture-in-same-closure test
