Do not suggest to add type annotations for unnameable types
Consider this example:
```rust
const A = || 42;
struct S<T> { t: T }
const B: _ = S { t: || 42 };
```
This currently produces the following output:
```
error: missing type for `const` item
--> src/lib.rs:1:7
|
1 | const A = || 42;
| ^ help: provide a type for the item: `A: [closure@src/lib.rs:1:11: 1:16]`
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> src/lib.rs:4:10
|
4 | const B: _ = S { t: || 42 };
| ^
| |
| not allowed in type signatures
| help: replace `_` with the correct type: `S<[closure@src/lib.rs:4:21: 4:26]>`
error: aborting due to 2 previous errors
```
However, these suggestions are obviously useless, because the suggested types cannot be written down. With my changes, the suggestion is replaced with a note, because there is no simple fix:
```
error: missing type for `const` item
--> test.rs:1:7
|
1 | const A = || 42;
| ^
|
note: however, the inferred type `[closure@test.rs:1:11: 1:16]` cannot be named
--> test.rs:1:11
|
1 | const A = || 42;
| ^^^^^
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> test.rs:4:10
|
4 | const B: _ = S { t: || 42 };
| ^ not allowed in type signatures
|
note: however, the inferred type `S<[closure@test.rs:4:21: 4:26]>` cannot be named
--> test.rs:4:14
|
4 | const B: _ = S { t: || 42 };
| ^^^^^^^^^^^^^^
error: aborting due to 2 previous errors
```
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