April 2016's Issue #33174 called out the E0446 diagnostics as
confusing. While adding the name of the restricted type to the message
(548e681f) clarified matters somewhat, Esteban Küber pointed out that we
could stand to place a secondary span on the restricted type.
Here, we differentiate between crate-visible, truly private, and
otherwise restricted types, and place a secondary span specifically on
the visibility modifier of the restricted type's declaration (which we
can do now that HIR visibilities have spans!).
At long last, this resolves#33174.
- Recover from struct parse error on match and point out missing match
body.
- Point at struct when finding non-identifier while parsing its fields.
- Add label to "expected identifier, found {}" error.
Given the following statement
```rust
pub (a) fn afn() {}
```
Provide the following diagnostic:
```rust
error: incorrect restriction in `pub`
--> file.rs:15:1
|
15 | pub (a) fn afn() {}
| ^^^^^^^
|
= help: some valid visibility restrictions are:
`pub(crate)`: visible only on the current crate
`pub(super)`: visible only in the current module's parent
`pub(in path::to::module)`: visible only on the specified path
help: to make this visible only to module `a`, add `in` before the path:
| pub (in a) fn afn() {}
```
Remove cruft from old `pub(path)` syntax.
