Fix explicit deref problems in closure capture
fix the `need-mut` part of #14562
Perhaps surprisingly, it wasn't unique immutable borrow. The code still doesn't emit any of them, and I think those won't happen in edition 2021 (which is currently the only thing implemented), since we always capture `&mut *x` instead of `&mut x`. But I'm not very sure about it.
Add doc-alias based completion
Closes#14406.
I adapted the parsing code from the CfgExpr parsing code, maybe there's a better abstraction for both, or attribute parsing in general. It also includes `doc(hidden)`-parsing, which means it could replace the other function.
There are a few tests for parsing.
`process_all_names` changed the most, I added some docs there to explain what happens.
Many call sites just pass an empy vec to `add_path_resolution`'s `doc_aliases`, since either it doesn't make sense to pass anything (e.g. visibility completion) or I don't know where to get them from. Shouldn't really matter, as it will just not show aliases if the vec is empty and we can extend alias completion in these cases later.
I added two tests in `special.rs` for struct name completion (which was the main thing I wanted). I also tried function and field names, but these don't work yet. I want to add those in a follow-up PR.
internal: add `as_slice` to `hir::Type`
~`remove_slice`~ `as_slice` is same as `remove_ref` but for slices.
Though there is `as_array` which I believe was named such because it also gets the length of the array, maybe. I am still shaky on the names feel free to suggest corrections.
internal: Rename `hir::diagnostics::MissingMatchArms.match_expr` field
`hir::diagnostics::MissingMatchArms.match_expr` had confusing name: it is pointing to scrutinee expression. Renamed to `scrutinee_expr` and used better fitting type for it.
Also small refactorings/cleanup.
MIR episode 2
This PR adds:
1. `need-mut` and `unused-mut` diagnostics
2. `View mir` command which shows MIR for the body under cursor, useful for debugging
3. MIR lowering for or-patterns and for-loops
