Don't suggest unstable items on stable toolchain
Closes#3020
This PR implements stability check in `ide-completion` so that unstable items are only suggested if you're on nightly toolchain.
It's a bit unfortunate `CompletionContext::check_stability()` is spammed all over the crate, but we should call it before building `CompletionItem` as you cannot get attributes on the item it's completing from that struct. I looked up every callsite of `Builder::add_to()`, `Completions::add[_opt]()`, and`Completions::add_all()` and inserted the check wherever necessary.
The tests are admittedly incomplete in that I didn't add tests for every kind of item as I thought that would be too big and not worthwhile. I copy-pasted some existing basic tests in every test module and adjusted them.
Drop support for non-syroot proc macro ABIs
This makes some bigger changes to how we handle the proc-macro-srv things, for one it is now an empty crate if built without the `sysroot-abi` feature, this simplifies some things dropping the need to put the feature cfg in various places. The cli wrapper now actually depends on the server, instead of being part of the server that is just exported, that way we can have a true dummy server that just errors on each request if no sysroot support was specified.
minor: Fix some simple FIXMEs
Each FIXME fix has been split into its own commit, since they're all pretty independent changes.
(Forgot to open a PR for this a few days ago, oops)
internal: Implement Structured API for snippets
Fixes#11638 (including moving the cursor before the generated type parameter)
Adds `add_tabstop_{before,after}` for inserting tabstop snippets before & after nodes, and `add_placeholder_snippet` for wrapping nodes inside placeholder nodes.
Currently, the snippets are inserted into the syntax tree in `SourceChange::commit` so that snippet bits won't interfere with syntax lookups before completing a `SourceChange`.
It would be preferable if snippet rendering was deferred to after so that rendering can work directly with text ranges, but have left that for a future PR (it would also make it easier to finely specify which text edits have snippets in them).
Another possible snippet variation to support would be a group of placeholders (i.e. placeholders with the same tabstop number) so that a generated item and its uses can be renamed right as it's generated, which is something that is technically supported by the current snippet hack in VSCode, though it's not clear if that's a thing that is officially supported.
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.
