7904: Improved completion sorting r=JoshMcguigan a=JoshMcguigan
I was working on extending #3954 to apply completion scores in more places (I'll have another PR open for that soon) when I discovered that actually completion sorting was not working for me at all in `coc.nvim`. This led me down a bit of a rabbit hole of how coc and vs code each sort completion items.
Before this PR, rust-analyzer was setting the `sortText` field on completion items to `None` if we hadn't applied any completion score for that item, or to the label of the item with a leading whitespace character if we had applied any completion score. Completion score is defined in rust-analyzer as an enum with two variants, `TypeMatch` and `TypeAndNameMatch`.
In vs code the above strategy works, because if `sortText` isn't set [they default it to the label](b4ead4ed66). However, coc [does not do this](e211e36147/src/completion/complete.ts (L245)).
I was going to file a bug report against coc, but I read the [LSP spec for the `sortText` field](https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_completion) and I feel like it is ambiguous and coc could claim what they do is a valid interpretation of the spec.
Further, the existing rust-analyzer behavior of prepending a leading whitespace character for completion items with any completion score does not handle sorting `TypeAndNameMatch` completions above `TypeMatch` completions. They were both being treated the same.
The first change this PR makes is to set the `sortText` field to either "1" for `TypeAndNameMatch` completions, "2" for `TypeMatch` completions, or "3" for completions which are neither of those. This change works around the potential ambiguity in the LSP spec and fixes completion sorting for users of coc. It also allows `TypeAndNameMatch` items to be sorted above just `TypeMatch` items (of course both of these will be sorted above completion items without a score).
The second change this PR makes is to use the actual completion scores for ref matches. The existing code ignored the actual score and always assumed these would be a high priority completion item.
#### Before
Here coc just sorts based on how close the items are in the file.
#### After
Here we correctly get `zzz` first, since that is both a type and name match. Then we get `ccc` which is just a type match.
Co-authored-by: Josh Mcguigan <joshmcg88@gmail.com>
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