Use AnnotatedTextEdits throughout HLS

[michaelpj]

AnnotatedTextEdits are a feature of the LSP spec that allow more structured edits to be returned. In particular:

• Multiple edits can be associated with a single annotation
• The annotation can have a name and a description
• The annotation can also indicate that the edit requires confirmation from the user

I haven't tested out what this looks like in the client, but in principle this should allow much nicer communication of what's going on with edits. For example, when adding imports for completions, we can annotate the edits for modifying imports to say what we're doing. The confirmation feature (if it actually works) seems nice for questionable or wide-ranging edits, like for renaming across modules.

We should try using them!

A good place to start would be here: https://github.com/haskell/haskell-language-server/blob/master/plugins/hls-refactor-plugin/src/Development/IDE/Plugin/CodeAction.hs#L202, which sends a message to the user to tell them what we did. Hopefully an AnnotatedTextEdit would do that job better.

[nilsalex]

I would be interested in working on this @fendor

[michaelpj]

Did you get anywhere @nilsalex ?

[michaelpj]

See microsoft/vscode#151240

[michaelpj]

We will need to not send these if clients don't understand them. I had an idea for that. We can always translate an AnnotatedTextEdit into a TextEdit. So just before sending the response, we can check if the client supports what we're sending and downgrade it if it doesn't support that. I guess we can do this in combineResponses although that's somewhat gross.

We could potentially do this with something like this:

class Conform (m :: Method t k) where
  type Caps :: *
  caps :: Lens' ClientCapabilities Caps
  conform :: Caps -> ResponseResult m -> ResponseResult m

i.e. for a given method, given the capabilities relevant to that method, try to make the result we produced acceptable to the client by downgrading things.

This could probably live in lsp... and here's the issue I wrote, even: haskell/lsp#367

[nilsalex]

I played around with it a bit @michaelpj, switching to AnnotatedTextEdits for import list extensions (the place you suggested above).

Without requiring confirmation, I could not see any visual difference, neither in VS Code, nor with coc.nvim. With confirmation required, VS Code shows a list of changes before optionally applying them. I'll push my experiments to my fork.

[michaelpj]

That's a shame. I wish there was some guide in the spec showing what editors support what features, and what they actually do...