Support code-action-on-save for triggering formatting

[rchl]

Current Version

0.10.0

Use-cases

Being able to format the document using the "code-action-on-save" editor feature. That feature is not really part of the spec. More an editor feature that is currently implemented by VSCode, LSP for Sublime Text, and probably others.

It works by user defining a setting like this one in the editor:

  "editor.codeActionsOnSave": {
    "source.fixAll.eslint": true,
    "source.organizeImports": true
  },

and the client requesting and applying such code actions from the server before saving.

Introducing a code action like source.format.terraform would allow to granularly enable "format-on-save" for that particular server rather than having to globally enable format-on-save (that utilizes formatting provider).

Attempted Solutions

It's currently possible to enable format-on-save in various editors by using its built-in format-on-save functionality that utilizes the server's documentFormattingProvider capabilities. The problem with that approach is that enabling that feature enables it for all servers and the user when running multiple servers, doesn't always want to enable it for all of them.

Proposal

Related LSP methods

The feature would utilize Code Action Request. The client makes a code action request with context.only set to source.format.terraform (for example), receives it back from the server and applies before saving the file. The code action could return a command to run (requires extra round trip) or ideally provide the edits directly.

The server capability codeActionProvider.codeActionKinds is also relevant and should be set by the server to include the source.format.terraform code action. That makes the code action available for both code-action-on-save and some context menus that editors might expose for the document.

References

[github-actions]

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