LSP: Advertise which CodeActionKinds the server supports to prevent blocking formatters in VS Code

[jvilk-stripe]

See microsoft/vscode#89745 and flow/flow-for-vscode#375

Flow version: 0.107.0 (although it's the same in new versions)

Expected behavior

Flow advertises which CodeActionKinds it supports during initialization:

https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_codeAction

Actual behavior

Flow advertises true or false, telling VS Code that it may support all code actions.

As a result, VS Code believes the Flow extension supports "source.fixAll" code actions, which is a non-standard code action that can block formatters like Prettier from running:

https://code.visualstudio.com/api/references/vscode-api#CodeActionKind

Since Flow can be slow to respond to code action requests when typechecking edits, users can see a multi-second wait before Prettier runs in VS Code.

This is only an issue if the user configures VS Code to apply "fixall" code actions before save. Unfortunately for Flow, the VS Code ESLint extension now uses source.fixAll code actions to surface ESLint fixups, and encourages users to configure VS Code to apply all ESLint fixups on save:

https://github.com/Microsoft/vscode-eslint#release-notes

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

This setting tells VS Code "apply all fixups for the range covered by a diagnostic with source eslint". Thus, VS Code queries all code action providers for JavaScript that support source.fixAll code actions to see if they have fixes for diagnostics with "source" set to "eslint" -- including flow. These requests block prettier from running.

A workaround is to disable code actions entirely in Flow.

• Link to Try-Flow or Github repo: