Simpler quick fix API

[mjbvz]

Follow up on #27614

Search terms

• code action / codeaction
• quick fix / quickfix
• getCodeFixes
• getSupportedCodeFixes

Problem

The getCodeFixes API currently takes a range plus a diagnostic code. Currently, the range we pass to it has to match the range of the diagnostic we are trying to fix. This API is difficult for editors to implement for a few reasons:

• We need to make multiple requests if we want to display quick fixes for multiple (potentially overlapping) diagnostics
• The editor has to ensure that the diagnostics as fully synchronized with the current text buffer state before making the request. It's easy for the editor's diagnostics to get temporarily out of sync with those on the server
• The editor has to keep around a list of diagnostics to make these requests

Proposal

We should consider a new quick fix API that addresses these problems and also is better aligned with the language server protocol. My proposal is that instead of having to think about diagnostics, editors pass the TS Server a range and are returned the valid quick fixes in that range.

Here's what the VS Code api for this looks like:

https://github.com/microsoft/vscode/blob/9a21b536639c2d986c50fb51b7da67bafdb50c9b/src/vs/vscode.d.ts#L2336

And here's the LSP:

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_codeAction

[mjbvz]

microsoft/vscode#117812 shows another case where a different API could help us ship a better user experience. Right now, you have to wait a moment to get fixes after you introduce an error in a file

[Kingwl]

Might also refactor?

[andrewbranch]

Updated URL for the LSP link in the issue body: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_codeAction

[justschen]

@navya9singh @DanielRosenwasser just an update - on the VS Code extension side of things, @mjbvz and I have added a fix to handle the issue when there are pending diagnostics at the point of re-requesting code actions microsoft/vscode#117812

this is currently in our latest insiders, but lmk if this leads to any issues with the changes in the API, or when those changes land!