Provide API to retrieve or listen for registered document formatter IDs

[adalinesimonian]

Issue Type: Feature Request

It'd be great to have a way in the VS Code API of retrieving which document formatters are currently registered or a notification for when a document formatter is registered.

Over at vscode-stylelint we have e2e tests that start up VS Code and test various extension features, one of which is document formatting. However, there doesn't seem to be a way to know for certain that document formatting has been registered before executing the test. As a result, while changing the extension's activation event from * to onStartupFinished, the document formatter test has become flaky.

In other tests, we are able to retrieve and wait on whatever it is we want tested, such as, for example, a command. However, the only instance I've been able to find of code that is able to the same or similar with document formatters is part of the private API. If something similar, whether notification- or polling-based, existed, it'd perfectly fit this use case.

If I've missed any similar API endpoints that are already in place, please feel free to let me know!

VS Code version: Code 1.61.2 (6cba118, 2021-10-19T14:57:20.575Z)
OS version: Windows_NT x64 10.0.22000
Restricted Mode: No

[jrieken]

Over at vscode-stylelint we have e2e tests that start up VS Code and test various extension features, one of which is document formatting.

Is that your extension e2e? Iff so could know by exposing an API from you extension to those tests right?

[adalinesimonian]

We didn't have an API yet, so I:

• Added a notification to the language server that's emitted once a formatter is registered with the client
• Added an API to the extension that emits an event when it receives the formatter registration notification from the server
• Added a beforeAll to the formatter test that waits until the formatter registration event is emitted from the extension's public API

It definitely works, but it feels clunky having to add a notification to an editor-agnostic language server for testing purposes in a specific editor.

I won't bikeshed, though, if an API endpoint for getting document formatters by ID or something similar to the same effect is not something y'all are interested in adding or accepting as a contribution.

[jrieken]

Yeah, it is that we don't have plans to expose such API - we try to keep it minimal and its purpose is to drive the editor itself, not so much be infrastructure.

Given this is all e2e an easier approach might be simply self-activate your extension in tests (see Extension#activate. This requires that your extension registers its formatter during activate but most do

[adalinesimonian]

Yeah, it is that we don't have plans to expose such API - we try to keep it minimal and its purpose is to drive the editor itself, not so much be infrastructure.

Totally fair.

Given this is all e2e an easier approach might be simply self-activate your extension in tests (see Extension#activate. This requires that your extension registers its formatter during activate but most do

The extension is being activated in time — we have a global beforeAll that makes sure it is — rather, it's the delay between the extension's activation and the formatter being registered dynamically by the language server that was causing the test failures. But we're good for now with this workaround; hopefully, if anyone comes across this issue with a similar problem this discussion will be helpful for them.