workspace folders are configured twice at startup

[FlorianKroiss]

During initialization of the language server, we already transmit the workspace folders, see

lsp4e/org.eclipse.lsp4e/src/org/eclipse/lsp4e/LanguageServerWrapper.java

Line 433 in bbf499f

initParams.setWorkspaceFolders(getRelevantWorkspaceFolders());

When we are done with the initialization, we immediately schedule a job to send a WorkspaceFoldersChangeEvent with same projects again, see:

lsp4e/org.eclipse.lsp4e/src/org/eclipse/lsp4e/LanguageServerWrapper.java

Lines 727 to 746 in bbf499f

	private void watchProjects() {
	if (!supportsWorkspaceFolderCapability()) {
	return;
	}
	final LanguageServer currentLS = context.languageServer;
	new WorkspaceJob("Setting watch projects on server " + serverDefinition.label) { //$NON-NLS-1$
	@Override
	public IStatus runInWorkspace(@Nullable IProgressMonitor monitor) throws CoreException {
	final var wsFolderEvent = new WorkspaceFoldersChangeEvent();
	wsFolderEvent.getAdded().addAll(getRelevantWorkspaceFolders());
	if (currentLS != null && currentLS == context.languageServer) {
	currentLS.getWorkspaceService()
	.didChangeWorkspaceFolders(new DidChangeWorkspaceFoldersParams(wsFolderEvent));
	}
	ResourcesPlugin.getWorkspace().addResourceChangeListener(workspaceFolderUpdater,
	IResourceChangeEvent.POST_CHANGE | IResourceChangeEvent.PRE_DELETE | IResourceChangeEvent.PRE_CLOSE);
	return Status.OK_STATUS;
	}
	}.schedule();
	}

Depending on how the language server handles a WorkspaceFoldersChangeEvent, this might degrade the initial responsiveness of the LS quite a bit.
For example, basedpyright has to remove all workspace folders only to add them all back again.

[sebthom]

I've seen that too. I wonder if there are edge cases that require this? @mickaelistria ?

[mickaelistria]

I don't think the current implementation that duplicates workspaceFolders is intentional; but I remember of some LS that require the list in initializationOptions and will ignore the notifications, and some LS doing it the other way round. However, it's a long time ago now and I don't know which LS were examples of those behaviors nor whether this still holds true now.

However, I wouldn't treat it as a bug, telling workspaceFolders multiple times is no illegal. The LS should be implemented to consider that; ie instead of re-loading tons of things on workspaceFolders notification, compare with the current state and only process what needs to be changed.