`onDidChangeTabs` fires before `vscode.window.activeTextEditor` has been updated

[mjbvz]

1. In an extension, listen for vscode.window.tabGroups.onDidChangeTabs
2. Switch between editor tabs in a single editor group

Bug
When the event is fired, if I check vscode.window.activeTextEditor I see that the active editor is still for the previous tab. It seems like visibleTextEditors is correctly updated

Here I've just switched from x2.ts to x.ts and have paused on the call to onDidChangeTabs

[lramos15]

Hmm.. I think this is a tough one to fix. It's sort of the reason we've avoided saying the tabs API has anything to do with textEditors because a tab is not guaranteed to have a text editor backing it at any given time. We listen to lower level events so it's possible the tab becomes available while the document is still being constructed and therefore a tab API event can fire before something like activeTextEditor properly updates.

@jrieken and I discussed a lot of this and the ordering that was needed to make this process feel natural. Also I believe he owns the textEditor API so want to get his thoughts.

[jrieken]

I see that the active editor is still for the previous tab. It seems like visibleTextEditors is correctly updated

That would be surprising because visible and active editors are updated with one IPC call. It would mean the workbench hasn't updated yet, e.g the "new" tab still shows the "old" document...