untitled - use ref counted lifecycle

[bpasero]

Fixes #192356

This starts to use references for untitled text model lifecycle. Upon revert, the model gets reset to be empty but not disposed. Those that create the reference dispose it by listening to the revert.

[bpasero]

@jrieken might need your help with the failing test [Bug] Failed to create new test file when in an untitled file #1261.

[jrieken]

@bpasero I debugged into this and what is happens is the following

• the workspace edit for a new file is dispatched
• this makes its way into BulkTextEdits
• per file/uri we create an EditTask which holds a reference to the respected model
• when the edit task is done the model reference is released/disposed
• since nobody else is holding a reference the model is disposed again
• the integration test now fails because the disposed model doesn't have any contents (anymore)

It feels that someone, e.g the workbench, should also reference the newly created model so that a tab is opened for it?

[bpasero]

Yeah, good finding. We do track dirty untitled models and force open them, but with a delay of 800ms to reduce the spam this can generate when the editor is then actually saved shortly after:

vscode/src/vs/workbench/contrib/files/browser/editors/textFileEditorTracker.ts

Line 44 in f75db45

this._register(this.textFileService.untitled.onDidChangeDirty(model => this.ensureDirtyFilesAreOpenedWorker.work(model.resource)));

Even when I change that to open instantly, the test fails and that is probably due to the async nature of the editor opening.

Then I remember how this issue is addressed with file models, which are model reference backed. We prevent disposal of the underlying model until the dirty state is changed. Otherwise we would see a similar issue with text files.

I pushed a change to adopt this concept also for untitled files and the test seems to pass now.