Keep track of when DVC repo is locked

[rogermparent]

Related to #230 and #231

In order to implement user-friendly UI elements that are disabled when we know that they'll fail, we'll need to keep track of when the DVC repo is locked.

I would think this is as easy as adding a vscode file watcher for the dvc lockfile.

[mattseddon]

Is there a related DVC issue for this?

I.e are they investigating not locking the repo for readonly options?

[shcheklein]

I.e are they investigating not locking the repo for readonly options?

good question. Probably not exactly related to this specific issue though? We will still need a mechanism to detect and disable certain actions (and show the message). Or allow and fail gracefully. Any of those approaches is fine to me. WDYT?

cc @yalozhkin

[shcheklein]

Aslo, how does Git extension behave when repo is locked?

[rogermparent]

We will still need a mechanism to detect and disable certain actions (and show the message). Or allow and fail gracefully. Any of those approaches is fine to me. WDYT?

I think there's no getting around needing to gracefully handle when DVC is called while locked. We'll probably even want to handle different commands in different ways: roughly, light read-only commands like exp show could silently attempt a retry while commands that mutate the repo or just take a while like exp apply or exp run would provide an error message with feedback.

I believe we could also use showErrorMessage's generic items API to add clickable options for rich handling of these errors (like a "retry" option on lock errors)

[mattseddon]

@rogermparent I think we can track this under #643, WDYT?

[mattseddon]

Duplicate of #643 and better covered by #772, closing for now.