Get "select virtual environment for the worskpace" prompt to show up regardless of pythonpath setting

[luabud]

#4908 but right now we're displaying it only only if there isn't an interpreter path set in the settings.json file. We should display it also when a global interpreter (i.e. not a virtual environment) is set there.

[DonJayamanne]

Prescribed solution

• Display prompt regardless (currently we have an if condition that displays prompt only if no interpreter has been selected.

[ericsnowcurrently]

[using the most recent insiders build of the extension ("2019.9.33401-rc")]
[3 "system" Pythons installed: 2.7, 3.6, and 3.7]

I was able to verify that, if "python.pythonPath" is not set in my workspace settings.json file, I get prompted to switch to the new environment (a la #4908). However, if "python.pythonPath" is set then I still do not get prompted.

steps:

1. create a new workspace with an empty "spam.py"
2. verify that settings.json is empty
3. in the workspace directory run python3 -m venv .venv

4. click on "no" (not on "stop prompting me")
5. verify that settings.json is still empty
6. click on the Python version in the status bar and pick one of the system Pythons
7. verify that settings.json now has a "python.pythonPath" entry
8. delete the .venv directory created in step 3
9. in the workspace directory run python3 -m venv .venv

At this point I expected to be prompted, but was not.

(possibly related: #7132)

[ericsnowcurrently]

FWIW, if I reload the window between steps 8 and 9 then it works as expected.

[ericsnowcurrently]

This is likely an upstream VS Code issue. It is ignoring the re-creation of the .venv directory at step 9. From what Kartik said, this isn't a problem on Windows (I'm testing on Linux).

details

Order of events:

1. src/client/interpreter/locators/services/workspaceVirtualEnvWatcherService.ts
   • during activation we register an "onDidCreate" event handler on a new filesystem watcher
   • we only watch for files named "python" (or "python.exe" on Windows)
   • we create an internal event to indicate that a new virtual environment was created
2. src/client/interpreter/virtualEnvs/virtualEnvPrompt.ts
   • we register a handler on that internal event
3. src/client/interpreter/locators/services/workspaceVirtualEnvWatcherService.ts
   • if the filesystem watcher emits the "onDidCreate" event for files named "python" then we fire the internal event
4. src/client/interpreter/virtualEnvs/virtualEnvPrompt.ts
   • if the internal event is fired then the handler (maybe) creates the prompt

I tried debugging this. First I checked to see if that "internal" event was fired. It did for step 1 in my earlier comment. For step 9 it did not. So then I checked to see if the filesystem watcher fired the "onDidCreate" event for step 9. It did not.

This means that, on linux at least, the filesystem watcher (upstream VS Code code) is ignoring the re-creation of the .venv directory. I wouldn't be surprised if there is some sort of cache involved which isn't getting flushed when the directory is deleted in step 8. This does not seem to be a problem on Windows.

Also, all the events fire properly if I create a new virtual environment with a different name.

[ericsnowcurrently]

We're okay to consider this validated. Aside from the corner case I found, everything works as expected (i.e. if I move step 6 to right before step 3). After talking with @luabud, we're okay to release with the edge case. I'll open a separate issue (#7147) to track it.