Python: Immediately start a Python runtime in Python workspaces

[seeM]

Via @petetronic:

If we find we are being opened in a Folder that is predominantly Python - perhaps we could start simple and just say we find .py files, or if there are better heuristics from the MS Python extension already - and just mark the preferred Python interpreter as Immediate

[petetronic]

Related to a request for R in #72

[petetronic]

Some activation events from the python extension include:

        "workspaceContains:mspythonconfig.json",
        "workspaceContains:pyproject.toml",
        "workspaceContains:Pipfile",
        "workspaceContains:setup.py",
        "workspaceContains:requirements.txt",
        "workspaceContains:manage.py",
        "workspaceContains:app.py"

[jmcphers]

We may be able to remove this hack once the Python extension accepts responsibility for starting Python when appropriate:

positron/src/vs/workbench/services/languageRuntime/common/languageRuntime.ts

Lines 459 to 482 in 707042f

	// --- Begin TEMPORARY ---
	// We want to start a Python runtime as a last-chance fallback if we have no other
	// runtimes to start. We consider this to be true under the following circumstances:
	//
	// - We have completed the discovery phase, which implies we've also started any
	// runtimes that asked to be started right away (startupBehavior === Immediate).
	// - No runtimes have been started or are running yet.
	// - This was not an initially untrusted workspace; in these workspaces, we don't
	// know what would have been automatically started, so we don't want to come
	// stomping in and starting a Python runtime.
	// - No runtimes will be automatically started for this workspace, i.e. this workspace
	// has no affiliated runtimes.
	//
	// This behavior shouldn't live here, but it does until the Python language pack
	// can be updated. See https://github.com/rstudio/positron/issues/1009
	if (this._discoveryPhase === LanguageRuntimeDiscoveryPhase.Complete &&
	!this.hasAnyStartedOrRunningRuntimes() &&
	languageRuntimeInfo.runtime.metadata.languageId === 'python' &&
	this._initiallyTrustedWorkspace === true &&
	!this._workspaceAffiliation.hasAffiliatedRuntime()) {
	this.autoStartRuntime(languageRuntimeInfo.runtime,
	`No other language runtimes want to start; Python is the default.`);
	}
	// --- End TEMPORARY ---

[seeM]

[...] once the Python extension accepts responsibility for starting Python when appropriate

@jmcphers I need to do some more testing to see whether activating eagerly actually brings Python into the discovery phase, I'd like to track that in #1009.

Until then, I think a good step for this issue for alpha would be:

1. Update R to only enable immediate startup if the workspace has R files, or if it's empty and the user has RStudio installed i.e. hasRFiles || (isEmpty && isRStudioUser).
2. Update Python to only enable immediate startup if the workspace contains Python files (including the non .py files Pete mentioned).

That way, R won't be started at all in folders that only contain Python files, and vice versa, until we figure out #1009. I've got branches of positron and positron-python running with this setup and I think it's a big improvement over the current behavior.

What do you think?

---

I also foresee a separate/related issue by looking at the code, but I haven't tested yet:

I'm not sure how Positron will currently react to multiple languages registering a runtime with immediate startup behavior (EDIT: all within the discovery phase). IIUC it would start whichever language happened to start register a runtime first. Is that a bug or intended?

positron/src/vs/workbench/services/languageRuntime/common/languageRuntime.ts

Lines 503 to 509 in a4ad542

	const languageRuntimeInfos = this._registeredRuntimes.filter(
	info => info.startupBehavior === LanguageRuntimeStartupBehavior.Immediate);
	if (languageRuntimeInfos.length) {
	this.autoStartRuntime(languageRuntimeInfos[0].runtime,
	`An extension requested the runtime to be started immediately.`);
	}
	}

[juliasilge]

I think hasRFiles() should return true with only R Markdown or Quarto files as well.

[seeM]

This is ready for review in 2023.09.0-139. It's worth testing in both R and Python projects. Note that this should only affect opening new workspaces