Fall back to the next priority when defaultEnvManager has no environment for a scope #2000

Written with Claude Code (AI-assisted) and reviewed by me.

Request

When python-envs.defaultEnvManager names a manager that has no environment for a given scope, fall through to the next priority (python.defaultInterpreterPath, then auto-discovery) instead of selecting nothing.

That would make a single user-level setting mean "use this manager where it applies, otherwise behave as usual", which is what you want with project-scoped managers like Pixi or Hatch.

Current behaviour

With "python-envs.defaultEnvManager": "renan-r-santos.pixi-code:pixi" in user settings (Windows 11, Python Environments 1.42.0, Pixi Code 0.2.0):

• The Pixi project folder correctly gets its Pixi environment.
• The global scope gets nothing, because a Pixi manager has no global environment:

  [interpreterSelection] global: none (source: defaultEnvManager)
  

  Anything outside the workspace folders (the Settings editor, a file from a parent folder, an untitled file) then has no interpreter, and the Python extension shows "An Invalid Python interpreter is selected" even though the workspace's environment is valid.
• By the same logic, opening any non-Pixi project (e.g. one with a .venv) would select nothing for it as well.

The only way to avoid this today is to set defaultEnvManager per workspace in every Pixi project, which loses the convenience of a user-level default.

Where this happens

In src/features/interpreterSelection.ts, resolvePriorityChainCore returns as soon as the manager named by defaultEnvManager is registered (return { result: { manager, source: 'defaultEnvManager' }, errors }). applyInitialEnvironmentSelection then uses result.manager.get(scope) as the environment, including when it's undefined.

Possible approaches

1. Fall through in the priority chain: if the manager from pythonProjects[] / defaultEnvManager returns no environment for the scope, continue with priority 3 and then 4, and record the source accordingly. This would be generic and would cover every third-party manager.
2. Document a contract for managers: isExplicitSelection already describes managers that "have no environment of their own" returning "a fallback owned by another manager", which the built-in venv manager does. If that's the intended design, third-party managers (Pixi, Hatch) could be asked to do the same, and the API docs for EnvironmentManager.get() could say so.

Option 1 seems more robust to me, since each extension would otherwise have to re-implement fallback logic. But I'd like to know which direction you prefer before proposing a PR.

Related

• Startup selection stays on a fallback environment when the configured defaultEnvManager registers late #1997 / Re-apply environment selection when a configured manager registers late #1998: late registration of third-party managers at startup (a different problem with the same setup).
• What is the global environment for? #1485: question from the Hatch extension's author about what the global scope is for with third-party managers.
• Warning environment manager pixi is not registered prefix-dev/pixi-code#44: Pixi-side report about defaultEnvManager and the "not registered" warning.