Manually defined R and Python environments

It's currently possible to specify specific R and Python paths to discover, but reviewing support tickets around interpreter discovery and startup in Positron, we often find that more flexibility around startup is needed. Because we don't have very many tools to customize interpreter startup that are scoped to a particular interpreter, there's no escape hatch if our existing tools don't provide the startup customization that's desired.

For example, it's easy to set an environment variable for all interpreters, but not a specific interpreter.

We recently added support for r-versions for R, which adds many extensibility points, but this mechanism (a) doesn't work for Python, and (b) relies on a file-based configuration that is effectively legacy configuration in Workbench.

Proposal

Add a settings.json based configuration mechanism that is similar to r-versions but cross-language and Positron-native, giving users the ability to specify an interpreter with a:

• label
• path to binary
• custom environment variables to set/amend
• custom startup command
• module to load
• repository to use
• library paths

etc.