Add capability to ignore certain packages

[rchiodo]

Yes, I fully agree that we shouldn't treat transformers specially. What I meant is that maybe we could allow users to configure whether to ignore some specific packages? This way, when any package is poorly written (or the user just want it to be ignored for any reason), pylance can simply skip it (if configured) without affecting the analysis of other content.

Originally posted by @yueyinqiu in #7615

[rchiodo]

A potential way to implement this would be to virtualize the file system and prevent reads for the site-packages folder for the ignored package(s). This would be the same as if it wasn't installed but maybe that would work well enough?

[rchiodo]

Yeah it could allow reads of the directory structure but have all of the files just be empty

[yueyinqiu]

Thank you for acknowledging my suggestion. As I don't have a good understanding of how pylance actually works, I'm afraid I can't help much with the implementation details.

However, based on the current description, I have a concern: could it cause the checker to claim that a certain type does not exist, and report such errors? My personal expectation is more like resolving the entire module as Any, where we can import anything and use it in any way we want. (And Pylance doesn't check it and thus doesn't produce any errors for it, instead of assuming it doesn't exist.)

[rchiodo]

Yeah you're right it would show errors for unresolved imports. Much like this (I created the testlib package and an empty test_a file)

The problem would be special casing this ignored library. The 'ignore' setting we already have is for errors in a library, so it wouldn't work. And you'd still want the checker to run on your own source. So the checker itself would have to be wired to ignore errors in the specified package.

[yueyinqiu]

Yes, this might need to be specifically implemented.