Should use of `use` (rather than `import`) always generate a warning with `--warn-unstable`?

[bradcray]

Something I've been wondering about recently is whether using the use statement should always generate an unstable warning—not because use itself is an unstable language concept, but because programs that rely on use are inherently unstable as the modules that they are using change and evolve. I say this as a huge proponent of use when sketching out code on a daily basis, but not in code that is being written to be stable / bulletproof over the long-term (which is where I think of --warn-unstable as being most valuable).

[lydia-duncan]

I think that'd muddy the definition of unstable for users, personally. This seems more appropriate for the linter, imo

[jabraham17]

This feels very similar to #26102, which proposes a lint warning for the same thing.

To me, an unstable warning for something thats not unstable because we might change something about it in the future is a very big hammer.

[bradcray]

To me, I think it depends on whether you think of --warn-unstable as meaning "Warn me about unstable language/library features I'm using" (arguably the current definition) vs. "Warn me about things in my code that might make it unstable over time" (which I'd argue is at least as useful). Is this a slippery slope? I'm not sure… I don't have other things in mind that would fit the second definition rather than the first.

[jabraham17]

I think changing the meaning of --warn-unstable to "Warn me about things in my code that might make it unstable over time" is a big change. It also breaks the meaning of "stable code".

If I am writing stable code, that means a compilation with --warn-unstable comes back clean. If we change the meaning of --warn-unstable to "maybe unstable", that changes what we define as stable code. So we are in effect making use statements unstable, which I don't think we want.

Wanting a flag that tells me "this might break in the future" seems similar to #27336, in the context of editions (where IMO this makes more sense).