`timezone.utc` isn't replaced when `datetime` isn't imported about django-upgrade HOT 4 CLOSED

See #389 (comment) and related issue for a similar problem, adding import is non trivial because it could be shadowed by anything named datetime in scope. safely doing that imply tracking scopes and declared named I suppose

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Actually I found a test case which matches my use case:

I have timezone imported, but no datetime import. I can see that test case was added in #227. Looks like it was intentionally decided to not handle this case, I assume there are some complications with adding a datetime import...

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Makes sense. I see that it's actually listed as a requirement for this fixer to work in the README. Going to close this, as I don't have a good suggestion on how to implement this safely... It seems relatively unlikely that something in scope is called datetime without having datetime imported, but it's probably better to err on the safe side.

As an inspiration, we might look at libCST, which has a fixer to add import.

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Their fixer seems to have the same issue, they don't really check scopes because it would be too expensive. See Instagram/LibCST#1024 (comment)

I agree, AddImportsVisitor won't be able to do a perfect job all the time unless we include expensive scope analysis into it

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