No "missing return" error in function declared "-> X" where X is Any due to missing import

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
32/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Start with the reported reproducer and run mypy with --ignore-missing-imports to confirm that the missing return is not reported when the annotation resolves to Any. Trace how missing-import types affect return checking, then add or update a regression test showing the expected diagnostic and run the relevant mypy test suite.

Written by the indexing model from the issue text.

Description

feature needs discussion priority-1-normal
input
import arbitrary_module

def f() -> arbitrary_module.MyType:
    x = 1
    y = 2

# reveal_type(arbitrary_module.MyType)
output
$ mypy test.py --ignore-missing-imports
$ echo $?
0
expected (?)
test.py:3: error: Missing return statement
explanation

I get why this is happening, just feels non-ideal to me.

The revealed type above is Any, and implicit return None matches Any so this is allowed. The case I'd like to prevent is the accidental omission of a return statement here (this example has been reduced from an actual production issue).

From an implementation perspective I guess I'd want the types generated from --ignore-missing-imports to be non-nullable, though this might be a big change.

I'm sure there's a duplicate of this issue but I was struggling to search for it :S

Dominant language
Python
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