Mypy not treating an empty Dict in a tuple as matching Iterable[Dict[..., ...]]

[sethmlarson]

Bug Report

Mypy is treating an empty dictionary in a tuple differently than an empty dictionary in other collections when it comes to matching Iterable[Dict[..., ...]].

Expected Behavior

With the given file:

from typing import Iterable, Dict, Any


def f(x: Iterable[Dict[str, str]]) -> None:
    pass


# Lists all work as expected
f([])
f([{}])
f([{"k": "v"}])

# Empty tuple works
f(())

# Tuple of empty dict doesn't work
f(({},))

# Tuple with non-empty dict works
f(({"k": "v"},))

and running mypy with --strict you should receive no errors because Tuple[Dict[empty]] should match Iterable[Dict[str, str]].

Actual Behavior

$ mypy --strict testme.py 
testme.py:17: error: Argument 1 to "f" has incompatible type "Tuple[Dict[<nothing>, <nothing>]]"; expected "Iterable[Dict[str, str]]"
Found 1 error in 1 file (checked 1 source file)

which is erroring out on this line:

f(({},))

Your Environment

• Mypy version used: 0.910
• Mypy command-line flags: --strict
• Python version used: 3.8.6
• Operating system and version: Ubuntu 20.04

This is potentially related to #6613 where an empty collection isn't matching a collection type?

[JelleZijlstra]

Also similar to #11618 (I suspect @hauntsaninja's explanation there applies here too).

[erictraut]

This bug appears to have been fixed. I'm not able to repro it with mypy 1.5.

[hauntsaninja]

Fixed by #13406