Failing to concatenate fix lengths tuples if the tuple depends on a variable

[knatten]

I believe this is a bug. Reproduced with mypy 0.761 on Ubuntu 18.04.

In this code:

def breaks(self) -> None:
    var = True
    t = ("a","b") + (("c","d") if var else tuple())

def works(self) -> None:
    t = ("a","b") + (("c","d") if True else tuple())

The works function works fine, but the breaks function breaks with the following error:

$ mypy tuple_if.py 
tuple_if.py:3: error: No overload variant of "__add__" of "tuple" matches argument type "object"
tuple_if.py:3: note: Possible overload variants:
tuple_if.py:3: note:     def __add__(self, Tuple[str, ...]) -> Tuple[str, ...]
tuple_if.py:3: note:     def __add__(self, Tuple[Any, ...]) -> Tuple[Any, ...]
Found 1 error in 1 file (checked 1 source file)

I would expect the behaviour to be the same in both functions.

[intgr]

Hi! I think this is a duplicate of #4975 and is fixed by #8333 (already merged). It hasn't been released though, if you're feeling adventurous you could try reproducing this with the master branch.

[knatten]

@JukkaL since you closed this issue, did you test whether this is fixed on master?

[intgr]

✅ I tested it now, result was: Success: no issues found in 1 source file

[knatten]

Nice, thanks for testing!