Spurious "Too many arguments" when unpacking empty dicts

[chkno]

mypy gives incorrect Too many arguments errors when unpacking empty dicts to zero-argument functions. Unpacking empty lists works fine.

from typing import Dict, List, NamedTuple

def f1():
    pass

class C1(NamedTuple):
    pass

d_zero: Dict[str,str] = {}

print((lambda: 42)(**{}))     # error: Too many arguments
print((lambda: 42)(**d_zero)) # error: Too many arguments

print(f1(**{}))     # error: Too many arguments for "f1"
print(f1(**d_zero)) # error: Too many arguments for "f1"

print(C1(**{}))     # error: Too many arguments for "C1"
print(C1(**d_zero)) # error: Too many arguments for "C1"

# Empty lists work fine in recent versions:
l_zero: List[str] = []
print((lambda: 42)(*[]))
print((lambda: 42)(*l_zero))
print(f1(*[]))
print(f1(*l_zero))
print(C1(*[]))
print(C1(*l_zero))

I observe this problem all three versions of mypy that I tried: 0.701 0.761 0.770. The list examples also incorrectly give errors in 0.701, but this has been fixed in 0.761 and 0.770.

[JukkaL]

Yeah, it seems that mypy should assume that the dictionary can be empty, for consistency with the list case.

[NeilGirdhar]

This looks like #4001