Base {} Dict Should Infer from Function Return Type

Bug Report

I think this may be a possible refinement bug. Mypy flags an error on the assignment line, and not the return statement. So it is clear Mypy flags {} as a subtype of {str, str}, but I think this should be one of those cases where having refinements should reduce the annotation burden on developers. Unless we want to throw an error because of imprecision.

To Reproduce

# Ideally, a small sample program that demonstrates the problem.
# Or even better, a reproducible playground link https://mypy-play.net/ (use the "Gist" button)
def func() -> dict[str, str]: 
    x = {} ## error here for annot 
    return x

reproducible link: Gist Playground

Expected Behavior

I would expect Mypy to notice the reveal_type(x) as dict[str, str] based off the functions return type and not raise an error.

Actual Behavior

main.py:2: error: Need type annotation for "x" (hint: "x: dict[<type>, <type>] = ...")  [var-annotated]

Your Environment

• Mypy version used:
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used:

Start by running the main.py reproduction with strict flags through the linked mypy-play playground or Gist and confirm the var-annotated diagnostic. Done means mypy infers x as dict[str, str] from func's return type and no longer reports the annotation error, with regression coverage added for this behavior.