boolean return inferred as Any return type

[Avasam]

Bug Report

A method returning only boolean values is inferred as returning Any

To Reproduce

See the following minimal example:

def is_valid_hwnd(hwnd: int):
    if not hwnd:
        return False
    return True
    
reveal_type(is_valid_hwnd(0)) # note: Revealed type is "Any"

The real-world example is as such:

def is_valid_hwnd(hwnd: int):
    """Validate the hwnd points to a valid window and not the desktop or whatever window obtained with `""`."""
    if not hwnd:
        return False
    if sys.platform == "win32":
        return bool(win32gui.IsWindow(hwnd) and win32gui.GetWindowText(hwnd))
    return True

Which is much more readable than a boolean expression. But even that surprisingly is inferred as Any:

def is_valid_hwnd(hwnd: int):
    return bool(hwnd and (sys.platform != "win32" or (win32gui.IsWindow(hwnd) and win32gui.GetWindowText(hwnd))))

Expected Behavior

The return type should be inferred as bool. Even Literal[True, False] or Literal[True, False] | bool would be fine.

Actual Behavior

Return type is inferred as Any

Your Environment

• Mypy version used: mypy 1.9.0 (compiled: yes)
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files):

; We don't run mypy in the CI. This is just to help anyone who would like to use it manually.
; Namely, the mypy_primer tool.
[mypy]
show_column_numbers = true
mypy_path = $MYPY_CONFIG_FILE_DIR/typings
implicit_reexport = true

strict = true
; Implicit return types !
check_untyped_defs = true
disallow_untyped_calls = false
disallow_untyped_defs = false
disallow_incomplete_defs = false
disable_error_code = return

; exclude mypyc build
exclude = .*(build)/.*

; Auto-generated code, not much we can do there
[mypy-gen.*]
disable_error_code = attr-defined, arg-type

; Of course my stubs are going to be incomplete. Otherwise they'd be on typeshed!
; Mypy becomes really whack with its errors inside these stubs though
[mypy-scipy.*]
disable_error_code = attr-defined, import-untyped

• Python version used: 3.11.6

[JelleZijlstra]

Duplicate of #10149