Adverse interaction between `unreachable` code, `type: ignore[...]`, and `pass` or `...`

[finite-state-machine]

Bug Report

Both pass statements and the ellipsis (...) are treated as non-statements by mypy, leading to unexpected handling of an unreachable cases.

To Reproduce

Run the following with --strict --warn-unreachable:

mypy-play.net gist

def func1(value: int) -> None:
    if not isinstance(value, int):
        pass  # type: ignore[unreachable]       # error: [unused-ignore]
        print("there was a problem ...")        # error: [unreachable]

Changing pass to a literal ellipsis (...) also reproduces this problem.

(Motivation: since # type: ignore[...] directives must appear on the same line they affect, placing the # type directive on a pass statement can avoid very long lines.)

Expected Behavior

mypy should treat pass as the unreachable statement in this case.

Actual Behavior

mypy's output is:

main.py:3: error: Unused "type: ignore" comment  [unused-ignore]
main.py:4: error: Statement is unreachable  [unreachable]
Found 2 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.5.1
• Mypy command-line flags: --strict --warn-unreachable
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.8, 3.11