reveal_type not run in "unreachable" branches

[hjwp]

Bug Report

It looks like reveal_type() doesn't work in "unreachable" branches, ie places where assert_never() passes.

To Reproduce

from typing import assert_never, reveal_type


def foo(b: bool):
    reveal_type(b)
    match b:
        case True:
            reveal_type(b)
            print("True")
        case False:
            reveal_type(b)
            print("False")
        case _:
            assert_never(b)
            reveal_type(b)  # this one does not print

(also at https://mypy-play.net/?mypy=latest&python=3.12&gist=d2646350c3ec4aa892763cdda7d32201)

Actual Behavior

❯ mypy thing.py
thing.py:5: note: Revealed type is "builtins.bool"
thing.py:8: note: Revealed type is "Literal[True]"
thing.py:11: note: Revealed type is "Literal[False]"
Success: no issues found in 1 source file

Expected behaviour

I would expect the 4th reveal_type() to print something like Revealed type is Never ?

(note that the assert_never() does "pass").

Your Environment

mypy 1.14.1 (compiled: yes)
Python 3.13.0 (also seen in 3.12)

[A5rocks]

This is intentional because mypy doesn't type check unreachable code. For instance, see also #18329.

[hjwp]

HI @A5rocks thanks for answering! I was confused because I thought assert_never() used the type checker, so implicitly the unreachable branch must be being type checked, and now i understand, i think -- assert_never() only causes a typing failure when the branch is not unreachable.

Shall we close this issue?

[A5rocks]

Tbh yeah this is tracked by that other issue.

(I'm not sure the specifics on how assert never works...)