The `[unreachable]` check fails for module scope code and allows unreachable raising of Exceptions

[harahu]

Bug Report

There are seemingly trivial cases of unreachable code not being detected at module level, or when the code consists of raise statements.

To Reproduce

from typing import Final
from typing import NoReturn


def foo() -> NoReturn:
 raise Exception("foo")


def bar() -> NoReturn:
 foo()

 # Should trigger [unreachable] but doesn't
 raise Exception("I shouldn't pass static analysis")


def baz() -> NoReturn:
 raise Exception("baz")

 # Should trigger [unreachable] but doesn't
 raise Exception("I shouldn't pass static analysis")


def qux() -> None:
 foo()

 # Should trigger [unreachable] but doesn't
 raise Exception("I shouldn't pass static analysis")


foo()

# Should trigger [unreachable] but doesn't
raise Exception("foo")

# Should trigger [unreachable] but doesn't(!)
MEANING: Final[int] = 42

Expected Behavior

As seen in my example, I would expect the optional [unreachable] check to detect the following examples of unreachable code:

• General module level code following an exception being raised directly, or a NoReturn callable being called.
• Unreachable exception raising (occurring after some prior exception having been raised)

Actual Behavior

The example above type checks with warn_unreachable = True.

Your Environment

• Mypy version used: 0.910
• Mypy command-line flags: n/a
• Mypy configuration options from mypy.ini (and other config files):

[mypy]
python_version = 3.8
pretty = True
warn_redundant_casts = True
warn_unused_ignores = True
ignore_missing_imports = True
strict_optional = True
no_implicit_optional = True
show_error_context = True
show_column_numbers = True
disallow_untyped_calls = True
disallow_untyped_defs = True
warn_return_any = True
warn_unreachable = True
show_none_errors = True
show_error_codes = True
follow_imports = normal
namespace_packages = True
explicit_package_bases = True

• Python version used: 3.8.10
• Operating system and version:
  Ubuntu 21.04