INTERNAL ERROR with NoReturn in a boolean operation

[KotlinIsland]

from typing import NoReturn

a: NoReturn
a or 1

>mypy -V
mypy 0.920+dev.01e6aba30c787c664ac88d849b45f7d303316951

traceback

>mypy --show-traceback test.py
test.py:4: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.920+dev.01e6aba30c787c664ac88d849b45f7d303316951
Traceback (most recent call last):
  File "...\Python\Python310\lib\runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "...\Python\Python310\lib\runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "...\venv\Scripts\mypy.exe\__main__.py", line 7, in <module>
    sys.exit(console_entry())
  File "...\venv\lib\site-packages\mypy\__main__.py", line 12, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "...\venv\lib\site-packages\mypy\main.py", line 96, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "...\venv\lib\site-packages\mypy\main.py", line 173, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "...\venv\lib\site-packages\mypy\build.py", line 180, in build
    result = _build(
  File "...\venv\lib\site-packages\mypy\build.py", line 256, in _build
    graph = dispatch(sources, manager, stdout)
  File "...\venv\lib\site-packages\mypy\build.py", line 2715, in dispatch
    process_graph(graph, manager)
  File "...\venv\lib\site-packages\mypy\build.py", line 3046, in process_graph
    process_stale_scc(graph, scc, manager)
  File "...\venv\lib\site-packages\mypy\build.py", line 3144, in process_stale_scc
    graph[id].type_check_first_pass()
  File "...\venv\lib\site-packages\mypy\build.py", line 2180, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "...\venv\lib\site-packages\mypy\checker.py", line 319, in check_first_pass
    self.accept(d)
  File "...\venv\lib\site-packages\mypy\checker.py", line 425, in accept
    stmt.accept(self)
  File "...\venv\lib\site-packages\mypy\nodes.py", line 1087, in accept
    return visitor.visit_expression_stmt(self)
  File "...\venv\lib\site-packages\mypy\checker.py", line 3332, in visit_expression_stmt
    self.expr_checker.accept(s.expr, allow_none_return=True, always_allow_any=True)
  File "...\venv\lib\site-packages\mypy\checkexpr.py", line 3972, in accept
    typ = node.accept(self)
  File "...\venv\lib\site-packages\mypy\nodes.py", line 1828, in accept
    return visitor.visit_op_expr(self)
  File "...\venv\lib\site-packages\mypy\checkexpr.py", line 2197, in visit_op_expr
    return self.check_boolean_op(e, e)
  File "...\venv\lib\site-packages\mypy\checkexpr.py", line 2867, in check_boolean_op
    assert left_map is not None  # find_isinstance_check guarantees this
AssertionError:
test.py:4: : note: use --pdb to drop into pdb

[hauntsaninja]

Interesting. Something should probably return UninhabitedType.

[hauntsaninja]

Yeah, looks like even:

from typing import NoReturn

def f() -> NoReturn: ...

if f():
    pass
else:
    pass

breaks the "guarantee" of

mypy/mypy/checker.py

Line 4382 in 4e34fec

Guaranteed to not return None, None. (But may return {}, {})