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Crash in union with a forward reference to a bad type. #4543
Description
This code causes a crash:
Alias = Union[Bad, C, D]
Bad = object()
class C:
pass
class D:
pass
option: Alias
if isinstance(option, C):
passHere is a traceback:
tmp.py:3: error: Invalid type "tmp.Bad"
tmp.py:13: error: INTERNAL ERROR -- please report a bug at https://github.com/python/mypy/issues version: 0.570-dev-d2c04190b8d407476c535f30d07a9f6712e7b12a-dirty
Traceback (most recent call last):
File "/Users/ilevkivskyi/mypy/bin/mypy", line 11, in <module>
load_entry_point('mypy===0.570-dev-d2c04190b8d407476c535f30d07a9f6712e7b12a-dirty', 'console_scripts', 'mypy')()
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/__main__.py", line 7, in console_entry
main(None)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/main.py", line 80, in main
type_check_only(sources, bin_dir, options, flush_errors)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/main.py", line 129, in type_check_only
flush_errors=flush_errors)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/build.py", line 172, in build
result = _build(sources, options, alt_lib_path, bin_dir, saved_cache, flush_errors)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/build.py", line 258, in _build
graph = dispatch(sources, manager)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/build.py", line 2048, in dispatch
process_graph(graph, manager)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/build.py", line 2349, in process_graph
process_stale_scc(graph, scc, manager)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/build.py", line 2525, in process_stale_scc
graph[id].type_check_first_pass()
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/build.py", line 1923, in type_check_first_pass
self.type_checker().check_first_pass()
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/checker.py", line 228, in check_first_pass
self.accept(d)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/checker.py", line 323, in accept
stmt.accept(self)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/nodes.py", line 928, in accept
return visitor.visit_if_stmt(self)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/checker.py", line 2232, in visit_if_stmt
if_map, else_map = self.find_isinstance_check(e)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/checker.py", line 2835, in find_isinstance_check
return conditional_type_map(expr, vartype, type)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/checker.py", line 3191, in conditional_type_map
remaining_type = restrict_subtype_away(current_type, proposed_precise_type)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/subtypes.py", line 817, in restrict_subtype_away
new_items = [item for item in t.relevant_items()
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/subtypes.py", line 818, in <listcomp>
if (not (is_proper_subtype(erase_type(item), erased_s) or
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/erasetype.py", line 25, in erase_type
return typ.accept(EraseTypeVisitor())
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/types.py", line 194, in accept
return visitor.visit_unbound_type(self)
File "/Users/ilevkivskyi/mypy/lib/python3.6/site-packages/mypy/erasetype.py", line 31, in visit_unbound_type
assert False, 'Not supported'
AssertionError: Not supported
It looks like the problem is that clearly erroneous types are not wrapped in ForwardRef and are not post-processed in third pass. There are two options that I see now for UnboundTypes (maybe there are other):
- Expect them in type checker and amend the corresponding visitors
- Replace them with
Anyafter giving anInvalid typeerror (maybe with better error message, but we already have an issue for this.)
I would prefer the second option, since this seems simpler and would probably minimize the amount of not useful errors (because of the initially invalid type).
Activity
ilevkivskyi commentedon Feb 5, 2018
Note: It looks like the crash happens only if there are at least three elements in the union.
ilevkivskyi commentedon Mar 7, 2018
Another possible scenario for this crash is #4653
Remove an assert triggered by UnboundType leaking from semanal.py (#5258