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Fine grained crash when class is turned into a generic class #3279
Description
a.py:
import b
def f() -> b.C: passOriginal b.py:
import a
class C: passUpdated b.py:
from typing import TypeVar, Generic
import a
T = TypeVar('T')
class C(Generic[T]): pass
reveal_type(a.f)
c: C[int]
d = a.f()
d = c
c = dNow if I run mypy --quick a.py first with the original files, then with the updated b.py, I get a crash:
$ mypy --quick --show-traceback a.py
b.py:7: error: Revealed type is 'def () -> b.C'
/Users/jukka/src/mypy/b.py:11: error: INTERNAL ERROR -- please report a bug at https://github.com/python/mypy/issues version: 0.510-dev-c856a53fe06c0ad9193d86ab35fb86693940f273-dirty
Traceback (most recent call last):
File "/Users/jukka/src/mypy/scripts/mypy", line 6, in <module>
main(__file__)
File "/Users/jukka/src/mypy/mypy/main.py", line 46, in main
res = type_check_only(sources, bin_dir, options)
File "/Users/jukka/src/mypy/mypy/main.py", line 93, in type_check_only
options=options)
File "/Users/jukka/src/mypy/mypy/build.py", line 188, in build
graph = dispatch(sources, manager)
File "/Users/jukka/src/mypy/mypy/build.py", line 1570, in dispatch
process_graph(graph, manager)
File "/Users/jukka/src/mypy/mypy/build.py", line 1813, in process_graph
process_stale_scc(graph, scc, manager)
File "/Users/jukka/src/mypy/mypy/build.py", line 1912, in process_stale_scc
graph[id].type_check_first_pass()
File "/Users/jukka/src/mypy/mypy/build.py", line 1485, in type_check_first_pass
self.type_checker.check_first_pass()
File "/Users/jukka/src/mypy/mypy/checker.py", line 177, in check_first_pass
self.accept(d)
File "/Users/jukka/src/mypy/mypy/checker.py", line 262, in accept
stmt.accept(self)
File "/Users/jukka/src/mypy/mypy/nodes.py", line 853, in accept
return visitor.visit_assignment_stmt(self)
File "/Users/jukka/src/mypy/mypy/checker.py", line 1177, in visit_assignment_stmt
self.check_assignment(s.lvalues[-1], s.rvalue, s.type is None, s.new_syntax)
File "/Users/jukka/src/mypy/mypy/checker.py", line 1239, in check_assignment
rvalue_type = self.check_simple_assignment(lvalue_type, rvalue, lvalue)
File "/Users/jukka/src/mypy/mypy/checker.py", line 1698, in check_simple_assignment
rvalue_type = self.expr_checker.accept(rvalue, lvalue_type)
File "/Users/jukka/src/mypy/mypy/checkexpr.py", line 2056, in accept
typ = node.accept(self)
File "/Users/jukka/src/mypy/mypy/nodes.py", line 1213, in accept
return visitor.visit_name_expr(self)
File "/Users/jukka/src/mypy/mypy/checkexpr.py", line 123, in visit_name_expr
return self.narrow_type_from_binder(e, result)
File "/Users/jukka/src/mypy/mypy/checkexpr.py", line 2271, in narrow_type_from_binder
ans = narrow_declared_type(known_type, restriction)
File "/Users/jukka/src/mypy/mypy/meet.py", line 46, in narrow_declared_type
return meet_types(declared, narrowed)
File "/Users/jukka/src/mypy/mypy/meet.py", line 25, in meet_types
return t.accept(TypeMeetVisitor(s))
File "/Users/jukka/src/mypy/mypy/types.py", line 381, in accept
return visitor.visit_instance(self)
File "/Users/jukka/src/mypy/mypy/meet.py", line 198, in visit_instance
args.append(self.meet(t.args[i], si.args[i]))
IndexError: list index out of range
/Users/jukka/src/mypy/b.py:11: note: use --pdb to drop into pdb
Activity
JukkaL commentedon Apr 28, 2017
I can also cause a crash if I switch a generic class into a non-generic one. However, I need to switch the order of assignments in the second version:
ilevkivskyi commentedon Apr 28, 2017
I think this could be also a symptom of another problem: there are many places where e.g.
named_type('builtins.tuple')is used instead ofnamed_generic_type('builtins.tuple', [AnyType()]). So that many types with wrong type argument count are created. This leads to crashes like #3117. I think that ideally we could "fix" all such code, this process is started in #3129 (also in protocols PR I do the same fortyping.Awaitable).JukkaL commentedon Apr 29, 2017
These are all wrong. We should only create
Instancetypes with the correct number of type arguments, and crash hard if we try to create an bad type.ilevkivskyi commentedon Apr 29, 2017
OK, then a possible "robust" solution would be to remove
named_typeand only usenamed_generic_typethat will check argument count onInstancecreation. (We cannot make this check inInstance.__init__, since type argument counts are not known until third pass.)ilevkivskyi commentedon Dec 28, 2018
The quick mode was deprecated and is now removed, but now the same crash happens in the fine-grained mode. (Same files and the same traceback.)
ilevkivskyi commentedon Dec 28, 2018
(Removed the incremental label, since the crash doesn't happen in the normal incremental mode.)
ilevkivskyi commentedon Dec 28, 2018
Here is the full test case:
[-]Quick mode crash when class is turned into a generic class[/-][+]Fine grained crash when class is turned into a generic class[/+]Fix some daemon crashes involving classes becoming generic
Fix some daemon crashes involving classes becoming generic (#8157)