Skip to content

Commit c224da5

Browse files
tyrallatyralla
authored
Do not intersect types in isinstance checks if at least one is final (#16330)
Fixes #15148 I think it also fixes the [initial bug](#12163 (comment)) reported in #12163 (this is why I added a TypeVar test case) but not [this bug](#12163 (comment)) reported later in the same issue.
1 parent d54cc35 commit c224da5

File tree

3 files changed

+111
-3
lines changed

3 files changed

+111
-3
lines changed

‎mypy/checker.py‎

Lines changed: 11 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -5254,6 +5254,15 @@ def _make_fake_typeinfo_and_full_name(
52545254
pretty_names_list = pretty_seq(
52555255
format_type_distinctly(*base_classes, options=self.options, bare=True), "and"
52565256
)
5257+
5258+
new_errors = []
5259+
for base in base_classes:
5260+
if base.type.is_final:
5261+
new_errors.append((pretty_names_list, f'"{base.type.name}" is final'))
5262+
if new_errors:
5263+
errors.extend(new_errors)
5264+
return None
5265+
52575266
try:
52585267
info, full_name = _make_fake_typeinfo_and_full_name(base_classes, curr_module)
52595268
with self.msg.filter_errors() as local_errors:
@@ -5266,10 +5275,10 @@ def _make_fake_typeinfo_and_full_name(
52665275
self.check_multiple_inheritance(info)
52675276
info.is_intersection = True
52685277
except MroError:
5269-
errors.append((pretty_names_list, "inconsistent method resolution order"))
5278+
errors.append((pretty_names_list, "would have inconsistent method resolution order"))
52705279
return None
52715280
if local_errors.has_new_errors():
5272-
errors.append((pretty_names_list, "incompatible method signatures"))
5281+
errors.append((pretty_names_list, "would have incompatible method signatures"))
52735282
return None
52745283

52755284
curr_module.names[full_name] = SymbolTableNode(GDEF, info)

‎mypy/messages.py‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2051,7 +2051,7 @@ def redundant_expr(self, description: str, truthiness: bool, context: Context) -
20512051
def impossible_intersection(
20522052
self, formatted_base_class_list: str, reason: str, context: Context
20532053
) -> None:
2054-
template = "Subclass of {} cannot exist: would have {}"
2054+
template = "Subclass of {} cannot exist: {}"
20552055
self.fail(
20562056
template.format(formatted_base_class_list, reason), context, code=codes.UNREACHABLE
20572057
)

‎test-data/unit/check-narrowing.test‎

Lines changed: 99 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1020,6 +1020,105 @@ else:
10201020
reveal_type(true_or_false) # N: Revealed type is "Literal[False]"
10211021
[builtins fixtures/primitives.pyi]
10221022

1023+
1024+
[case testNarrowingIsInstanceFinalSubclass]
1025+
# flags: --warn-unreachable
1026+
1027+
from typing import final
1028+
1029+
class N: ...
1030+
@final
1031+
class F1: ...
1032+
@final
1033+
class F2: ...
1034+
1035+
n: N
1036+
f1: F1
1037+
1038+
if isinstance(f1, F1):
1039+
reveal_type(f1) # N: Revealed type is "__main__.F1"
1040+
else:
1041+
reveal_type(f1) # E: Statement is unreachable
1042+
1043+
if isinstance(n, F1): # E: Subclass of "N" and "F1" cannot exist: "F1" is final
1044+
reveal_type(n) # E: Statement is unreachable
1045+
else:
1046+
reveal_type(n) # N: Revealed type is "__main__.N"
1047+
1048+
if isinstance(f1, N): # E: Subclass of "F1" and "N" cannot exist: "F1" is final
1049+
reveal_type(f1) # E: Statement is unreachable
1050+
else:
1051+
reveal_type(f1) # N: Revealed type is "__main__.F1"
1052+
1053+
if isinstance(f1, F2): # E: Subclass of "F1" and "F2" cannot exist: "F1" is final \
1054+
# E: Subclass of "F1" and "F2" cannot exist: "F2" is final
1055+
reveal_type(f1) # E: Statement is unreachable
1056+
else:
1057+
reveal_type(f1) # N: Revealed type is "__main__.F1"
1058+
[builtins fixtures/isinstance.pyi]
1059+
1060+
1061+
[case testNarrowingIsInstanceFinalSubclassWithUnions]
1062+
# flags: --warn-unreachable
1063+
1064+
from typing import final, Union
1065+
1066+
class N: ...
1067+
@final
1068+
class F1: ...
1069+
@final
1070+
class F2: ...
1071+
1072+
n_f1: Union[N, F1]
1073+
n_f2: Union[N, F2]
1074+
f1_f2: Union[F1, F2]
1075+
1076+
if isinstance(n_f1, F1):
1077+
reveal_type(n_f1) # N: Revealed type is "__main__.F1"
1078+
else:
1079+
reveal_type(n_f1) # N: Revealed type is "__main__.N"
1080+
1081+
if isinstance(n_f2, F1): # E: Subclass of "N" and "F1" cannot exist: "F1" is final \
1082+
# E: Subclass of "F2" and "F1" cannot exist: "F2" is final \
1083+
# E: Subclass of "F2" and "F1" cannot exist: "F1" is final
1084+
reveal_type(n_f2) # E: Statement is unreachable
1085+
else:
1086+
reveal_type(n_f2) # N: Revealed type is "Union[__main__.N, __main__.F2]"
1087+
1088+
if isinstance(f1_f2, F1):
1089+
reveal_type(f1_f2) # N: Revealed type is "__main__.F1"
1090+
else:
1091+
reveal_type(f1_f2) # N: Revealed type is "__main__.F2"
1092+
[builtins fixtures/isinstance.pyi]
1093+
1094+
1095+
[case testNarrowingIsSubclassFinalSubclassWithTypeVar]
1096+
# flags: --warn-unreachable
1097+
1098+
from typing import final, Type, TypeVar
1099+
1100+
@final
1101+
class A: ...
1102+
@final
1103+
class B: ...
1104+
1105+
T = TypeVar("T", A, B)
1106+
1107+
def f(cls: Type[T]) -> T:
1108+
if issubclass(cls, A):
1109+
reveal_type(cls) # N: Revealed type is "Type[__main__.A]"
1110+
x: bool
1111+
if x:
1112+
return A()
1113+
else:
1114+
return B() # E: Incompatible return value type (got "B", expected "A")
1115+
assert False
1116+
1117+
reveal_type(f(A)) # N: Revealed type is "__main__.A"
1118+
reveal_type(f(B)) # N: Revealed type is "__main__.B"
1119+
[builtins fixtures/isinstance.pyi]
1120+
1121+
10231122
[case testNarrowingLiteralIdentityCheck]
10241123
from typing import Union
10251124
from typing_extensions import Literal

0 commit comments

Comments
 (0)