Extend tests for dataclass hashability

Author: AlexWaygood

conformance/tests/dataclasses_hash.py

@@ -3,15 +3,19 @@
 """
 
 from dataclasses import dataclass
-from typing import Hashable
+from typing import Hashable, assert_type
 
 
 @dataclass
 class DC1:
     a: int
 
 
-# This should generate an error because DC1 isn't hashable.
+assert_type(DC1.__hash__, None)
+
+# These should generate errors because DC1 isn't hashable.
+DC1(0).__hash__()  # E
+hash(DC1(0))  # E
 v1: Hashable = DC1(0)  # E
 
 
@@ -20,15 +24,26 @@ class DC2:
     a: int
 
 
-v2: Hashable = DC2(0)
+# Because `DC2` is frozen, type checkers should synthesize
+# a callable `__hash__` method for it, and therefore should
+# emit a diagnostic here:
+assert_type(DC2.__hash__, None)  # E
+
+DC2(0).__hash__()  # OK
+hash(DC2(0))  # OK
+v2: Hashable = DC2(0)  # OK
 
 
 @dataclass(eq=True)
 class DC3:
     a: int
 
 
-# This should generate an error because DC3 isn't hashable.
+assert_type(DC3.__hash__, None)
+
+# These should generate errors because DC3 isn't hashable.
+DC3(0).__hash__()  # E
+hash(DC3(0))  # E
 v3: Hashable = DC3(0)  # E
 
 
@@ -37,15 +52,29 @@ class DC4:
     a: int
 
 
-v4: Hashable = DC4(0)
+# Because `DC4` is frozen, type checkers should synthesize
+# a callable `__hash__` method for it, and therefore should
+# emit a diagnostic here:
+assert_type(DC4.__hash__, None)  # E
+
+DC4(0).__hash__()  # OK
+hash(DC4(0))  # OK
+v4: Hashable = DC4(0)  # OK
 
 
 @dataclass(eq=True, unsafe_hash=True)
 class DC5:
     a: int
 
 
-v5: Hashable = DC5(0)
+# Type checkers should synthesize a callable `__hash__`
+# method for `DC5` due to `unsafe_hash=True`, and therefore
+# should emit a diagnostic here:
+assert_type(DC5.__hash__, None)  # E
+
+DC5(0).__hash__()  # OK
+hash(DC5(0))  # OK
+v5: Hashable = DC5(0)  # OK
 
 
 @dataclass(eq=True)
@@ -56,7 +85,13 @@ def __hash__(self) -> int:
         return 0
 
 
-v6: Hashable = DC6(0)
+# Type checkers should respect the manually defined `__hash__`
+# method for `DC6`, and therefore should emit a diagnostic here:
+assert_type(DC6.__hash__, None)  # E
+
+DC6(0).__hash__()  # OK
+hash(DC6(0))  # OK
+v6: Hashable = DC6(0)  # OK
 
 
 @dataclass(frozen=True)
@@ -67,4 +102,11 @@ def __eq__(self, other) -> bool:
         return self.a == other.a
 
 
-v7: Hashable = DC7(0)
+# Because `DC7` is frozen, type checkers should synthesize
+# a callable `__hash__` method for it, and therefore should
+# emit a diagnostic here:
+assert_type(DC7.__hash__, None)  # E
+
+DC7(0).__hash__()  # OK
+hash(DC7(0))  # OK
+v7: Hashable = DC7(0)  # OK