Recognize Iterator as Hashable

mypy/subtypes.py

@@ -1245,9 +1245,21 @@ def f(self) -> A: ...
         left = mypy.typeops.tuple_fallback(left)
     # We need to record this check to generate protocol fine-grained dependencies.
     type_state.record_protocol_subtype_check(left.type, right.type)
+    # Iterator instances inherit object.__hash__ at runtime, but Iterator is a
+    # protocol and therefore doesn't expose that inherited member structurally.
+    # Keep the special handling limited to the standard Hashable protocol: a
+    # concrete unhashable iterator must still be rejected. See #21813.
+    if is_named_instance(left, "typing.Iterator") and is_named_instance(right, "typing.Hashable"):
+        return True
     # nominal subtyping currently ignores '__init__' and '__new__' signatures
     members_not_to_check = {"__init__", "__new__"}
     members_not_to_check.update(skip)
+    # Iterator instances inherit object.__hash__ at runtime, but Iterator is a
+    # protocol and therefore doesn't expose that inherited member structurally.
+    # Keep the special handling limited to the standard Hashable protocol: a
+    # concrete unhashable iterator must still be rejected. See #21813.
+    if is_named_instance(left, "typing.Iterator") and is_named_instance(right, "typing.Hashable"):
+        members_not_to_check.add("__hash__")
     # Trivial check that circumvents the bug described in issue 9771:
     if left.type.is_protocol:
         members_right = set(right.type.protocol_members) - members_not_to_check

test-data/unit/check-protocols.test

@@ -1025,14 +1025,28 @@ main:15: note:         def [T2] a(self, other: P1[T2]) -> Any
 
 [case testHashable]
 
-from typing import Hashable, Iterable
+from typing import Hashable, Iterable, Iterator
 
 def f(x: Hashable) -> None:
     pass
 
 def g(x: Iterable[str]) -> None:
     f(x)   # E: Argument 1 to "f" has incompatible type "Iterable[str]"; expected "Hashable"
 
+def h(x: Iterator[str]) -> None:
+    f(x)
+
+class UnhashableIterator(Iterator[str]):
+    __hash__ = None  # type: ignore[assignment]
+
+    def __next__(self) -> str:
+        return ""
+
+def k(x: UnhashableIterator) -> None:
+    f(x)   # E: Argument 1 to "f" has incompatible type "UnhashableIterator"; expected "Hashable" \
+           # N: Following member(s) of "UnhashableIterator" have conflicts: \
+           # N:     __hash__: expected "Callable[[], int]", got "None"
+
 [builtins fixtures/object_hashable.pyi]
 [typing fixtures/typing-full.pyi]