Fix incorrect type inference for yield from with iterators

mypy/checkexpr.py

@@ -6273,7 +6273,13 @@ def visit_yield_from_expr(self, e: YieldFromExpr, allow_none_return: bool = Fals
         # Check that the iterator's item type matches the type yielded by the Generator function
         # containing this `yield from` expression.
         expected_item_type = self.chk.get_generator_yield_type(return_type, False)
-        actual_item_type = self.chk.get_generator_yield_type(iter_type, False)
+
+        iter_type_proper = get_proper_type(iter_type)
+
+        if isinstance(iter_type_proper, Instance) and iter_type_proper.args:
+            actual_item_type = iter_type_proper.args[0]
+        else:
+            actual_item_type = self.chk.get_generator_yield_type(iter_type, False)
 
         self.chk.check_subtype(
             actual_item_type,

test-data/unit/check-functions.test

@@ -3768,3 +3768,14 @@ class C:
 
 def defer() -> int:
     return 1
+
+
+[case testYieldFromIteratorMismatch]
+from typing import Generator, Iterator
+
+class A(Iterator[int]):
+    def __next__(self) -> int: ...
+    def __iter__(self) -> "A": ...
+
+def f() -> Generator[tuple[int, ...], None, None]:
+    yield from A()  # E: Incompatible types in "yield"