Fix incorrect type inference for yield from with iterators

mypy/checkexpr.py

@@ -1,6 +1,11 @@
 """Expression type checker. This file is conceptually part of TypeChecker."""
 
 from __future__ import annotations
+<<<<<<< HEAD
+=======
+
+from mypy.types import Instance, get_proper_type
+>>>>>>> d76cb3e76 (Fix iterator element type extraction for yield from)
 
 import enum
 import itertools
@@ -6273,7 +6278,13 @@ 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,

mypy/report.py

@@ -147,7 +147,8 @@ def iterate_python_lines(path: str) -> Iterator[tuple[int, str]]:
     """Return an iterator over (line number, line text) from a Python file."""
     if not os.path.isdir(path):  # can happen with namespace packages
         with tokenize.open(path) as input_file:
-            yield from enumerate(input_file, 1)
+            for item in enumerate(input_file, 1):
+                yield item
 
 
 class FuncCounterVisitor(TraverserVisitor):

test-data/unit/check-functions.test

@@ -3768,3 +3768,14 @@ class C:
 
 def defer() -> int:
     return 1
+
+
+[case testYieldFromIteratorMismatch]
+from typing import Generator, Iterator,Tuple
+
+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"