Treat empty yield as no-op for reachability

mypy/checker.py

@@ -132,6 +132,7 @@
     Var,
     WhileStmt,
     WithStmt,
+    YieldExpr,
     is_final_node,
 )
 from mypy.options import Options
@@ -2739,6 +2740,8 @@ def is_noop_for_reachability(self, s: Statement) -> bool:
         elif isinstance(s, ExpressionStmt):
             if isinstance(s.expr, EllipsisExpr):
                 return True
+            elif isinstance(s.expr, YieldExpr) and s.expr.expr is None:
+                return True
             elif isinstance(s.expr, CallExpr):
                 with self.expr_checker.msg.filter_errors():
                     typ = get_proper_type(

test-data/unit/check-unreachable-code.test

@@ -1446,3 +1446,21 @@ def f() -> None:
     Foo()['a'] = 'a'
     x = 0 # This should not be reported as unreachable
 [builtins fixtures/exception.pyi]
+
+[case testIntentionallyEmptyGenerator]
+# flags: --warn-unreachable
+from typing import Generator
+
+def f() -> Generator[None, None, None]:
+    return
+    yield
+
+[case testYieldNoneIgnored]
+# flags: --warn-unreachable
+from typing import Generator
+
+def f() -> Generator[None, None, None]:
+    return
+    yield
+    yield
+    x = 42  # E: Statement is unreachable