[3.12] gh-110378: Close invalid generators in contextmanager and asynccontextmanager (GH-110499) (#110588)

contextmanager and asynccontextmanager context managers now close an invalid
underlying generator object that yields more then one value.
(cherry picked from commit 96fed66)

Co-authored-by: Serhiy Storchaka <[email protected]>

Author: miss-islington

Lib/contextlib.py

@@ -145,7 +145,10 @@ def __exit__(self, typ, value, traceback):
             except StopIteration:
                 return False
             else:
-                raise RuntimeError("generator didn't stop")
+                try:
+                    raise RuntimeError("generator didn't stop")
+                finally:
+                    self.gen.close()
         else:
             if value is None:
                 # Need to force instantiation so we can reliably
@@ -187,7 +190,10 @@ def __exit__(self, typ, value, traceback):
                     raise
                 exc.__traceback__ = traceback
                 return False
-            raise RuntimeError("generator didn't stop after throw()")
+            try:
+                raise RuntimeError("generator didn't stop after throw()")
+            finally:
+                self.gen.close()
 
 class _AsyncGeneratorContextManager(
     _GeneratorContextManagerBase,
@@ -212,7 +218,10 @@ async def __aexit__(self, typ, value, traceback):
             except StopAsyncIteration:
                 return False
             else:
-                raise RuntimeError("generator didn't stop")
+                try:
+                    raise RuntimeError("generator didn't stop")
+                finally:
+                    await self.gen.aclose()
         else:
             if value is None:
                 # Need to force instantiation so we can reliably
@@ -254,7 +263,10 @@ async def __aexit__(self, typ, value, traceback):
                     raise
                 exc.__traceback__ = traceback
                 return False
-            raise RuntimeError("generator didn't stop after athrow()")
+            try:
+                raise RuntimeError("generator didn't stop after athrow()")
+            finally:
+                await self.gen.aclose()
 
 
 def contextmanager(func):

Lib/test/test_contextlib.py

@@ -157,9 +157,24 @@ def whoo():
                 yield
         ctx = whoo()
         ctx.__enter__()
-        self.assertRaises(
-            RuntimeError, ctx.__exit__, TypeError, TypeError("foo"), None
-        )
+        with self.assertRaises(RuntimeError):
+            ctx.__exit__(TypeError, TypeError("foo"), None)
+        if support.check_impl_detail(cpython=True):
+            # The "gen" attribute is an implementation detail.
+            self.assertFalse(ctx.gen.gi_suspended)
+
+    def test_contextmanager_trap_second_yield(self):
+        @contextmanager
+        def whoo():
+            yield
+            yield
+        ctx = whoo()
+        ctx.__enter__()
+        with self.assertRaises(RuntimeError):
+            ctx.__exit__(None, None, None)
+        if support.check_impl_detail(cpython=True):
+            # The "gen" attribute is an implementation detail.
+            self.assertFalse(ctx.gen.gi_suspended)
 
     def test_contextmanager_except(self):
         state = []

Lib/test/test_contextlib_async.py

@@ -204,6 +204,9 @@ async def whoo():
         await ctx.__aenter__()
         with self.assertRaises(RuntimeError):
             await ctx.__aexit__(TypeError, TypeError('foo'), None)
+        if support.check_impl_detail(cpython=True):
+            # The "gen" attribute is an implementation detail.
+            self.assertFalse(ctx.gen.ag_suspended)
 
     @_async_test
     async def test_contextmanager_trap_no_yield(self):
@@ -225,6 +228,9 @@ async def whoo():
         await ctx.__aenter__()
         with self.assertRaises(RuntimeError):
             await ctx.__aexit__(None, None, None)
+        if support.check_impl_detail(cpython=True):
+            # The "gen" attribute is an implementation detail.
+            self.assertFalse(ctx.gen.ag_suspended)
 
     @_async_test
     async def test_contextmanager_non_normalised(self):

Misc/NEWS.d/next/Library/2023-10-07-13-50-12.gh-issue-110378.Y4L8fl.rst

@@ -0,0 +1,3 @@
+:func:`~contextlib.contextmanager` and
+:func:`~contextlib.asynccontextmanager` context managers now close an invalid
+underlying generator object that yields more then one value.