fix: wrapping context __exit__ leak (#13626)

We fix a leak in the universal wrapping context caused to bound __exit__
method leaking in CPython 3.9 and 3.10. This was due to a reference to
the bound method __exit__ of the universal wrapping context not getting
popped from the stack before every return statement. Every call to a
wrapped function would then create one such bounded method object that
would not get GC'd. No other versions of CPython are affected because
the bytecode and/or approach are different.

## Checklist
- [ ] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Author: P403n1x87

ddtrace/internal/wrapping/context.py

@@ -230,11 +230,14 @@
 
     CONTEXT_RETURN.parse(
         r"""
+            pop_block
             load_const                  {context}
             load_method                 $__return__
             rot_three
             rot_three
             call_method                 1
+            rot_two
+            pop_top
         """
     )
 
@@ -258,11 +261,14 @@
 
     CONTEXT_RETURN.parse(
         r"""
+            pop_block
             load_const                  {context}
             load_method                 $__return__
             rot_three
             rot_three
             call_method                 1
+            rot_two
+            pop_top
         """
     )
 

releasenotes/notes/fix-wrapping-context-memory-leak-ad3d8f27586ba662.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    code origin: fixed a potential memory leak when collecting entry span
+    location information.

tests/internal/test_wrapping.py

@@ -1,5 +1,6 @@
 import asyncio
 from contextlib import asynccontextmanager
+import gc
 import inspect
 import sys
 from types import CoroutineType
@@ -805,3 +806,21 @@ async def fibonacci(n):
     await asyncio.gather(*[fibonacci(n) for n in range(1, N)])
 
     assert set(values) == {(n, n) for n in range(0, N)}
+
+
+def test_wrapping_context_method_leaks():
+    def foo():
+        return 42
+
+    wc = DummyWrappingContext(foo)
+    wc.wrap()
+
+    method_count = len([_ for _ in gc.get_objects() if type(_).__name__ == "method"])
+
+    for _ in range(10000):
+        foo()
+
+    gc.collect()
+
+    new_method_count = len([_ for _ in gc.get_objects() if type(_).__name__ == "method"])
+    assert new_method_count <= method_count + 1