fix: avoid retaining routing parameter instances in cache (#17961)

functools.cache keeps method arguments, including self, in its unbounded
cache. As a result, RoutingParameter instances remain alive after
routing resolution.

Use the existing instance-scoped utils.cached_property for the compiled
regex and routing key while preserving the to_regex() method API. Add a
regression test that verifies a populated cache does not retain the
instance.

Testing:
- pytest
packages/gapic-generator/tests/unit/schema/wrappers/test_routing.py -q
(Python 3.10 and 3.14)
- pytest packages/gapic-generator/tests/unit/schema/wrappers -q (Python
3.14)

Author: mingi3314

packages/gapic-generator/gapic/schema/wrappers.py

@@ -30,7 +30,6 @@
 import collections
 import copy
 import dataclasses
-import functools
 import json
 import keyword
 import re
@@ -1289,14 +1288,14 @@ def _to_regex(self, path_template: str) -> Pattern:
         """
         return re.compile(f"^{self._convert_to_regex(path_template)}$")
 
-    # Use caching to avoid repeated computation
-    @functools.cache
-    def to_regex(self) -> Pattern:
+    @utils.cached_property
+    def _regex(self) -> Pattern:
         return self._to_regex(self.path_template)
 
-    @property
-    # Use caching to avoid repeated computation
-    @functools.cache
+    def to_regex(self) -> Pattern:
+        return self._regex
+
+    @utils.cached_property
     def key(self) -> Union[str, None]:
         if self.path_template == "":
             return self.field

packages/gapic-generator/tests/unit/schema/wrappers/test_routing.py

@@ -14,7 +14,10 @@
 
 from gapic.schema import wrappers
 
+import gc
 import json
+import uuid
+import weakref
 import proto
 import pytest
 
@@ -146,6 +149,21 @@ def test_routing_parameter_key(field, path_template, expected):
     assert param.key == expected
 
 
+def test_routing_parameter_cache_does_not_retain_instance():
+    unique_id = f"id_{uuid.uuid4().hex}"
+    param = wrappers.RoutingParameter(
+        f"table_name_{unique_id}", f"{{{unique_id}=projects/*}}/instances/*/**"
+    )
+    _ = param.to_regex()
+    _ = param.key
+    param_ref = weakref.ref(param)
+
+    del param
+    gc.collect()
+
+    assert param_ref() is None
+
+
 def test_routing_parameter_multi_segment_raises():
     param = wrappers.RoutingParameter(
         "table_name", "{project_id=projects/*}/{instance_id=instances/*}/*/**"