fix(integrations): cache empty repo 409 responses to reduce GitHub API calls (#109153)

Cache the result when GitHub's Git Trees API returns a 409 ("Git
Repository
is empty") instead of re-fetching on every task run.

Previously, when `get_tree` hit a 409 for an empty repo, the exception
propagated without writing to cache. This meant every subsequent
`auto_source_code_config` task run would re-fetch the same empty repos,
wasting API calls and contributing to GitHub rate limiting. For large
orgs
with many empty repos, this adds up to thousands of unnecessary API
calls
per day.

Now we catch `ApiConflictError` in `get_cached_repo_files`, cache an
empty
list with the same TTL as successful results (24h + staggered offset),
and
return early. The existing error handling in `_populate_trees` is
unaffected
since the exception no longer propagates.

Pairs with #109134 which records these 409s as halts instead of failures
in the interaction event lifecycle.

Refs SENTRY-5K7F

Author: trevor-e

src/sentry/integrations/source_code_management/repo_trees.py

@@ -7,7 +7,7 @@
 
 from sentry.integrations.services.integration import RpcOrganizationIntegration
 from sentry.issues.auto_source_code_config.utils.platform import get_supported_extensions
-from sentry.shared_integrations.exceptions import ApiError, IntegrationError
+from sentry.shared_integrations.exceptions import ApiConflictError, ApiError, IntegrationError
 from sentry.utils import metrics
 from sentry.utils.cache import cache
 
@@ -199,7 +199,17 @@ def get_cached_repo_files(
         repo_files: list[str] = cache.get(key, [])
         if use_api:
             # Cache miss – fetch from API
-            tree = self.get_client().get_tree(repo_full_name, tree_sha)
+            try:
+                tree = self.get_client().get_tree(repo_full_name, tree_sha)
+            except ApiConflictError:
+                # Empty repos return 409 — cache the empty result so we don't
+                # keep burning API calls on repos we know have no files.
+                logger.info(
+                    "Caching empty files result for repo",
+                    extra={"repo": repo_full_name},
+                )
+                cache.set(key, [], self.CACHE_SECONDS + shifted_seconds)
+                tree = None
             if tree:
                 # Keep files; discard directories
                 repo_files = [node["path"] for node in tree if node["type"] == "blob"]

tests/sentry/integrations/github/test_integration.py

@@ -899,10 +899,12 @@ def get_installation_helper(self) -> GitHubIntegration:
 
     def _expected_trees(self, repo_info_list=None):
         result = {}
-        # bar and baz are defined to fail, thus, do not show up in the default case
+        # bar (409 empty repo) returns an empty RepoTree since we cache the result
+        # baz (404) still fails and is excluded
         list = repo_info_list or [
             ("xyz", "master", ["src/xyz.py"]),
             ("foo", "master", ["src/sentry/api/endpoints/auth_login.py"]),
+            ("bar", "main", []),
         ]
         for repo, branch, files in list:
             result[f"{self.gh_org}/{repo}"] = RepoTree(
@@ -983,6 +985,7 @@ def test_get_trees_for_org_prevent_exhaustion_some_repos(self) -> None:
                     ("xyz", "master", ["src/xyz.py"]),
                     # Now that the rate limit is reset we should get files for foo
                     ("foo", "master", ["src/sentry/api/endpoints/auth_login.py"]),
+                    ("bar", "main", []),
                 ]
             )
 
@@ -1007,12 +1010,14 @@ def test_get_trees_for_org_rate_limit_401(self) -> None:
         )
 
         # This time the rate limit will not fail, thus, it will fetch the trees
+        # bar (409 empty repo) now returns an empty RepoTree since we cache the empty result
         self.set_rate_limit()
         trees = installation.get_trees_for_org()
         assert trees == self._expected_trees(
             [
                 ("xyz", "master", ["src/xyz.py"]),
                 ("foo", "master", ["src/sentry/api/endpoints/auth_login.py"]),
+                ("bar", "main", []),
             ]
         )
 
@@ -1059,8 +1064,9 @@ def test_get_trees_for_org_makes_API_requests_before_MAX_CONNECTION_ERRORS_is_hi
                     # xyz is missing because its request errors
                     # foo has data because its API request is made in spite of xyz's error
                     ("foo", "master", ["src/sentry/api/endpoints/auth_login.py"]),
-                    # bar and baz are missing because their API requests throw errors for
-                    # other reasons in the default mock responses
+                    # bar (409 empty repo) is present with empty files since we cache the result
+                    # baz (404) is missing because its API request throws an error
+                    ("bar", "main", []),
                 ]
             )