galaxy: handle missing 'results' key in cached Galaxy API responses. (#85972)

* galaxy: handle missing 'results' key in cached Galaxy API responses.

* galaxy: clarified AnsibleError message for missing cache results.

* Modified AnsibleError message and added a regression test.

* Fixed formatting issue in test/units/galaxy/test_api.py

* Added a changelog entry.

* Modified changelog.

changelogs/fragments/85918-handle-missing-results.yml

@@ -0,0 +1,6 @@
+---
+bugfixes:
+  - galaxy - previously, some corrupted cache files could cause Ansible Galaxy to fail
+    with a traceback. This has been corrected to display a clear error message explaining
+    how to resolve the problem. 
+    (https://github.com/ansible/ansible/issues/85918)

lib/ansible/galaxy/api.py

@@ -363,7 +363,15 @@ class GalaxyAPI:
                         res['results'].append(result)
 
                 else:
+                    try:
                         res = path_cache['results']
+                    except KeyError as cache_miss_error:
+                        raise AnsibleError(
+                            f"Missing expected 'results' in ansible-galaxy cache: {path_cache!r}. "
+                            "This may indicate cache corruption (for example, from concurrent ansible-galaxy runs) "
+                            "or a bug in how the cache was generated. "
+                            "Try running with --clear-response-cache or --no-cache to work around the issue."
+                        ) from cache_miss_error
 
                 return res
 

test/units/galaxy/test_api.py

@@ -1265,3 +1265,37 @@ def test_clear_cache(cache_dir):
 def test_cache_id(url, expected):
     actual = galaxy_api.get_cache_id(url)
     assert actual == expected
+
+
+def test_cache_missing_results_raises_descriptive_error(mocker):
+    api = GalaxyAPI(None, "test", "https://galaxy.ansible.com/api/")
+
+    mock_cache_entry = {
+        'expires': '2023-01-02T12:00:00Z',
+        'paginated': False
+    }
+
+    api._cache = {'galaxy.ansible.com': {'/api/v1/roles/': mock_cache_entry}}
+
+    mocker.patch('ansible.galaxy.api.urlparse')
+    mocker.patch('ansible.galaxy.api.parse_qs', return_value={})
+    mocker.patch('ansible.galaxy.api.get_cache_id',
+                 return_value='galaxy.ansible.com')
+
+    mock_datetime = mocker.patch('ansible.galaxy.api.datetime')
+
+    mock_comparison = mocker.Mock()
+    mock_comparison.__bool__ = mocker.Mock(return_value=True)
+
+    mock_now = mocker.Mock()
+    mock_expires = mocker.Mock()
+    mock_now.__lt__ = mocker.Mock(return_value=True)
+    mock_datetime.datetime.now.return_value = mock_now
+    mock_datetime.datetime.strptime.return_value = mock_expires
+
+    with pytest.raises(AnsibleError, match="Missing expected 'results' in ansible-galaxy cache"):
+        api._call_galaxy(
+            url='https://galaxy.ansible.com/api/v1/roles/',
+            cache=True,
+            cache_key='/api/v1/roles/'
+        )