Handle missing diff_refs attribute

Recently, on a production Zuul acting on projects hosted on gitlab.com,
it has been discovered that a merge requested fetched from the
API (just after Zuul receives the merge request created event) could have
the "diff_refs" attribute set to None.

Related bug: https://gitlab.com/gitlab-org/gitlab/-/issues/386562

Leading to the following stacktrace in the logs:

2022-12-14 10:08:47,921 ERROR zuul.GitlabEventConnector: Exception handling Gitlab event:
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/zuul/driver/gitlab/gitlabconnection.py", line 102, in run
    self.event_queue.election.run(self._run)
  File "/usr/local/lib/python3.8/site-packages/zuul/zk/election.py", line 28, in run
    return super().run(func, *args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/kazoo/recipe/election.py", line 54, in run
    func(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/zuul/driver/gitlab/gitlabconnection.py", line 110, in _run
    self._handleEvent(event)
  File "/usr/local/lib/python3.8/site-packages/zuul/driver/gitlab/gitlabconnection.py", line 246, in _handleEvent
    self.connection._getChange(change_key, refresh=True,
  File "/usr/local/lib/python3.8/site-packages/zuul/driver/gitlab/gitlabconnection.py", line 621, in _getChange
    change = self._change_cache.updateChangeWithRetry(change_key, change,
  File "/usr/local/lib/python3.8/site-packages/zuul/zk/change_cache.py", line 432, in updateChangeWithRetry
    update_func(change)
  File "/usr/local/lib/python3.8/site-packages/zuul/driver/gitlab/gitlabconnection.py", line 619, in _update_change
    self._updateChange(c, event, mr)
  File "/usr/local/lib/python3.8/site-packages/zuul/driver/gitlab/gitlabconnection.py", line 665, in _updateChange
    change.commit_id = change.mr['diff_refs'].get('head_sha')
AttributeError: 'NoneType' object has no attribute 'get'

The attribute "diff_refs" becomes an object (with the expected keys) few
moments later.

In order to avoid this situation, this change adds a mechanism to retry
fetching a MR until it owns some expected fields. In our case only
"diff_refs".

https://docs.gitlab.com/ee/api/merge_requests.html#response

Tests are included with that change.

Change-Id: I6f279516728def655acb8933542a02a4dbb3ccb6

1 files changed, 59 insertions, 2 deletions

diff --git a/tests/unit/test_gitlab_driver.py b/tests/unit/test_gitlab_driver.py
index 6c4d4eeb9..e04a3b5d6 100644
--- a/tests/unit/test_gitlab_driver.py
+++ b/tests/unit/test_gitlab_driver.py
@@ -126,6 +126,27 @@ class TestGitlabDriver(ZuulTestCase):
         self.assertTrue(A.approved)
 
     @simple_layout('layouts/basic-gitlab.yaml', driver='gitlab')
+    def test_merge_request_opened_imcomplete(self):
+
+        now = time.monotonic()
+        complete_at = now + 3
+        with self.fake_gitlab.enable_delayed_complete_mr(complete_at):
+            description = "This is the\nMR description."
+            A = self.fake_gitlab.openFakeMergeRequest(
+                'org/project', 'master', 'A', description=description)
+            self.fake_gitlab.emitEvent(
+                A.getMergeRequestOpenedEvent(), project='org/project')
+            self.waitUntilSettled()
+
+            self.assertEqual('SUCCESS',
+                             self.getJobFromHistory('project-test1').result)
+
+            self.assertEqual('SUCCESS',
+                             self.getJobFromHistory('project-test2').result)
+
+        self.assertTrue(self.fake_gitlab._test_web_server.stats["get_mr"] > 2)
+
+    @simple_layout('layouts/basic-gitlab.yaml', driver='gitlab')
     def test_merge_request_updated(self):
 
         A = self.fake_gitlab.openFakeMergeRequest('org/project', 'master', 'A')
@@ -407,7 +428,7 @@ class TestGitlabDriver(ZuulTestCase):
 
     @simple_layout('layouts/basic-gitlab.yaml', driver='gitlab')
     def test_pull_request_with_dyn_reconf(self):
-
+        path = os.path.join(self.upstream_root, 'org/project')
         zuul_yaml = [
             {'job': {
                 'name': 'project-test3',
@@ -424,11 +445,13 @@ class TestGitlabDriver(ZuulTestCase):
         playbook = "- hosts: all\n  tasks: []"
 
         A = self.fake_gitlab.openFakeMergeRequest(
-            'org/project', 'master', 'A')
+            'org/project', 'master', 'A',
+            base_sha=git.Repo(path).head.object.hexsha)
         A.addCommit(
             {'.zuul.yaml': yaml.dump(zuul_yaml),
              'job.yaml': playbook}
         )
+        A.addCommit({"dummy.file": ""})
         self.fake_gitlab.emitEvent(A.getMergeRequestOpenedEvent())
         self.waitUntilSettled()
 
@@ -440,6 +463,40 @@ class TestGitlabDriver(ZuulTestCase):
                          self.getJobFromHistory('project-test3').result)
 
     @simple_layout('layouts/basic-gitlab.yaml', driver='gitlab')
+    def test_pull_request_with_dyn_reconf_alt(self):
+        with self.fake_gitlab.enable_uncomplete_mr():
+            zuul_yaml = [
+                {'job': {
+                    'name': 'project-test3',
+                    'run': 'job.yaml'
+                }},
+                {'project': {
+                    'check': {
+                        'jobs': [
+                            'project-test3'
+                        ]
+                    }
+                }}
+            ]
+            playbook = "- hosts: all\n  tasks: []"
+            A = self.fake_gitlab.openFakeMergeRequest(
+                'org/project', 'master', 'A')
+            A.addCommit(
+                {'.zuul.yaml': yaml.dump(zuul_yaml),
+                 'job.yaml': playbook}
+            )
+            A.addCommit({"dummy.file": ""})
+            self.fake_gitlab.emitEvent(A.getMergeRequestOpenedEvent())
+            self.waitUntilSettled()
+
+            self.assertEqual('SUCCESS',
+                             self.getJobFromHistory('project-test1').result)
+            self.assertEqual('SUCCESS',
+                             self.getJobFromHistory('project-test2').result)
+            self.assertEqual('SUCCESS',
+                             self.getJobFromHistory('project-test3').result)
+
+    @simple_layout('layouts/basic-gitlab.yaml', driver='gitlab')
     def test_ref_updated_and_tenant_reconfigure(self):
 
         self.waitUntilSettled()