Fix ansible-test merge change detection.

(cherry picked from commit aa7fe919d3)

test/runner/lib/changes.py

@@ -106,17 +106,10 @@ class ShippableChanges(object):
             display.warning('Unable to find project. Cannot determine changes. All tests will be executed.')
             return None
 
-        merge_runs = sorted(merge_runs, key=lambda r: r['createdAt'])
-        known_commits = set()
-        last_successful_commit = None
-
-        for merge_run in merge_runs:
-            commit_sha = merge_run['commitSha']
-            if commit_sha not in known_commits:
-                known_commits.add(commit_sha)
-                if merge_run['statusCode'] == 30:
-                    if git.is_valid_ref(commit_sha):
-                        last_successful_commit = commit_sha
+        successful_commits = set(run['commitSha'] for run in merge_runs if run['statusCode'] == 30)
+        commit_history = git.get_rev_list(max_count=100)
+        ordered_successful_commits = [commit for commit in commit_history if commit in successful_commits]
+        last_successful_commit = ordered_successful_commits[0] if ordered_successful_commits else None
 
         if last_successful_commit is None:
             display.warning('No successful commit found. All tests will be executed.')

test/runner/lib/git.py

@@ -59,6 +59,24 @@ class Git(object):
         cmd = ['symbolic-ref', '--short', 'HEAD']
         return self.run_git(cmd).strip()
 
+    def get_rev_list(self, commits=None, max_count=None):
+        """
+        :type commits: list[str] | None
+        :type max_count: int | None
+        :rtype: list[str]
+        """
+        cmd = ['rev-list']
+
+        if commits:
+            cmd += commits
+        else:
+            cmd += ['HEAD']
+
+        if max_count:
+            cmd += ['--max-count', '%s' % max_count]
+
+        return self.run_git_split(cmd)
+
     def get_branch_fork_point(self, branch):
         """
         :type branch: str