Merge "Add rebase-merge merge mode"

8 files changed, 132 insertions, 16 deletions

diff --git a/doc/source/config/project.rst b/doc/source/config/project.rst
index af3faa943..04d61b5d3 100644
--- a/doc/source/config/project.rst
+++ b/doc/source/config/project.rst
@@ -138,13 +138,20 @@ pipeline.
       .. value:: cherry-pick
 
          Cherry-picks each change onto the branch rather than
-         performing any merges. This is not supported by Github and GitLab.
+         performing any merges. This is not supported by GitHub and GitLab.
 
       .. value:: squash-merge
 
          Squash merges each change onto the branch. This maps to the
          merge mode ``squash`` in GitHub and GitLab.
 
+      .. value:: rebase
+
+         Rebases the changes onto the branch.  This is only supported
+         by GitHub and maps to the ``rebase`` merge mode (but
+         does not alter committer information in the way that GitHub
+         does in the repos that Zuul prepares for jobs).
+
    .. attr:: vars
       :default: None
 
diff --git a/releasenotes/notes/rebase-merge-6b96aa541cd53492.yaml b/releasenotes/notes/rebase-merge-6b96aa541cd53492.yaml
new file mode 100644
index 000000000..02f87c389
--- /dev/null
+++ b/releasenotes/notes/rebase-merge-6b96aa541cd53492.yaml
@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    The :value:`project.merge-mode.rebase` merge-mode is now supported
+    for GitHub.
diff --git a/tests/fixtures/layouts/gate-github-rebase.yaml b/tests/fixtures/layouts/gate-github-rebase.yaml
new file mode 100644
index 000000000..80408decd
--- /dev/null
+++ b/tests/fixtures/layouts/gate-github-rebase.yaml
@@ -0,0 +1,38 @@
+- pipeline:
+    name: gate
+    manager: dependent
+    trigger:
+      github:
+        - event: pull_request
+          action:
+            - opened
+            - changed
+            - reopened
+          branch: ^master$
+    success:
+      github:
+        status: success
+        merge: true
+    failure:
+      github: {}
+
+- job:
+    name: base
+    parent: null
+    run: playbooks/base.yaml
+
+- job:
+    name: project-test1
+    run: playbooks/project-test1.yaml
+
+- job:
+    name: project-test2
+    run: playbooks/project-test2.yaml
+
+- project:
+    name: org/project
+    merge-mode: rebase
+    gate:
+      jobs:
+        - project-test1
+        - project-test2
diff --git a/tests/unit/test_github_driver.py b/tests/unit/test_github_driver.py
index 49dae0ccb..90d69a7bc 100644
--- a/tests/unit/test_github_driver.py
+++ b/tests/unit/test_github_driver.py
@@ -1356,11 +1356,59 @@ class TestGithubDriver(ZuulTestCase):
         self.assertEquals(A.comments[1],
                           'Merge mode cherry-pick not supported by Github')
 
+    @simple_layout('layouts/gate-github-rebase.yaml', driver='github')
+    def test_merge_method_rebase(self):
+        """
+        Tests that the merge mode gets forwarded to the reporter and the
+        PR was rebased.
+        """
+        self.executor_server.keep_jobdir = True
+        self.executor_server.hold_jobs_in_build = True
+        github = self.fake_github.getGithubClient()
+        repo = github.repo_from_project('org/project')
+        repo._set_branch_protection(
+            'master', contexts=['tenant-one/check', 'tenant-one/gate'])
+
+        A = self.fake_github.openFakePullRequest('org/project', 'master', 'A')
+        repo.create_status(A.head_sha, 'success', 'example.com', 'description',
+                           'tenant-one/check')
+
+        # Create a second commit on master to verify rebase behavior
+        self.create_commit('org/project', message="Test rebase commit")
+
+        self.fake_github.emitEvent(A.getPullRequestOpenedEvent())
+        self.waitUntilSettled()
+
+        build = self.builds[-1]
+        path = os.path.join(build.jobdir.src_root, 'github.com/org/project')
+        repo = git.Repo(path)
+        repo_messages = [c.message.strip() for c in repo.iter_commits()]
+        repo_messages.reverse()
+        expected = [
+            'initial commit',
+            'initial commit',  # simple_layout adds a second "initial commit"
+            'Test rebase commit',
+            'A-1',
+        ]
+        self.assertEqual(expected, repo_messages)
+
+        self.executor_server.hold_jobs_in_build = False
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+        # the change should have entered the gate
+        self.assertEqual(2, len(self.history))
+
+        # now check if the merge was done via rebase
+        merges = [report for report in self.fake_github.github_data.reports
+                  if report[2] == 'merge']
+        assert (len(merges) == 1 and merges[0][3] == 'rebase')
+
     @simple_layout('layouts/gate-github-squash-merge.yaml', driver='github')
     def test_merge_method_squash_merge(self):
         """
         Tests that the merge mode gets forwarded to the reporter and the
-        merge fails because cherry-pick is not supported by github.
+        PR was squashed.
         """
         github = self.fake_github.getGithubClient()
         repo = github.repo_from_project('org/project')
@@ -1381,7 +1429,7 @@ class TestGithubDriver(ZuulTestCase):
         # the change should have entered the gate
         self.assertEqual(2, len(self.history))
 
-        # now check if the merge was done via rebase
+        # now check if the merge was done via squash
         merges = [report for report in self.fake_github.github_data.reports
                   if report[2] == 'merge']
         assert (len(merges) == 1 and merges[0][3] == 'squash')
diff --git a/zuul/configloader.py b/zuul/configloader.py
index 63633a54c..03953eb31 100644
--- a/zuul/configloader.py
+++ b/zuul/configloader.py
@@ -1113,7 +1113,8 @@ class ProjectParser(object):
             'vars': ansible_vars_dict,
             'templates': [str],
             'merge-mode': vs.Any('merge', 'merge-resolve',
-                                 'cherry-pick', 'squash-merge'),
+                                 'cherry-pick', 'squash-merge',
+                                 'rebase'),
             'default-branch': str,
             'queue': str,
             str: pipeline_contents,
diff --git a/zuul/driver/github/githubreporter.py b/zuul/driver/github/githubreporter.py
index 8c5e8944c..e5c5ebfbd 100644
--- a/zuul/driver/github/githubreporter.py
+++ b/zuul/driver/github/githubreporter.py
@@ -17,9 +17,8 @@ import logging
 import voluptuous as v
 import time
 
+from zuul import model
 from zuul.lib.logutil import get_annotated_logger
-from zuul.model import MERGER_MERGE_RESOLVE, MERGER_MERGE, MERGER_MAP, \
-    MERGER_SQUASH_MERGE
 from zuul.reporter import BaseReporter
 from zuul.exceptions import MergeFailure
 from zuul.driver.util import scalar_or_list
@@ -34,9 +33,10 @@ class GithubReporter(BaseReporter):
 
     # Merge modes supported by github
     merge_modes = {
-        MERGER_MERGE: 'merge',
-        MERGER_MERGE_RESOLVE: 'merge',
-        MERGER_SQUASH_MERGE: 'squash',
+        model.MERGER_MERGE: 'merge',
+        model.MERGER_MERGE_RESOLVE: 'merge',
+        model.MERGER_SQUASH_MERGE: 'squash',
+        model.MERGER_REBASE: 'rebase',
     }
 
     def __init__(self, driver, connection, pipeline, config=None):
@@ -189,7 +189,8 @@ class GithubReporter(BaseReporter):
         merge_mode = item.current_build_set.getMergeMode()
 
         if merge_mode not in self.merge_modes:
-            mode = [x[0] for x in MERGER_MAP.items() if x[1] == merge_mode][0]
+            mode = [x[0] for x in model.MERGER_MAP.items()
+                    if x[1] == merge_mode][0]
             self.log.warning('Merge mode %s not supported by Github', mode)
             raise MergeFailure('Merge mode %s not supported by Github' % mode)
 
diff --git a/zuul/merger/merger.py b/zuul/merger/merger.py
index 34b495fcc..09968eac6 100644
--- a/zuul/merger/merger.py
+++ b/zuul/merger/merger.py
@@ -582,7 +582,7 @@ class Repo(object):
         repo.git.merge(*args)
         return repo.head.commit
 
-    def squash_merge(self, item, zuul_event_id=None):
+    def squashMerge(self, item, zuul_event_id=None):
         log = get_annotated_logger(self.log, zuul_event_id)
         repo = self.createRepoObject(zuul_event_id)
         args = ['--squash', 'FETCH_HEAD']
@@ -594,6 +594,17 @@ class Repo(object):
             'Merge change %s,%s' % (item['number'], item['patchset']))
         return repo.head.commit
 
+    def rebaseMerge(self, item, base, zuul_event_id=None):
+        log = get_annotated_logger(self.log, zuul_event_id)
+        repo = self.createRepoObject(zuul_event_id)
+        args = [base]
+        ref = item['ref']
+        self.fetch(ref, zuul_event_id=zuul_event_id)
+        log.debug("Rebasing %s with args %s", ref, args)
+        repo.git.checkout('FETCH_HEAD')
+        repo.git.rebase(*args)
+        return repo.head.commit
+
     def fetch(self, ref, zuul_event_id=None):
         repo = self.createRepoObject(zuul_event_id)
         # NOTE: The following is currently not applicable, but if we
@@ -1029,14 +1040,14 @@ class Merger(object):
             for message in messages:
                 ref_log.debug(message)
 
-    def _mergeChange(self, item, ref, zuul_event_id):
+    def _mergeChange(self, item, base, zuul_event_id):
         log = get_annotated_logger(self.log, zuul_event_id)
         repo = self.getRepo(item['connection'], item['project'],
                             zuul_event_id=zuul_event_id)
         try:
-            repo.checkout(ref, zuul_event_id=zuul_event_id)
+            repo.checkout(base, zuul_event_id=zuul_event_id)
         except Exception:
-            log.exception("Unable to checkout %s", ref)
+            log.exception("Unable to checkout %s", base)
             return None, None
 
         try:
@@ -1050,8 +1061,11 @@ class Merger(object):
                 commit = repo.cherryPick(item['ref'],
                                          zuul_event_id=zuul_event_id)
             elif mode == zuul.model.MERGER_SQUASH_MERGE:
-                commit = repo.squash_merge(
+                commit = repo.squashMerge(
                     item, zuul_event_id=zuul_event_id)
+            elif mode == zuul.model.MERGER_REBASE:
+                commit = repo.rebaseMerge(
+                    item, base, zuul_event_id=zuul_event_id)
             else:
                 raise Exception("Unsupported merge mode: %s" % mode)
         except git.GitCommandError:
diff --git a/zuul/model.py b/zuul/model.py
index 7269dee24..100785885 100644
--- a/zuul/model.py
+++ b/zuul/model.py
@@ -55,13 +55,15 @@ from zuul.zk.components import COMPONENT_REGISTRY
 MERGER_MERGE = 1          # "git merge"
 MERGER_MERGE_RESOLVE = 2  # "git merge -s resolve"
 MERGER_CHERRY_PICK = 3    # "git cherry-pick"
-MERGER_SQUASH_MERGE = 4    # "git merge --squash"
+MERGER_SQUASH_MERGE = 4   # "git merge --squash"
+MERGER_REBASE = 5         # "git rebase"
 
 MERGER_MAP = {
     'merge': MERGER_MERGE,
     'merge-resolve': MERGER_MERGE_RESOLVE,
     'cherry-pick': MERGER_CHERRY_PICK,
     'squash-merge': MERGER_SQUASH_MERGE,
+    'rebase': MERGER_REBASE,
 }
 
 PRECEDENCE_NORMAL = 0