Fix use of removed --preserve-merges option

The --preserve-merges (-p) option was replaced by --rebase-merges (-r).
This fixes the following error when using git version 2.34.0:

    Errors running git rebase -p -i remotes/gerrit/stable/xena
    fatal: --preserve-merges was replaced by --rebase-merges

In order to keep compatibility with git < 2.18.0 we detect the git
version and use the old --preserve-merges flag when the version is older
than 2.18.0.

Co-Authored-By: Clark Boylan <clark.boylan@gmail.com>
Change-Id: I04de3d0f20aa6bafcf746b7706d61dd9b9af296c

2 files changed, 38 insertions, 14 deletions

diff --git a/git_review/cmd.py b/git_review/cmd.py
index 16b613a..9215b5d 100644
--- a/git_review/cmd.py
+++ b/git_review/cmd.py
@@ -909,10 +909,25 @@ def rebase_changes(branch, remote, interactive=True):
                   "re-run with the '-R' option enabled." % (branch, remote))
         sys.exit(1)
 
-    if interactive:
-        cmd = "git rebase -p -i %s" % remote_branch
-    else:
-        cmd = "git rebase -p %s" % remote_branch
+    # Determine git version to set rebase flags below.
+    output = run_command("git version")
+    rebase_flag = "--rebase-merges"
+    if "git version" in output:
+        try:
+            v = output.rsplit(None, 1)[1]
+            gitv = tuple(map(int, v.split('.')[:3]))
+            if gitv < (2, 18, 0):
+                rebase_flag = "--preserve-merges"
+        except Exception:
+            # We tried to determine the version and failed. Use current git
+            # flag as fallback.
+            warn("Could not determine git version. "
+                 "Using modern git rebase flags.")
+
+    interactive_flag = interactive and '-i' or ''
+
+    cmd = "git rebase %s %s %s" % \
+        (rebase_flag, interactive_flag, remote_branch)
 
     (status, output) = run_command_status(cmd, GIT_EDITOR='true')
     if status != 0:
diff --git a/git_review/tests/test_git_review.py b/git_review/tests/test_git_review.py
index 4717bdd..dcb9232 100644
--- a/git_review/tests/test_git_review.py
+++ b/git_review/tests/test_git_review.py
@@ -323,9 +323,11 @@ class GitReviewTestCase(tests.BaseGitReviewTestCase):
                             'create conflict with master')
 
         exc = self.assertRaises(Exception, self._run_git_review)
-        self.assertIn(
-            "Errors running git rebase -p -i remotes/%s/master" % self._remote,
-            exc.args[0])
+        rebased = ("Errors running git rebase --rebase-merges "
+                   "-i remotes/%s/master" % self._remote in exc.args[0] or
+                   "Errors running git rebase --preserve-merges "
+                   "-i remotes/%s/master" % self._remote in exc.args[0])
+        self.assertTrue(rebased)
         self.assertIn("It is likely that your change has a merge conflict.",
                       exc.args[0])
 
@@ -341,9 +343,11 @@ class GitReviewTestCase(tests.BaseGitReviewTestCase):
                             self._dir('test', 'new_test_file.txt'))
 
         review_res = self._run_git_review('-v')
-        self.assertIn(
-            "Running: git rebase -p -i remotes/%s/master" % self._remote,
-            review_res)
+        rebased = ("Running: git rebase --rebase-merges "
+                   "-i remotes/%s/master" % self._remote in review_res or
+                   "Running: git rebase --preserve-merges "
+                   "-i remotes/%s/master" % self._remote in review_res)
+        self.assertTrue(rebased)
         self.assertEqual(self._run_git('rev-parse', 'HEAD^1'), head_1)
 
     def test_uploads_with_nondefault_rebase(self):
@@ -383,8 +387,10 @@ class GitReviewTestCase(tests.BaseGitReviewTestCase):
 
         review_res = self._run_git_review('-v')
         # no rebase needed; if it breaks it would try to rebase to master
-        self.assertNotIn("Running: git rebase -p -i remotes/origin/master",
-                         review_res)
+        self.assertNotIn("Running: git rebase --rebase-merges "
+                         "-i remotes/origin/master", review_res)
+        self.assertNotIn("Running: git rebase --preserve-merges "
+                         "-i remotes/origin/master", review_res)
         # Don't need to query gerrit for the branch as the second half
         # of this test will work only if the branch was correctly
         # stored in gerrit
@@ -401,8 +407,11 @@ class GitReviewTestCase(tests.BaseGitReviewTestCase):
         self.assertEqual(change_id, new_change_id)
         review_res = self._run_git_review('-v')
         # caused the right thing to happen
-        self.assertIn("Running: git rebase -p -i remotes/origin/maint",
-                      review_res)
+        rebased = ("Running: git rebase --rebase-merges "
+                   "-i remotes/origin/maint" in review_res or
+                   "Running: git rebase --preserve-merges "
+                   "-i remotes/origin/maint" in review_res)
+        self.assertTrue(rebased)
 
         # track different branch than expected in changeset
         branch = self._run_git('rev-parse', '--abbrev-ref', 'HEAD')