gbp.git.repository: Add a "git merge-base" wrapper

Closes: #672642
Signed-off-by: Guido Günther <agx@sigxcpu.org>

2 files changed, 38 insertions, 0 deletions

diff --git a/gbp/git/repository.py b/gbp/git/repository.py
index 2cc5edae..16bad609 100644
--- a/gbp/git/repository.py
+++ b/gbp/git/repository.py
@@ -299,6 +299,26 @@ class GitRepository(object):
         remote += merge.replace("refs/heads","", 1)
         return remote
 
+    def get_merge_base(self, commit1, commit2):
+        """
+        Get the common ancestor between two commits
+
+        @param commit1: commit SHA1 or name of a branch or tag
+        @type commit1: C{str}
+        @param commit2: commit SHA1 or name of a branch or tag
+        @type commit2: C{str}
+        @return: SHA1 of the common ancestor
+        @rtype: C{str}
+        """
+        args = GitArgs()
+        args.add(commit1)
+        args.add(commit2)
+        sha1, stderr, ret = self._git_inout('merge-base', args.args, capture_stderr=True)
+        if not ret:
+            return sha1.strip()
+        else:
+            raise GitRepositoryError("Failed to get common ancestor: %s" % stderr.strip())
+
     def merge(self, commit, verbose=False, edit=False):
         """
         Merge changes from the named commit into the current branch
diff --git a/tests/test_GitRepository.py b/tests/test_GitRepository.py
index 4367f936..2157d806 100644
--- a/tests/test_GitRepository.py
+++ b/tests/test_GitRepository.py
@@ -631,6 +631,24 @@ def test_update_submodules():
     >>> repo.update_submodules()
     """
 
+def test_get_merge_base():
+    """
+    Find the common ancestor of two objects
+
+    Methods tested:
+        - L{gbp.git.GitRepository.get_merge_bsae}
+
+    >>> import gbp.git
+    >>> repo = gbp.git.GitRepository(repo_dir)
+    >>> sha1 = repo.get_merge_base('master', 'foo')
+    >>> len(sha1)
+    40
+    >>> repo.get_merge_base('master', 'doesnotexist')
+    Traceback (most recent call last):
+    ...
+    GitRepositoryError: Failed to get common ancestor: fatal: Not a valid object name doesnotexist
+    """
+
 def test_teardown():
     """
     Perform the teardown