Added Repo.merge_base(...) implementation, including test-case.

Fixes #169

Author: Byron

Diff for: doc/source/changes.rst

@@ -2,6 +2,11 @@
 Changelog
 =========
 
+0.3.6 - Features
+================
+* Added `Repo.merge_base()` implementation. See the `respective issue on github <https://github.com/gitpython-developers/GitPython/issues/169>`_
+* A list of all issues can be found here: https://github.com/gitpython-developers/GitPython/issues?q=milestone%3A%22v0.3.6+-+Features%22+
+
 0.3.5 - Bugfixes
 ================
 * push/pull/fetch operations will not block anymore

Diff for: git/repo/base.py

@@ -4,7 +4,11 @@
 # This module is part of GitPython and is released under
 # the BSD License: http://www.opensource.org/licenses/bsd-license.php
 
-from git.exc import InvalidGitRepositoryError, NoSuchPathError
+from git.exc import (
+    InvalidGitRepositoryError,
+    NoSuchPathError,
+    GitCommandError
+)
 from git.cmd import (
     Git,
     handle_process_output
@@ -456,6 +460,36 @@ def iter_commits(self, rev=None, paths='', **kwargs):
 
         return Commit.iter_items(self, rev, paths, **kwargs)
 
+    def merge_base(self, *rev, **kwargs):
+        """Find the closest common ancestor for the given revision (e.g. Commits, Tags, References, etc).
+        :param rev: At least two revs to find the common ancestor for.
+        :param kwargs: Additional arguments to be passed to the repo.git.merge_base() command which does all the work.
+        :return: A list of Commit objects. If --all was not specified as kwarg, the list will have at max one Commit,
+            or is empty if no common merge base exists.
+        :raises ValueError: If not at least two revs are provided
+        """
+        if len(rev) < 2:
+            raise ValueError("Please specify at least two revs, got only %i" % len(rev))
+        # end handle input
+
+        res = list()
+        try:
+            lines = self.git.merge_base(*rev, **kwargs).splitlines()
+        except GitCommandError as err:
+            if err.status == 128:
+                raise
+            # end handle invalid rev
+            # Status code 1 is returned if there is no merge-base
+            # (see https://github.com/git/git/blob/master/builtin/merge-base.c#L16)
+            return res
+        # end exception handling
+
+        for line in lines:
+            res.append(self.commit(line))
+        # end for each merge-base
+
+        return res
+
     def _get_daemon_export(self):
         filename = join(self.git_dir, self.DAEMON_EXPORT_FILE)
         return os.path.exists(filename)

Diff for: git/test/test_repo.py

@@ -27,7 +27,8 @@
     Submodule,
     GitCmdObjectDB,
     Remote,
-    BadName
+    BadName,
+    GitCommandError
 )
 from git.repo.fun import touch
 from git.util import join_path_native
@@ -737,3 +738,24 @@ def test_empty_repo(self, rw_dir):
         # Now a branch should be creatable
         nb = r.create_head('foo')
         assert nb.is_valid()
+
+    def test_merge_base(self):
+        repo = self.rorepo
+        c1 = 'f6aa8d1'
+        c2 = repo.commit('d46e3fe')
+        c3 = '763ef75'
+        self.failUnlessRaises(ValueError, repo.merge_base)
+        self.failUnlessRaises(ValueError, repo.merge_base, 'foo')
+
+        # two commit merge-base
+        res = repo.merge_base(c1, c2)
+        assert isinstance(res, list) and len(res) == 1 and isinstance(res[0], Commit)
+        assert res[0].hexsha.startswith('3936084')
+
+        for kw in ('a', 'all'):
+            res = repo.merge_base(c1, c2, c3, **{kw: True})
+            assert isinstance(res, list) and len(res) == 1
+        # end for eaech keyword signalling all merge-bases to be returned
+
+        # Test for no merge base - can't do as we have
+        self.failUnlessRaises(GitCommandError, repo.merge_base, c1, 'ffffff')