Repository: allow passing a favor option to merge_commits

I've gone with taking a string and converting it because the depth of
the namespacing in the libgit2 name is rather large and we don't care
about the global namespace that C has; and this also lets us pass the
same as the '-X' option to git-merge.

pygit2/decl.h

@@ -598,7 +598,12 @@ void git_blame_free(git_blame *blame);
 
 typedef enum { ... } git_merge_tree_flag_t;
 
-typedef enum { ... } git_merge_file_favor_t;
+typedef enum {
+	GIT_MERGE_FILE_FAVOR_NORMAL = 0,
+	GIT_MERGE_FILE_FAVOR_OURS = 1,
+	GIT_MERGE_FILE_FAVOR_THEIRS = 2,
+	GIT_MERGE_FILE_FAVOR_UNION = 3,
+} git_merge_file_favor_t;
 
 typedef struct {
 	unsigned int version;
@@ -609,5 +614,7 @@ typedef struct {
 	git_merge_file_favor_t file_favor;
 } git_merge_options;
 
+#define GIT_MERGE_OPTIONS_VERSION ...
 
+int git_merge_init_options(git_merge_options *opts,	unsigned int version);
 int git_merge_commits(git_index **out, git_repository *repo, const git_commit *our_commit, const git_commit *their_commit, const git_merge_options *opts);

pygit2/repository.py

@@ -510,7 +510,7 @@ class Repository(_Repository):
     #
     # Merging
     #
-    def merge_commits(self, ours, theirs):
+    def merge_commits(self, ours, theirs, favor='normal'):
         """Merge two arbitrary commits
 
         Arguments:
@@ -519,16 +519,37 @@ class Repository(_Repository):
             The commit to take as "ours" or base.
         theirs
             The commit which will be merged into "ours"
+        favor
+            How to deal with file-level conflicts. Can be one of
 
-        Both can be any object which peels to a commit or the id
+            * normal (default). Conflicts will be preserved.
+            * ours. The "ours" side of the conflict region is used.
+            * theirs. The "theirs" side of the conflict region is used.
+            * union. Unique lines from each side will be used.
+
+            for all but NORMAL, the index will not record a conflict.
+
+        Both "ours" and "theirs" can be any object which peels to a commit or the id
         (string or Oid) of an object which peels to a commit.
 
         Returns an index with the result of the merge
 
         """
+        def favor_to_enum(favor):
+            if favor == 'normal':
+                return C.GIT_MERGE_FILE_FAVOR_NORMAL
+            elif favor == 'ours':
+                return C.GIT_MERGE_FILE_FAVOR_OURS
+            elif favor == 'theirs':
+                return C.GIT_MERGE_FILE_FAVOR_THEIRS
+            elif favor == 'union':
+                return C.GIT_MERGE_FILE_FAVOR_UNION
+            else:
+                return None
 
         ours_ptr = ffi.new('git_commit **')
         theirs_ptr = ffi.new('git_commit **')
+        opts = ffi.new('git_merge_options *')
         cindex = ffi.new('git_index **')
 
         if is_string(ours) or isinstance(ours, Oid):
@@ -539,10 +560,19 @@ class Repository(_Repository):
         ours = ours.peel(Commit)
         theirs = theirs.peel(Commit)
 
+        err = C.git_merge_init_options(opts, C.GIT_MERGE_OPTIONS_VERSION)
+        check_error(err)
+
+        favor_val = favor_to_enum(favor)
+        if favor_val is None:
+            raise ValueError("unkown favor value %s" % favor)
+
+        opts.file_favor = favor_val
+
         ffi.buffer(ours_ptr)[:] = ours._pointer[:]
         ffi.buffer(theirs_ptr)[:] = theirs._pointer[:]
 
-        err = C.git_merge_commits(cindex, self._repo, ours_ptr[0], theirs_ptr[0], ffi.NULL)
+        err = C.git_merge_commits(cindex, self._repo, ours_ptr[0], theirs_ptr[0], opts)
         check_error(err)
 
         return Index.from_c(self, cindex)

test/test_merge.py

@@ -158,3 +158,10 @@ class MergeCommitsTest(utils.RepoTestCaseForMerging):
         merge_tree = index.write_tree()
 
         self.assertEqual(merge_tree, merge_commits_tree)
+
+    def test_merge_commits_favor(self):
+        branch_head_hex = '1b2bae55ac95a4be3f8983b86cd579226d0eb247'
+        merge_index = self.repo.merge_commits(self.repo.head.target, branch_head_hex, favor='ours')
+        self.assertTrue(merge_index.conflicts is None)
+
+        self.assertRaises(ValueError, self.repo.merge_commits, self.repo.head.target, branch_head_hex, favor='foo')