[StGit PATCH 1/2] Do simple in-index merge with diff+apply instead of read-tree

["Karl Hasselström" <kha@treskal.com>]

The advantage is that patch application will resolve some file content
conflicts for us, so that we'll fall back to merge-recursive less
often. This is a significant speedup, especially since merge-recursive
needs to touch the worktree, which means we have to check out the
index first.

(A simple test, pushing 250 patches in a 32k-file repository, with one
file-level merge necessary per push, went from 1.07 to 0.36 seconds
per patch with this patch applied.)

Signed-off-by: Karl Hasselström <kha@treskal.com>

---

 stgit/lib/git.py |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)


diff --git a/stgit/lib/git.py b/stgit/lib/git.py
index 6ccdfa7..a38eaa5 100644
--- a/stgit/lib/git.py
+++ b/stgit/lib/git.py
@@ -475,9 +475,10 @@ class Repository(RunWithEnv):
             return ours
 
         index = self.temp_index()
+        index.read_tree(ours)
         try:
-            index.merge(base, ours, theirs)
             try:
+                index.apply_treediff(base, theirs)
                 return index.write_tree()
             except MergeException:
                 return None
@@ -548,10 +549,6 @@ class Index(RunWithEnv):
             return False
         else:
             return True
-    def merge(self, base, ours, theirs):
-        """In-index merge, no worktree involved."""
-        self.run(['git', 'read-tree', '-m', '-i', '--aggressive',
-                  base.sha1, ours.sha1, theirs.sha1]).no_output()
     def apply(self, patch_text):
         """In-index patch application, no worktree involved."""
         try:
@@ -559,6 +556,12 @@ class Index(RunWithEnv):
                      ).raw_input(patch_text).no_output()
         except run.RunException:
             raise MergeException('Patch does not apply cleanly')
+    def apply_treediff(self, tree1, tree2):
+        """Apply the diff from C{tree1} to C{tree2} to the index."""
+        # Passing --full-index here is necessary to support binary
+        # files. It is also sufficient, since the repository already
+        # contains all involved objects.
+        self.apply(self.__repository.diff_tree(tree1, tree2, ['--full-index']))
     def delete(self):
         if os.path.isfile(self.__filename):
             os.remove(self.__filename)