Merge branch 'jk/p4-locate-branch-point-optim'

"git p4" learned to find branch points more efficiently.

* jk/p4-locate-branch-point-optim:
  git-p4: speed up search for branch parent
  git-p4: ensure complex branches are cloned correctly

Author: gitster

git-p4.py

@@ -3600,19 +3600,18 @@ def importNewBranch(self, branch, maxChange):
         return True
 
     def searchParent(self, parent, branch, target):
-        parentFound = False
-        for blob in read_pipe_lines(["git", "rev-list", "--reverse",
+        targetTree = read_pipe(["git", "rev-parse",
+                                "{}^{{tree}}".format(target)]).strip()
+        for line in read_pipe_lines(["git", "rev-list", "--format=%H %T",
                                      "--no-merges", parent]):
-            blob = blob.strip()
-            if len(read_pipe(["git", "diff-tree", blob, target])) == 0:
-                parentFound = True
+            if line.startswith("commit "):
+                continue
+            commit, tree = line.strip().split(" ")
+            if tree == targetTree:
                 if self.verbose:
-                    print("Found parent of %s in commit %s" % (branch, blob))
-                break
-        if parentFound:
-            return blob
-        else:
-            return None
+                    print("Found parent of %s in commit %s" % (branch, commit))
+                return commit
+        return None
 
     def importChanges(self, changes, origin_revision=0):
         cnt = 1

t/t9801-git-p4-branch.sh

@@ -294,11 +294,13 @@ test_expect_success 'git p4 clone complex branches' '
 		test_path_is_file file3 &&
 		grep update file2 &&
 		git reset --hard p4/depot/branch4 &&
+		git diff-tree --quiet HEAD &&
 		test_path_is_file file1 &&
 		test_path_is_file file2 &&
 		test_path_is_missing file3 &&
 		! grep update file2 &&
 		git reset --hard p4/depot/branch5 &&
+		git diff-tree --quiet HEAD &&
 		test_path_is_file file1 &&
 		test_path_is_file file2 &&
 		test_path_is_file file3 &&