[PATCH/RFC 1/2] git-p4: Search for parent commit on branch creation

[Vitor Antunes <vitor.hda@gmail.com>]

The new commit is applied sequentially to each blob of the parent branch. The
first blob which results in a zero diff with the new commit is considered the
parent commit. If none is found, then the commit is applied to the top of the
parent branch.
This algorithm requires a checkpoint and a time.sleep() to be able to use
diff-tree, making it slower than what would be desirable. It also requires using
--force argument of fast-import, leaving lots of trash commits when finished.

Signed-off-by: Vitor Antunes <vitor.hda@gmail.com>
---
 contrib/fast-import/git-p4 |   22 ++++++++++++++++++++--
 1 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/contrib/fast-import/git-p4 b/contrib/fast-import/git-p4
index f622a38..0bced6d 100755
--- a/contrib/fast-import/git-p4
+++ b/contrib/fast-import/git-p4
@@ -1671,7 +1671,25 @@ class P4Sync(Command, P4UserMap):
                             parent = self.initialParents[branch]
                             del self.initialParents[branch]
 
-                        self.commit(description, filesForCommit, branch, [branchPrefix], parent)
+                        parentFound = 0
+                        if len(parent) > 0:
+                            self.gitStream.write("checkpoint\n\n")
+                            time.sleep(0.1)
+                            for blob in read_pipe_lines("git rev-list --reverse --no-merges %s" % parent):
+                                blob = blob.strip()
+                                self.gitStream.write("reset %s\nfrom %s\n" % (branch, blob))
+                                self.commit(description, filesForCommit, branch, [branchPrefix], blob)
+                                self.gitStream.write("checkpoint\n\n")
+                                time.sleep(0.1)
+                                if len( read_pipe("git diff-tree %s %s" % (blob, branch)) ) == 0:
+                                    parentFound = 1
+                                    if self.verbose:
+                                        print "Found parent of %s in commit %s" % (branch, blob)
+                                    break
+                        if not parentFound:
+                            if self.verbose:
+                                print "Parent of %s not found. Committing into head of %s" % (branch, parent)
+                            self.commit(description, filesForCommit, branch, [branchPrefix], parent)
                 else:
                     files = self.extractFilesFromCommit(description)
                     self.commit(description, files, self.branch, self.depotPaths,
@@ -1948,7 +1966,7 @@ class P4Sync(Command, P4UserMap):
 
         self.tz = "%+03d%02d" % (- time.timezone / 3600, ((- time.timezone % 3600) / 60))
 
-        importProcess = subprocess.Popen(["git", "fast-import"],
+        importProcess = subprocess.Popen(["git", "fast-import", "--force"],
                                          stdin=subprocess.PIPE, stdout=subprocess.PIPE,
                                          stderr=subprocess.PIPE);
         self.gitOutput = importProcess.stdout
-- 
1.7.5.4