[PATCH v2 2/3] git-p4: Search for parent commit on branch creation

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

To find out which is its parent the commit of the new branch is applied
sequentially to each blob of the parent branch from the newest to the
oldest. The first blob which results in a zero diff is considered the
parent commit. If none is found, then the commit is applied to the top
of the parent branch.

A fast-import "checkpoint" call is required for each comparison because
diff-tree is only able to work with blobs on disk. But most of these
commits will not be part of the final imported tree, making fast-import
fail. To avoid this, the temporary branches are tracked and then removed
at the end of the import process.

Signed-off-by: Vitor Antunes <vitor.hda@gmail.com>
---
 contrib/fast-import/git-p4 |   30 +++++++++++++++++++++++++++++-
 1 files changed, 29 insertions(+), 1 deletions(-)

diff --git a/contrib/fast-import/git-p4 b/contrib/fast-import/git-p4
index 417d119..2e3b741 100755
--- a/contrib/fast-import/git-p4
+++ b/contrib/fast-import/git-p4
@@ -1429,6 +1429,8 @@ class P4Sync(Command, P4UserMap):
         self.cloneExclude = []
         self.useClientSpec = False
         self.clientSpecDirs = None
+        self.tempBranches = []
+        self.tempBranchLocation = "git-p4-tmp"
 
         if gitConfig("git-p4.syncFromOrigin") == "false":
             self.syncWithOrigin = False
@@ -2012,7 +2014,27 @@ class P4Sync(Command, P4UserMap):
                             parent = self.initialParents[branch]
                             del self.initialParents[branch]
 
-                        self.commit(description, filesForCommit, branch, [branchPrefix], parent)
+                        parentFound = False
+                        if len(parent) > 0:
+                            tempBranch = os.path.join(self.tempBranchLocation, "%d" % (change))
+                            if self.verbose:
+                                print "Creating temporary branch: " + tempBranch
+                            self.commit(description, filesForCommit, tempBranch, [branchPrefix])
+                            self.tempBranches.append(tempBranch)
+                            self.checkpoint()
+                            for blob in read_pipe_lines("git rev-list --reverse --no-merges %s" % parent):
+                                blob = blob.strip()
+                                if len( read_pipe("git diff-tree %s %s" % (blob, tempBranch)) ) == 0:
+                                    parentFound = True
+                                    if self.verbose:
+                                        print "Found parent of %s in commit %s" % (branch, blob)
+                                    break
+                        if parentFound:
+                            self.commit(description, filesForCommit, branch, [branchPrefix], blob)
+                        else:
+                            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,
@@ -2347,6 +2369,12 @@ class P4Sync(Command, P4UserMap):
         self.gitOutput.close()
         self.gitError.close()
 
+        # Cleanup temporary branches created during import
+        if self.tempBranches != []:
+            for branch in self.tempBranches:
+                read_pipe("git update-ref -d %s" % branch)
+            os.rmdir(os.path.join(os.environ.get("GIT_DIR", ".git"), self.tempBranchLocation))
+
         return True
 
 class P4Rebase(Command):
-- 
1.7.7.rc2.14.g5e044.dirty