git-p4: Added support for automatically importing newly appearing perforce branches.

If a change in a p4 "branch" appears that hasn't seen any previous commit and
that has a known branch mapping we now try to import it properly. First we
find the p4 change of the source branch that the new p4 branch is based on. Then
we using git rev-list --bisect to locate the corresponding git commit to that change.
Finally we import all changes in the new p4 branch up to the current change and resume
with the regular import.

Signed-off-by: Simon Hausmann <simon@lst.de>

contrib/fast-import/git-p4

@@ -1127,6 +1127,67 @@ class P4Sync(Command):
 
         return self.refPrefix + self.projectName + branch
 
+    def gitCommitByP4Change(self, ref, change):
+        if self.verbose:
+            print "looking in ref " + ref + " for change %s using bisect..." % change
+
+        earliestCommit = ""
+        latestCommit = parseRevision(ref)
+
+        while True:
+            if self.verbose:
+                print "trying: earliest %s latest %s" % (earliestCommit, latestCommit)
+            next = read_pipe("git rev-list --bisect %s %s" % (latestCommit, earliestCommit)).strip()
+            if len(next) == 0:
+                if self.verbose:
+                    print "argh"
+                return ""
+            log = extractLogMessageFromGitCommit(next)
+            settings = extractSettingsGitLog(log)
+            currentChange = int(settings['change'])
+            if self.verbose:
+                print "current change %s" % currentChange
+
+            if currentChange == change:
+                if self.verbose:
+                    print "found %s" % next
+                return next
+
+            if currentChange < change:
+                earliestCommit = "^%s" % next
+            else:
+                latestCommit = "%s" % next
+
+        return ""
+
+    def importNewBranch(self, branch, maxChange):
+        # make fast-import flush all changes to disk and update the refs using the checkpoint
+        # command so that we can try to find the branch parent in the git history
+        self.gitStream.write("checkpoint\n\n");
+        self.gitStream.flush();
+        branchPrefix = self.depotPaths[0] + branch + "/"
+        range = "@1,%s" % maxChange
+        #print "prefix" + branchPrefix
+        changes = p4ChangesForPaths([branchPrefix], range)
+        if len(changes) <= 0:
+            return False
+        firstChange = changes[0]
+        #print "first change in branch: %s" % firstChange
+        sourceBranch = self.knownBranches[branch]
+        sourceDepotPath = self.depotPaths[0] + sourceBranch
+        sourceRef = self.gitRefForBranch(sourceBranch)
+        #print "source " + sourceBranch
+
+        branchParentChange = int(p4Cmd("changes -m 1 %s...@1,%s" % (sourceDepotPath, firstChange))["change"])
+        #print "branch parent: %s" % branchParentChange
+        gitParent = self.gitCommitByP4Change(sourceRef, branchParentChange)
+        if len(gitParent) > 0:
+            self.initialParents[self.gitRefForBranch(branch)] = gitParent
+            #print "parent git commit: %s" % gitParent
+
+        self.importChanges(changes)
+        return True
+
     def importChanges(self, changes):
         cnt = 1
         for change in changes:
@@ -1159,7 +1220,18 @@ class P4Sync(Command):
                             parent = self.knownBranches[branch]
                             if parent == branch:
                                 parent = ""
-                            elif self.verbose:
+                            else:
+                                fullBranch = self.projectName + branch
+                                if fullBranch not in self.p4BranchesInGit:
+                                    if not self.silent:
+                                        print("\n    Importing new branch %s" % fullBranch);
+                                    if self.importNewBranch(branch, change - 1):
+                                        parent = ""
+                                        self.p4BranchesInGit.append(fullBranch)
+                                    if not self.silent:
+                                        print("\n    Resuming with change %s" % change);
+
+                                if self.verbose:
                                     print "parent determined through known branches: %s" % parent
 
                         branch = self.gitRefForBranch(branch)