git-p4: fix P4 label import for unprocessed commits

With --detect-labels enabled, git-p4 will try to create tags
using git fast-import by writing a "tag" clause to the
fast-import stream.

If the commit that the tag references has not yet actually
been processed by fast-import, then the tag can't be created
and git-p4 fails to import the P4 label.

Teach git-p4 to use fast-import "marks" when creating tags
which reference commits created during the current run of the
program.

Commits created before the current run are still referenced
in the old way using a normal git commit.

Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -2322,8 +2322,11 @@ class P4Sync(Command, P4UserMap):
         else:
             return "%s <a@b>" % userid
 
-    # Stream a p4 tag
     def streamTag(self, gitStream, labelName, labelDetails, commit, epoch):
+        """ Stream a p4 tag.
+        commit is either a git commit, or a fast-import mark, ":<p4commit>"
+        """
+
         if verbose:
             print "writing tag %s for commit %s" % (labelName, commit)
         gitStream.write("tag %s\n" % labelName)
@@ -2374,7 +2377,7 @@ class P4Sync(Command, P4UserMap):
             self.clientSpecDirs.update_client_spec_path_cache(files)
 
         self.gitStream.write("commit %s\n" % branch)
-#        gitStream.write("mark :%s\n" % details["change"])
+        self.gitStream.write("mark :%s\n" % details["change"])
         self.committedChanges.add(int(details["change"]))
         committer = ""
         if author not in self.users:
@@ -2493,13 +2496,19 @@ class P4Sync(Command, P4UserMap):
             if change.has_key('change'):
                 # find the corresponding git commit; take the oldest commit
                 changelist = int(change['change'])
-                gitCommit = read_pipe(["git", "rev-list", "--max-count=1",
-                     "--reverse", ":/\[git-p4:.*change = %d\]" % changelist], ignore_error=True)
-                if len(gitCommit) == 0:
-                    print "importing label %s: could not find git commit for changelist %d" % (name, changelist)
-                else:
-                    gitCommit = gitCommit.strip()
+                if changelist in self.committedChanges:
+                    gitCommit = ":%d" % changelist       # use a fast-import mark
                     commitFound = True
+                else:
+                    gitCommit = read_pipe(["git", "rev-list", "--max-count=1",
+                        "--reverse", ":/\[git-p4:.*change = %d\]" % changelist], ignore_error=True)
+                    if len(gitCommit) == 0:
+                        print "importing label %s: could not find git commit for changelist %d" % (name, changelist)
+                    else:
+                        commitFound = True
+                        gitCommit = gitCommit.strip()
+
+                if commitFound:
                     # Convert from p4 time format
                     try:
                         tmwhen = time.strptime(labelDetails['Update'], "%Y/%m/%d %H:%M:%S")

t/t9811-git-p4-label-import.sh

@@ -222,7 +222,7 @@ p4_head_revision() {
 # has not been seen. The presence of a label on a commit
 # we haven't seen should not cause git-p4 to fail. It should
 # merely skip that label, and still import other labels.
-test_expect_failure 'importing labels with missing revisions' '
+test_expect_success 'importing labels with missing revisions' '
 	test_when_finished cleanup_git &&
 	(
 		rm -fr "$cli" "$git" &&