git p4: create p4/HEAD on initial clone

There is code to create a symbolic reference from p4/HEAD to
p4/master.  This allows saying "git show p4" as a shortcut
to "git show p4/master", for example.

But this reference was only created on the second "git p4 sync"
(or first sync after a clone).  Make it work on the initial
clone or sync.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -2772,10 +2772,7 @@ class P4Sync(Command, P4UserMap):
             self.branch = self.refPrefix + "master"
             if gitBranchExists("refs/heads/p4") and self.importIntoRemotes:
                 system("git update-ref %s refs/heads/p4" % self.branch)
-                system("git branch -D p4");
-            # create it /after/ importing, when master exists
-            if not gitBranchExists(self.refPrefix + "HEAD") and self.importIntoRemotes and gitBranchExists(self.branch):
-                system("git symbolic-ref %sHEAD %s" % (self.refPrefix, self.branch))
+                system("git branch -D p4")
 
         # accept either the command-line option, or the configuration variable
         if self.useClientSpec:
@@ -3007,6 +3004,13 @@ class P4Sync(Command, P4UserMap):
                 read_pipe("git update-ref -d %s" % branch)
             os.rmdir(os.path.join(os.environ.get("GIT_DIR", ".git"), self.tempBranchLocation))
 
+        # Create a symbolic ref p4/HEAD pointing to p4/<branch> to allow
+        # a convenient shortcut refname "p4".
+        if self.importIntoRemotes:
+            head_ref = self.refPrefix + "HEAD"
+            if not gitBranchExists(head_ref) and gitBranchExists(self.branch):
+                system(["git", "symbolic-ref", head_ref, self.branch])
+
         return True
 
 class P4Rebase(Command):

t/t9806-git-p4-options.sh

@@ -83,6 +83,29 @@ test_expect_failure 'sync --branch updates specified branch' '
 	)
 '
 
+# allows using the refname "p4" as a short name for p4/master
+test_expect_success 'clone creates HEAD symbolic reference' '
+	git p4 clone --dest="$git" //depot &&
+	test_when_finished cleanup_git &&
+	(
+		cd "$git" &&
+		git rev-parse --verify refs/remotes/p4/master >master &&
+		git rev-parse --verify p4 >p4 &&
+		test_cmp master p4
+	)
+'
+
+test_expect_success 'clone --branch creates HEAD symbolic reference' '
+	git p4 clone --branch=refs/remotes/p4/sb --dest="$git" //depot &&
+	test_when_finished cleanup_git &&
+	(
+		cd "$git" &&
+		git rev-parse --verify refs/remotes/p4/sb >sb &&
+		git rev-parse --verify p4 >p4 &&
+		test_cmp sb p4
+	)
+'
+
 test_expect_success 'clone --changesfile' '
 	test_when_finished "rm cf" &&
 	printf "1\n3\n" >cf &&