Fix branches file configuration

Fetched remote branch from .git/branches/foo should fetch into
refs/heads/foo.  Also when partial URL is given, the fetched head should
always be remote HEAD, and the result should not be stored anywhere.
Signed-off-by: NDaniel Barkalow <barkalow@iabervon.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

remote.c

@@ -171,7 +171,7 @@ static void read_branches_file(struct remote *remote)
 {
 	const char *slash = strchr(remote->name, '/');
 	char *frag;
-	char *branch;
+	struct strbuf branch;
 	int n = slash ? slash - remote->name : 1000;
 	FILE *f = fopen(git_path("branches/%.*s", n, remote->name), "r");
 	char *s, *p;
@@ -197,17 +197,33 @@ static void read_branches_file(struct remote *remote)
 	strcpy(p, s);
 	if (slash)
 		strcat(p, slash);
+
+	/*
+	 * With "slash", e.g. "git fetch jgarzik/netdev-2.6" when
+	 * reading from $GIT_DIR/branches/jgarzik fetches "HEAD" from
+	 * the partial URL obtained from the branches file plus
+	 * "/netdev-2.6" and does not store it in any tracking ref.
+	 * #branch specifier in the file is ignored.
+	 *
+	 * Otherwise, the branches file would have URL and optionally
+	 * #branch specified.  The "master" (or specified) branch is
+	 * fetched and stored in the local branch of the same name.
+	 */
+	strbuf_init(&branch, 0);
 	frag = strchr(p, '#');
 	if (frag) {
 		*(frag++) = '\0';
-		branch = xmalloc(strlen(frag) + 12);
-		strcpy(branch, "refs/heads/");
-		strcat(branch, frag);
+		strbuf_addf(&branch, "refs/heads/%s", frag);
+	} else
+		strbuf_addstr(&branch, "refs/heads/master");
+	if (!slash) {
+		strbuf_addf(&branch, ":refs/heads/%s", remote->name);
 	} else {
-		branch = "refs/heads/master";
+		strbuf_reset(&branch);
+		strbuf_addstr(&branch, "HEAD:");
 	}
 	add_url(remote, p);
-	add_fetch_refspec(remote, branch);
+	add_fetch_refspec(remote, strbuf_detach(&branch, 0));
 	remote->fetch_tags = 1; /* always auto-follow */
 }