Add git-symbolic-ref

This adds the counterpart of git-update-ref that lets you read
and create "symbolic refs".  By default it uses a symbolic link
to represent ".git/HEAD -> refs/heads/master", but it can be compiled
to use the textfile symbolic ref.

The places that did 'readlink .git/HEAD' and 'ln -s refs/heads/blah
.git/HEAD' have been converted to use new git-symbolic-ref command, so
that they can deal with either implementation.

Signed-off-by: Junio C Hamano <junio@twinsun.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/symbolic-ref.c b/symbolic-ref.c
new file mode 100644
index 000000000..af087d211
--- /dev/null
+++ b/symbolic-ref.c
@@ -0,0 +1,34 @@
+#include "cache.h"
+
+static const char git_symbolic_ref_usage[] =
+"git-symbolic-ref name [ref]";
+
+static int check_symref(const char *HEAD)
+{
+	unsigned char sha1[20];
+	const char *git_HEAD = strdup(git_path("%s", HEAD));
+	const char *git_refs_heads_master = resolve_ref(git_HEAD, sha1, 0);
+	if (git_refs_heads_master) {
+		/* we want to strip the .git/ part */
+		int pfxlen = strlen(git_HEAD) - strlen(HEAD);
+		puts(git_refs_heads_master + pfxlen);
+	}
+	else
+		die("No such ref: %s", HEAD);
+}
+
+int main(int argc, const char **argv)
+{
+	setup_git_directory();
+	switch (argc) {
+	case 2:
+		check_symref(argv[1]);
+		break;
+	case 3:
+		create_symref(strdup(git_path("%s", argv[1])), argv[2]);
+		break;
+	default:
+		usage(git_symbolic_ref_usage);
+	}
+	return 0;
+}