[PATCH] clone: allow detached checkout when --branch takes a tag

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

This allows you to do "git clone --branch=v1.7.8 git.git" and work
right away from there. No big deal, just one more convenient step, I
think. --branch taking a tag may be confusing though.

We can still have master in this case instead of detached HEAD, which
may make more sense because we use --branch. I don't care much which
way should be used.

Like? Dislike?

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/clone.c |   20 +++++++++++++++++++-
 1 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/builtin/clone.c b/builtin/clone.c
index 8f29912..97af4bd 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -23,6 +23,7 @@
 #include "branch.h"
 #include "remote.h"
 #include "run-command.h"
+#include "tag.h"
 
 /*
  * Overall FIXMEs:
@@ -721,6 +722,14 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 			strbuf_release(&head);
 
 			if (!our_head_points_at) {
+				strbuf_addstr(&head, "refs/tags/");
+				strbuf_addstr(&head, option_branch);
+				our_head_points_at =
+					find_ref_by_name(mapped_refs, head.buf);
+				strbuf_release(&head);
+			}
+
+			if (!our_head_points_at) {
 				warning(_("Remote branch %s not found in "
 					"upstream %s, using HEAD instead"),
 					option_branch, option_origin);
@@ -750,7 +759,16 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 			      reflog_msg.buf);
 	}
 
-	if (our_head_points_at) {
+	if (our_head_points_at &&
+	    !prefixcmp(our_head_points_at->name, "refs/tags/")) {
+		const struct ref *ref = our_head_points_at;
+		struct object *o;
+
+		/* Detached HEAD */
+		o = deref_tag(parse_object(ref->old_sha1), NULL, 0);
+		update_ref(reflog_msg.buf, "HEAD", o->sha1, NULL,
+			   REF_NODEREF, DIE_ON_ERR);
+	} else if (our_head_points_at) {
 		/* Local default branch link */
 		create_symref("HEAD", our_head_points_at->name, NULL);
 		if (!option_bare) {
-- 
1.7.8.36.g69ee2