[PATCH] log: decorate detached HEAD differently

[Michael J Gruber <git@drmicha.warpmail.net>]

"git status" and "git branch" let the user know when the HEAD is
detached, as well as the current branch, while "git log --decorate" does not.

Change the decoration by a non-detached HEAD pointing to branch foo to
"HEAD->foo". This can be seen as giving more information about the
decoration item itself in the same way as we prefix tags by "tag: ".

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
---

Notes:
    v2 decorates the HEAD pointing to master as "HEAD->master", a detached
    HEAD just as "HEAD". The "->" hopefully conveys the symlink nature - a
    "=" would be confusing.
    
    Somehow I still prefer "detached HEAD", dunno. Maybe in addition?
    
    Note that now a checked branch is listed twice, once as target of the
    HEAD, once as branch: They are two different refs and colored differently.

 log-tree.c                             | 8 +++++++-
 t/t4013/diff.log_--decorate=full_--all | 2 +-
 t/t4013/diff.log_--decorate_--all      | 2 +-
 t/t4207-log-decoration-colors.sh       | 2 +-
 4 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/log-tree.c b/log-tree.c
index 7f0890e..38862bb 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -118,8 +118,11 @@ static int add_ref_decoration(const char *refname, const unsigned char *sha1, in
 		type = DECORATION_REF_TAG;
 	else if (!strcmp(refname, "refs/stash"))
 		type = DECORATION_REF_STASH;
-	else if (!strcmp(refname, "HEAD"))
+	else if (!strcmp(refname, "HEAD")) {
+		unsigned char junk_sha1[20];
 		type = DECORATION_REF_HEAD;
+		refname = resolve_ref_unsafe("HEAD", 0, junk_sha1, NULL);
+	}
 
 	if (!cb_data || *(int *)cb_data == DECORATE_SHORT_REFS)
 		refname = prettify_refname(refname);
@@ -198,6 +201,9 @@ void format_decorations_extended(struct strbuf *sb,
 		strbuf_addstr(sb, decorate_get_color(use_color, decoration->type));
 		if (decoration->type == DECORATION_REF_TAG)
 			strbuf_addstr(sb, "tag: ");
+		else if (decoration->type == DECORATION_REF_HEAD &&
+			 strcmp(decoration->name, "HEAD"))
+			strbuf_addstr(sb, "HEAD->");
 		strbuf_addstr(sb, decoration->name);
 		strbuf_addstr(sb, color_reset);
 		prefix = separator;
diff --git a/t/t4013/diff.log_--decorate=full_--all b/t/t4013/diff.log_--decorate=full_--all
index 44d4525..3758ae9 100644
--- a/t/t4013/diff.log_--decorate=full_--all
+++ b/t/t4013/diff.log_--decorate=full_--all
@@ -5,7 +5,7 @@ Date:   Mon Jun 26 00:06:00 2006 +0000
 
     Rearranged lines in dir/sub
 
-commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (HEAD, refs/heads/master)
+commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (HEAD->refs/heads/master, refs/heads/master)
 Merge: 9a6d494 c7a2ab9
 Author: A U Thor <author@example.com>
 Date:   Mon Jun 26 00:04:00 2006 +0000
diff --git a/t/t4013/diff.log_--decorate_--all b/t/t4013/diff.log_--decorate_--all
index 27d3eab..df702ae 100644
--- a/t/t4013/diff.log_--decorate_--all
+++ b/t/t4013/diff.log_--decorate_--all
@@ -5,7 +5,7 @@ Date:   Mon Jun 26 00:06:00 2006 +0000
 
     Rearranged lines in dir/sub
 
-commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (HEAD, master)
+commit 59d314ad6f356dd08601a4cd5e530381da3e3c64 (HEAD->master, master)
 Merge: 9a6d494 c7a2ab9
 Author: A U Thor <author@example.com>
 Date:   Mon Jun 26 00:04:00 2006 +0000
diff --git a/t/t4207-log-decoration-colors.sh b/t/t4207-log-decoration-colors.sh
index 925f577..0437ff2 100755
--- a/t/t4207-log-decoration-colors.sh
+++ b/t/t4207-log-decoration-colors.sh
@@ -44,7 +44,7 @@ test_expect_success setup '
 '
 
 cat >expected <<EOF
-${c_commit}COMMIT_ID${c_reset}${c_commit} (${c_HEAD}HEAD${c_reset}${c_commit},\
+${c_commit}COMMIT_ID${c_reset}${c_commit} (${c_HEAD}HEAD->master${c_reset}${c_commit},\
  ${c_tag}tag: v1.0${c_reset}${c_commit},\
  ${c_tag}tag: B${c_reset}${c_commit},\
  ${c_branch}master${c_reset}${c_commit})${c_reset} B
-- 
2.3.1.303.g5174db1