Merge branch 'mg/log-decorate-HEAD'

Output from "git log --decorate" mentions HEAD when it points at a
tip of an branch differently from a detached HEAD.

This is a potentially backward-incompatible change.

* mg/log-decorate-HEAD:
  log: decorate HEAD with branch name

log-tree.c

@@ -172,6 +172,43 @@ static void show_children(struct rev_info *opt, struct commit *commit, int abbre
 	}
 }
 
+/*
+ * Do we have HEAD in the output, and also the branch it points at?
+ * If so, find that decoration entry for that current branch.
+ */
+static const struct name_decoration *current_pointed_by_HEAD(const struct name_decoration *decoration)
+{
+	const struct name_decoration *list, *head = NULL;
+	const char *branch_name = NULL;
+	unsigned char unused[20];
+	int rru_flags;
+
+	/* First find HEAD */
+	for (list = decoration; list; list = list->next)
+		if (list->type == DECORATION_REF_HEAD) {
+			head = list;
+			break;
+		}
+	if (!head)
+		return NULL;
+
+	/* Now resolve and find the matching current branch */
+	branch_name = resolve_ref_unsafe("HEAD", 0, unused, &rru_flags);
+	if (!(rru_flags & REF_ISSYMREF))
+		return NULL;
+	if (!skip_prefix(branch_name, "refs/heads/", &branch_name))
+		return NULL;
+
+	/* OK, do we have that ref in the list? */
+	for (list = decoration; list; list = list->next)
+		if ((list->type == DECORATION_REF_LOCAL) &&
+		    !strcmp(branch_name, list->name)) {
+			return list;
+		}
+
+	return NULL;
+}
+
 /*
  * The caller makes sure there is no funny color before calling.
  * format_decorations_extended makes sure the same after return.
@@ -184,6 +221,7 @@ void format_decorations_extended(struct strbuf *sb,
 			const char *suffix)
 {
 	const struct name_decoration *decoration;
+	const struct name_decoration *current_and_HEAD;
 	const char *color_commit =
 		diff_get_color(use_color, DIFF_COMMIT);
 	const char *color_reset =
@@ -192,16 +230,37 @@ void format_decorations_extended(struct strbuf *sb,
 	decoration = get_name_decoration(&commit->object);
 	if (!decoration)
 		return;
+
+	current_and_HEAD = current_pointed_by_HEAD(decoration);
 	while (decoration) {
+		/*
+		 * When both current and HEAD are there, only
+		 * show HEAD->current where HEAD would have
+		 * appeared, skipping the entry for current.
+		 */
+		if (decoration != current_and_HEAD) {
 			strbuf_addstr(sb, color_commit);
 			strbuf_addstr(sb, prefix);
 			strbuf_addstr(sb, color_reset);
 			strbuf_addstr(sb, decorate_get_color(use_color, decoration->type));
 			if (decoration->type == DECORATION_REF_TAG)
 				strbuf_addstr(sb, "tag: ");
+
 			strbuf_addstr(sb, decoration->name);
+
+			if (current_and_HEAD &&
+			    decoration->type == DECORATION_REF_HEAD) {
 				strbuf_addstr(sb, color_reset);
+				strbuf_addstr(sb, color_commit);
+				strbuf_addstr(sb, " -> ");
+				strbuf_addstr(sb, color_reset);
+				strbuf_addstr(sb, decorate_get_color(use_color, current_and_HEAD->type));
+				strbuf_addstr(sb, current_and_HEAD->name);
+			}
+			strbuf_addstr(sb, color_reset);
+
 			prefix = separator;
+		}
 		decoration = decoration->next;
 	}
 	strbuf_addstr(sb, color_commit);

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)
 Merge: 9a6d494 c7a2ab9
 Author: A U Thor <author@example.com>
 Date:   Mon Jun 26 00:04:00 2006 +0000

t/t4207-log-decoration-colors.sh

@@ -44,10 +44,10 @@ test_expect_success setup '
 '
 
 cat >expected <<EOF
-${c_commit}COMMIT_ID${c_reset}${c_commit} (${c_reset}${c_HEAD}HEAD${c_reset}${c_commit},\
+${c_commit}COMMIT_ID${c_reset}${c_commit} (${c_reset}${c_HEAD}HEAD${c_reset}${c_commit} ->\
+ ${c_reset}${c_branch}master${c_reset}${c_commit},\
  ${c_reset}${c_tag}tag: v1.0${c_reset}${c_commit},\
- ${c_reset}${c_tag}tag: B${c_reset}${c_commit},\
- ${c_reset}${c_branch}master${c_reset}${c_commit})${c_reset} B
+ ${c_reset}${c_tag}tag: B${c_reset}${c_commit})${c_reset} B
 ${c_commit}COMMIT_ID${c_reset}${c_commit} (${c_reset}${c_tag}tag: A1${c_reset}${c_commit},\
  ${c_reset}${c_remoteBranch}other/master${c_reset}${c_commit})${c_reset} A1
 ${c_commit}COMMIT_ID${c_reset}${c_commit} (${c_reset}${c_stash}refs/stash${c_reset}${c_commit})${c_reset}\