log: decorate HEAD with branch name under --decorate=full, too

The previous step to teach "log --decorate" to show "HEAD -> master"
instead of "HEAD, master" when showing the commit at the tip of the
'master' branch, when the 'master' branch is checked out, did not
work for "log --decorate=full".

The commands in the "log" family prepare commit decorations for all
refs upfront, and the actual string used in a decoration depends on
how load_ref_decorations() is called very early in the process.  By
default, "git log --decorate" stores names with common prefixes such
as "refs/heads" stripped; "git log --decorate=full" stores the full
refnames.

When the current_pointed_by_HEAD() function has to decide if "HEAD"
points at the branch a decoration describes, however, what was
passed to load_ref_decorations() to decide to strip (or keep) such a
common prefix is long lost.  This makes it impossible to reliably
tell if a decoration that stores "refs/heads/master", for example,
is the 'master' branch (under "--decorate" with prefix omitted) or
'refs/heads/master' branch (under "--decorate=full").

Keep what was passed to load_ref_decorations() in a global next to
the global variable name_decoration, and use that to decide how to
match what was read from "HEAD" and what is in a decoration.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

log-tree.c

@@ -13,6 +13,8 @@
 #include "line-log.h"
 
 static struct decoration name_decoration = { "object names" };
+static int decoration_loaded;
+static int decoration_flags;
 
 static char decoration_colors[][COLOR_MAXLEN] = {
 	GIT_COLOR_RESET,
@@ -146,9 +148,9 @@ static int add_graft_decoration(const struct commit_graft *graft, void *cb_data)
 
 void load_ref_decorations(int flags)
 {
-	static int loaded;
-	if (!loaded) {
-		loaded = 1;
+	if (!decoration_loaded) {
+		decoration_loaded = 1;
+		decoration_flags = flags;
 		for_each_ref(add_ref_decoration, &flags);
 		head_ref(add_ref_decoration, &flags);
 		for_each_commit_graft(add_graft_decoration, NULL);
@@ -196,8 +198,19 @@ static const struct name_decoration *current_pointed_by_HEAD(const struct name_d
 	branch_name = resolve_ref_unsafe("HEAD", 0, unused, &rru_flags);
 	if (!(rru_flags & REF_ISSYMREF))
 		return NULL;
+
+	if ((decoration_flags == DECORATE_SHORT_REFS)) {
 		if (!skip_prefix(branch_name, "refs/heads/", &branch_name))
 			return NULL;
+	} else {
+		/*
+		 * Each decoration has a refname in full; keep
+		 * branch_name also in full, but still make sure
+		 * HEAD is a reasonable ref.
+		 */
+		if (!starts_with(branch_name, "refs/"))
+			return NULL;
+	}
 
 	/* OK, do we have that ref in the list? */
 	for (list = decoration; list; list = list->next)

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