[PATCH] defer expensive load_ref_decorations until needed

[Phil Hord]

With many thousands of references, a simple `git rev-parse HEAD` may take
more than a second to return because it first loads all the refs into
memory even though it will never use them.

Defer loading any references until we actually need them.

Signed-off-by: Phil Hord <phil.h...@gmail.com>
---
 log-tree.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/log-tree.c b/log-tree.c
index 3b904f037..c1509f8b9 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -84,8 +84,10 @@ void add_name_decoration(enum decoration_type type, const 
char *name, struct obj
        res->next = add_decoration(&name_decoration, obj, res);
 }
 
+static void maybe_load_ref_decorations();
 const struct name_decoration *get_name_decoration(const struct object *obj)
 {
+       maybe_load_ref_decorations();
        return lookup_decoration(&name_decoration, obj);
 }
 
@@ -150,10 +152,13 @@ static int add_graft_decoration(const struct commit_graft 
*graft, void *cb_data)
 
 void load_ref_decorations(int flags)
 {
-       if (!decoration_loaded) {
+       decoration_flags = flags;
+}
 
+static void maybe_load_ref_decorations()
+{
+       if (!decoration_loaded) {
                decoration_loaded = 1;
-               decoration_flags = flags;
                for_each_ref(add_ref_decoration, NULL);
                head_ref(add_ref_decoration, NULL);
                for_each_commit_graft(add_graft_decoration, NULL);
-- 
2.15.0.471.g17a719cfe.dirty