[PATCH v2 14/14] commit.h: delete 'util' field in struct commit

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

If you have come this far, you probably have seen that this 'util'
pointer is used for many different purposes. Some are not even
contained in a command code, but buried deep in common code with no
clue who will use it and how.

The move to using commit-slab gives us a much better picture of how
some piece of data is associated with a commit and what for. Since
nobody uses 'util' pointer anymore, we can retire so that nobody will
abuse it again. commit-slab will be the way forward for associating
data to a commit.

As a side benefit, this shrinks struct commit by 8 bytes (on 64-bit
architecture) which should help reduce memory usage for reachability
test a bit. This is also what commit-slab is invented for [1].

[1] 96c4f4a370 (commit: allow associating auxiliary info on-demand -
2013-04-09)

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 commit.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/commit.h b/commit.h
index 838f6a6b26..70371e111e 100644
--- a/commit.h
+++ b/commit.h
@@ -18,12 +18,16 @@ struct commit_list {
 
 struct commit {
 	struct object object;
-	void *util;
 	unsigned int index;
 	timestamp_t date;
 	struct commit_list *parents;
 	struct tree *tree;
 	uint32_t graph_pos;
+	/*
+	 * Do not add more fields here unless it's _very_ often
+	 * used. Use commit-slab to associate more data with a commit
+	 * instead.
+	 */
 };
 
 extern int save_commit_buffer;
-- 
2.17.0.705.g3525833791