commit.cocci: refactor code, avoid double rewrite

"maybe" pointer in 'struct commit' is tricky because it can be lazily
initialized to take advantage of commit-graph if available. This makes
it not safe to access directly.

This leads to a rule in commit.cocci to rewrite 'x->maybe_tree' to
'get_commit_tree(x)'. But that rule alone could lead to incorrectly
rewrite assignments, e.g. from

    x->maybe_tree = yes

to

    get_commit_tree(x) = yes

Because of this we have a second rule to revert this effect. Szeder
found out that we could do better by performing the assignment rewrite
rule first, then the remaining is read-only access and handled by the
current first rule.

For this to work, we need to transform "x->maybe_tree = y" to something
that does NOT contain "x->maybe_tree" to avoid the original first
rule. This is where set_commit_tree() comes in.

Helped-by: SZEDER Gábor <szeder.dev@gmail.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/merge-recursive.c b/merge-recursive.c
index 6c40c61c47..ca4731a719 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -163,6 +163,11 @@ static struct tree *shift_tree_object(struct repository *repo,
 	return lookup_tree(repo, &shifted);
 }
 
+static inline void set_commit_tree(struct commit *c, struct tree *t)
+{
+	c->maybe_tree = t;
+}
+
 static struct commit *make_virtual_commit(struct repository *repo,
 					  struct tree *tree,
 					  const char *comment)
@@ -170,7 +175,7 @@ static struct commit *make_virtual_commit(struct repository *repo,
 	struct commit *commit = alloc_commit_node(repo);
 
 	set_merge_remote_desc(commit, comment, (struct object *)commit);
-	commit->maybe_tree = tree;
+	set_commit_tree(commit, tree);
 	commit->object.parsed = 1;
 	return commit;
 }