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>
diff --git a/contrib/coccinelle/commit.cocci b/contrib/coccinelle/commit.cocci
index c49aa55..663658a 100644
--- a/contrib/coccinelle/commit.cocci
+++ b/contrib/coccinelle/commit.cocci
@@ -10,19 +10,25 @@
- c->maybe_tree->object.oid.hash
+ get_commit_tree_oid(c)->hash
-// These excluded functions must access c->maybe_tree direcly.
@@
-identifier f !~ "^(get_commit_tree|get_commit_tree_in_graph_one|load_tree_for_commit)$";
+identifier f !~ "^set_commit_tree$";
+expression c;
+expression s;
+@@
+ f(...) {<...
+- c->maybe_tree = s
++ set_commit_tree(c, s)
+ ...>}
+
+// These excluded functions must access c->maybe_tree direcly.
+// Note that if c->maybe_tree is written somewhere outside of these
+// functions, then the recommended transformation will be bogus with
+// get_commit_tree() on the LHS.
+@@
+identifier f !~ "^(get_commit_tree|get_commit_tree_in_graph_one|load_tree_for_commit|set_commit_tree)$";
expression c;
@@
f(...) {<...
- c->maybe_tree
+ get_commit_tree(c)
...>}
-
-@@
-expression c;
-expression s;
-@@
-- get_commit_tree(c) = s
-+ c->maybe_tree = s
