coccinelle: avoid wrong transformation suggestions from commit.cocci

szeder · gitster · commit 279ffad17dcc · 2018-05-02T13:38:52.000+09:00
The semantic patch 'contrib/coccinelle/commit.cocci' added in 2e27bd7 (treewide: replace maybe_tree with accessor methods, 2018-04-06) is supposed to "ensure that all references to the 'maybe_tree' member of struct commit are either mutations or accesses through get_commit_tree()". So get_commit_tree() clearly must be able to directly access the 'maybe_tree' member, and 'commit.cocci' has a bit of a roundabout workaround to ensure that get_commit_tree()'s direct access in its return statement is not transformed: after all references to 'maybe_tree' have been transformed to a call to get_commit_tree(), including the reference in get_commit_tree() itself, the last rule transforms back a 'return get_commit_tree()' statement, back then found only in get_commit_tree() itself, to a direct access. Unfortunately, already the very next commit shows that this workaround is insufficient: 7b8a21d (commit-graph: lazy-load trees for commits, 2018-04-06) extends get_commit_tree() with a condition directly accessing the 'maybe_tree' member, and Coccinelle with 'commit.cocci' promptly detects it and suggests a transformation to avoid it. This transformation is clearly wrong, because calling get_commit_tree() to access 'maybe_tree' _in_ get_commit_tree() would obviously lead to recursion. Furthermore, the same commit added another, more specialized getter function get_commit_tree_in_graph(), whose legitimate direct access to 'maybe_tree' triggers a similar wrong transformation suggestion. Exclude both of these getter functions from the general rule in 'commit.cocci' that matches their direct accesses to 'maybe_tree'. Also exclude load_tree_for_commit(), which, as static helper funcion of get_commit_tree_in_graph(), has legitimate direct access to 'maybe_tree' as well. The last rule transforming back 'return get_commit_tree()' statements to direct accesses thus became unnecessary, remove it. Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com> Acked-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/contrib/coccinelle/commit.cocci b/contrib/coccinelle/commit.cocci
@@ -10,21 +10,19 @@ expression c;
 - 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|load_tree_for_commit)$";
 expression c;
 @@
+  f(...) {...
 - c->maybe_tree
 + get_commit_tree(c)
+  ...}
 
 @@
 expression c;
 expression s;
 @@
 - get_commit_tree(c) = s
 + c->maybe_tree = s
-
-@@
-expression c;
-@@
-- return get_commit_tree(c);
-+ return c->maybe_tree;
