cocci: generalize "unused" rule to cover more than "strbuf"

Generalize the newly added "unused.cocci" rule to find more than just
"struct strbuf", let's have it find the same unused patterns for
"struct string_list", as well as other code that uses
similar-looking *_{release,clear,free}() and {release,clear,free}_*()
functions.

We're intentionally loose in accepting e.g. a "strbuf_init(&sb)"
followed by a "string_list_clear(&sb, 0)".  It's assumed that the
compiler will catch any such invalid code, i.e. that our
constructors/destructors don't take a "void *".

See [1] for example of code that would be covered by the
"get_worktrees()" part of this rule. We'd still need work that the
series is based on (we were passing "worktrees" to a function), but
could now do the change in [1] automatically.

1. https://lore.kernel.org/git/Yq6eJFUPPTv%2Fzc0o@coredump.intra.peff.net/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 57 insertions, 4 deletions

diff --git a/contrib/coccinelle/tests/unused.c b/contrib/coccinelle/tests/unused.c
index 495ae58ccf..8294d734ba 100644
--- a/contrib/coccinelle/tests/unused.c
+++ b/contrib/coccinelle/tests/unused.c
@@ -53,3 +53,30 @@ void test_strbuf(void)
 		return;
 	strbuf_release(&sb8);
 }
+
+void test_other(void)
+{
+	struct string_list l = STRING_LIST_INIT_DUP;
+	struct strbuf sb = STRBUF_INIT;
+
+	string_list_clear(&l, 0);
+	string_list_clear(&sb, 0);
+}
+
+void test_worktrees(void)
+{
+	struct worktree **w1 = get_worktrees();
+	struct worktree **w2 = get_worktrees();
+	struct worktree **w3;
+	struct worktree **w4;
+
+	w3 = get_worktrees();
+	w4 = get_worktrees();
+
+	use_it(w4);
+
+	free_worktrees(w1);
+	free_worktrees(w2);
+	free_worktrees(w3);
+	free_worktrees(w4);
+}
diff --git a/contrib/coccinelle/tests/unused.res b/contrib/coccinelle/tests/unused.res
index b3b71053ed..6d3e745683 100644
--- a/contrib/coccinelle/tests/unused.res
+++ b/contrib/coccinelle/tests/unused.res
@@ -28,3 +28,18 @@ void test_strbuf(void)
 	if (when_strict())
 		return;
 }
+
+void test_other(void)
+{
+}
+
+void test_worktrees(void)
+{
+	struct worktree **w4;
+
+	w4 = get_worktrees();
+
+	use_it(w4);
+
+	free_worktrees(w4);
+}
diff --git a/contrib/coccinelle/unused.cocci b/contrib/coccinelle/unused.cocci
index 56530498d1..d84046f82e 100644
--- a/contrib/coccinelle/unused.cocci
+++ b/contrib/coccinelle/unused.cocci
@@ -4,10 +4,13 @@
 @@
 type T;
 identifier I;
-constant INIT_MACRO =~ "^STRBUF_INIT$";
+// STRBUF_INIT, but also e.g. STRING_LIST_INIT_DUP (so no anchoring)
+constant INIT_MACRO =~ "_INIT";
 identifier MALLOC1 =~ "^x?[mc]alloc$";
-identifier INIT_CALL1 =~ "^strbuf_init$";
-identifier REL1 =~ "^strbuf_(release|reset)$";
+identifier INIT_ASSIGN1 =~ "^get_worktrees$";
+identifier INIT_CALL1 =~ "^[a-z_]*_init$";
+identifier REL1 =~ "^[a-z_]*_(release|reset|clear|free)$";
+identifier REL2 =~ "^(release|clear|free)_[a-z_]*$";
 @@
 
 (
@@ -18,15 +21,23 @@ identifier REL1 =~ "^strbuf_(release|reset)$";
 - T I = INIT_MACRO;
 |
 - T I = MALLOC1(...);
+|
+- T I = INIT_ASSIGN1(...);
 )
 
 <... when != \( I \| &I \)
 (
 - \( INIT_CALL1 \)( \( I \| &I \), ...);
 |
+- I = \( INIT_ASSIGN1 \)(...);
+|
 - I = MALLOC1(...);
 )
 ...>
 
-- \( REL1 \)( \( &I \| I \) );
+(
+- \( REL1 \| REL2 \)( \( I \| &I \), ...);
+|
+- \( REL1 \| REL2 \)( \( &I \| I \) );
+)
   ... when != \( I \| &I \)