[PATCH v4 6/6] cocci: generalize "unused" rule to cover more than "strbuf"

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

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>
---
 builtin/repack.c                    |  2 --
 contrib/coccinelle/tests/unused.c   | 27 +++++++++++++++++++++++++++
 contrib/coccinelle/tests/unused.res | 15 +++++++++++++++
 contrib/coccinelle/unused.cocci     | 19 +++++++++++++++----
 4 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/builtin/repack.c b/builtin/repack.c
index 4a7ae4cf489..482b66f57d6 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -727,7 +727,6 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	struct string_list_item *item;
 	struct string_list names = STRING_LIST_INIT_DUP;
-	struct string_list rollback = STRING_LIST_INIT_NODUP;
 	struct string_list existing_nonkept_packs = STRING_LIST_INIT_DUP;
 	struct string_list existing_kept_packs = STRING_LIST_INIT_DUP;
 	struct pack_geometry *geometry = NULL;
@@ -1117,7 +1116,6 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	}
 
 	string_list_clear(&names, 0);
-	string_list_clear(&rollback, 0);
 	string_list_clear(&existing_nonkept_packs, 0);
 	string_list_clear(&existing_kept_packs, 0);
 	clear_pack_geometry(geometry);
diff --git a/contrib/coccinelle/tests/unused.c b/contrib/coccinelle/tests/unused.c
index 495ae58ccf1..8294d734ba4 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 b3b71053ed6..6d3e745683c 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 56530498d17..d84046f82ea 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 != \( I \| &I \)
-- 
2.37.0.913.g50625c3f077