[PATCH v3 4/4] 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.

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/unused.cocci | 31 ++++++++++++++++++++++++-------
 2 files changed, 24 insertions(+), 9 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/unused.cocci b/contrib/coccinelle/unused.cocci
index 9f0101c1350..a1b09d2d73d 100644
--- a/contrib/coccinelle/unused.cocci
+++ b/contrib/coccinelle/unused.cocci
@@ -1,5 +1,5 @@
 // This rule finds sequences of "unused" declerations and uses of
-// "struct strbuf".
+// "struct strbuf" and other common types.
 //
 // I.e. this finds cases where we only declare the variable, and then
 // release it, e.g.:
@@ -20,14 +20,18 @@
 @@
 type T;
 identifier I;
-// STRBUF_INIT
-constant INIT_MACRO =~ "^STRBUF_INIT$";
+// STRBUF_INIT, but also e.g. STRING_LIST_INIT_DUP (so no anchoring)
+constant INIT_MACRO =~ "_INIT";
 // x[mc]alloc() etc.
 identifier MALLOC1 =~ "^x?[mc]alloc$";
+// I = get_worktrees() etc.
+identifier INIT_ASSIGN1 =~ "^get_worktrees$";
 // strbuf_init(&I, ...) etc.
-identifier INIT_CALL1 =~ "^strbuf_init$";
-// strbuf_release()
-identifier REL1 =~ "^strbuf_release$";
+identifier INIT_CALL1 =~ "^[a-z_]*_init$";
+// stbuf_release(), string_list_clear() etc.
+identifier REL1 =~ "^[a-z_]*_(release|clear|free)$";
+// release_patch(), clear_pathspec() etc.
+identifier REL2 =~ "^(release|clear|free)_[a-z_]*$";
 @@
 
 // .. A declaration like "struct strbuf buf;"...
@@ -52,6 +56,10 @@ identifier REL1 =~ "^strbuf_release$";
 // "strbuf_init(&buf, ...)" ...
 - \( INIT_CALL1 \)( \( I \| &I \), ...);
 |
+// .. or e.g. "worktrees = get_worktrees();", i.e. a known "assignment
+// init" ...
+- I = \( INIT_ASSIGN1 \)(...);
+|
 // .. or to follow-up a "struct strbuf *buf" with e.g. "buf =
 // xmalloc(...)" (which may in turn be followed-up by a
 // "strbuf_init()", which we'll match with INIT_CALL1) ...
@@ -61,11 +69,20 @@ identifier REL1 =~ "^strbuf_release$";
 
 // ... and then no mention of "buf" or "&buf" until we get to a
 // strbuf_release(&buf) at the end ...
-- \( REL1 \)( \( &I \| I \) );
+(
+- \( REL1 \| REL2 \)( \( I \| &I \), ...);
+|
+- \( REL1 \| REL2 \)( \( &I \| I \) );
+)
 // ... and no use *after* either, e.g. we don't want to delete
 // init/strbuf_release() patterns, where "&buf" could be used
 // afterwards.
   ... when != \( I \| &I \)
+// Note that we're intentionally loose in accepting e.g. a
+// "strbuf_init(&buf)" followed by a "string_list_clear(&buf,
+// 0)". It's assumed that the compiler will catch any such invalid
+// code, i.e. that our constructors/destructors don't take a "void *".
+//
 // This rule also isn't capable of finding cases where &buf is used,
 // but only to e.g. pass that variable to a static function which
 // doesn't use it. The analysis is only function-local.
-- 
2.37.0.900.g4d0de1cceb2