[PATCH v3 2/4] cocci: catch unused "strbuf" using an xmalloc() pattern

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

There's no current matches for this rule, but it will match both:

	struct strbuf *buf = xmalloc(sizeof(struct strbuf));
	strbuf_init(buf, 0);
	strbuf_release(buf);

And:

	struct strbuf *buf;

	buf = xmalloc(sizeof(struct strbuf));
	strbuf_init(buf, 0);
	strbuf_release(buf);

Note that we'd also match a strbuf_init() before the xmalloc(), but
we're not seeking to be so strict as to make checks that the compiler
will catch for us redundant, and saying we'll match either "init" or
"xmalloc" lines makes the rule simpler.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 contrib/coccinelle/unused.cocci | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/contrib/coccinelle/unused.cocci b/contrib/coccinelle/unused.cocci
index bc26d39b313..43942f3cd4f 100644
--- a/contrib/coccinelle/unused.cocci
+++ b/contrib/coccinelle/unused.cocci
@@ -22,6 +22,8 @@ type T;
 identifier I;
 // STRBUF_INIT
 constant INIT_MACRO =~ "^STRBUF_INIT$";
+// x[mc]alloc() etc.
+identifier MALLOC1 =~ "^x?[mc]alloc$";
 // strbuf_init(&I, ...) etc.
 identifier INIT_CALL1 =~ "^strbuf_init$";
 // strbuf_release()
@@ -37,15 +39,25 @@ identifier REL1 =~ "^strbuf_release$";
 // ... or "struct STRBUF buf = STRBUF_INIT;" ...
 |
 - T I = INIT_MACRO;
+|
+// ... or "struct strbuf *buf = xmalloc(...)" etc. ...
+- T I = MALLOC1(...);
 )
 
 // ... Optionally followed by lines that make no use of "buf", "&buf"
 // etc., but which ...
 <... when != \( I \| &I \)
      when strict
+(
 // .. (only) make use of "buf" or "&buf" to call something like
 // "strbuf_init(&buf, ...)" ...
 - \( INIT_CALL1 \)( \( I \| &I \), ...);
+|
+// .. 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) ...
+- I = MALLOC1(...);
+)
 ...>
 
 // ... and then no mention of "buf" or "&buf" until we get to a
-- 
2.37.0.900.g4d0de1cceb2