linux-kernel - coccinelle: Convert comma to semicolons (was Re: [PATCH] checkpatch: Add test for comma use that should be semicolon)

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Date:   Wed, 19 Aug 2020 16:07:23 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Julia Lawall <julia.lawall@...6.fr>,
        cocci <cocci@...teme.lip6.fr>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Whitcroft <apw@...dowen.org>,
        Giuseppe Scrivano <gscrivan@...hat.com>
Subject: coccinelle: Convert comma to semicolons (was Re: [PATCH]
 checkpatch: Add test for comma use that should be semicolon)

On Wed, 2020-08-19 at 14:22 -0700, Joe Perches wrote:
> There are commas used as statement terminations that should typically
> have used semicolons instead.  Only direct assignments or use of a single
> function or value on a single line are detected by this test.
> 
> e.g.:
> 	foo = bar(),		/* typical use is semicolon not comma */
> 	bar = baz();
> 
> Add an imperfect test to detect these comma uses.
> 
> No false positives were found in testing, but many types of false negatives
> are possible.
> 
> e.g.:
> 	foo = bar() + 1,	/* comma use, but not direct assignment */
> 	bar = baz();

Hi.

I recently added a test for this condition to linux's checkpatch.

A similar coccinelle script might be:

$ cat comma.cocci
@@
expression e1;
expression e2;
@@

	e1
-	,
+	;
	e2;
$

This works reasonably well but it has several false positives
for declarations like:

$ spatch --sp-file comma.cocci mm/huge_memory.c
diff -u -p a/huge_memory.c b/huge_memory.c
--- a/huge_memory.c
+++ b/huge_memory.c
@@ -2778,7 +2778,7 @@ static unsigned long deferred_split_scan
 	struct pglist_data *pgdata = NODE_DATA(sc->nid);
 	struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
 	unsigned long flags;
-	LIST_HEAD(list), *pos, *next;
+	LIST_HEAD(list), *pos; *next;
 	struct page *page;
 	int split = 0;
$

Any script improvement suggestions?