[PATCH v2] checkpatch: exclude forward declarations of const structs

[Taylor Nelms]

Limit checkpatch warnings for normally-const structs by excluding
patterns consistent with forward declarations.

For example, the forward declaration `struct regmap_access_table;` in a
header file currently generates a warning recommending that it is
generally declared as const; however, this would apply a useless type
qualifier in the empty declaration `const struct regmap_access_table;`,
and subsequently generate compiler warnings.

Signed-off-by: Taylor Nelms <tknelms@xxxxxxxxxx>
---

Changelog since v1:
- Changed capturing group to character class in regex.

 scripts/checkpatch.pl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index e56374662ff7..bed0bfedf5ba 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -7502,10 +7502,10 @@ sub process {
 		}
 
 # check for various structs that are normally const (ops, kgdb, device_tree)
-# and avoid what seem like struct definitions 'struct foo {'
+# and avoid what seem like struct definitions 'struct foo {' or forward declarations 'struct foo;'
 		if (defined($const_structs) &&
 		    $line !~ /\bconst\b/ &&
-		    $line =~ /\bstruct\s+($const_structs)\b(?!\s*\{)/) {
+		    $line =~ /\bstruct\s+($const_structs)\b(?!\s*[\{;])/) {
 			WARN("CONST_STRUCT",
 			     "struct $1 should normally be const\n" . $herecurr);
 		}
-- 
2.53.0.1118.gaef5881109-goog