[PATCH] checkpatch: Warn when using extern with function prototypes in .h files

[Joe Perches <joe@perches.com>]

Using the extern keyword on function prototypes is superfluous
visual noise so suggest removing it.

Using extern can cause unnecessary line wrapping at 80 columns
and unnecessarily long multi-line function prototypes.

Suggested-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Joe Perches <joe@perches.com>
---
On Thu, 2013-07-25 at 03:47 +0200, Hannes Frederic Sowa wrote:
> On Wed, Jul 24, 2013 at 06:41:20PM -0700, Joe Perches wrote:
> > On Thu, 2013-07-25 at 01:27 +0000, Cong Wang wrote:
> > > On Tue, 23 Jul 2013 at 17:58 GMT, Joe Perches <joe@perches.com> wrote:
> > > > Function prototypes don't need to be declared
> > > > extern in .h files.  It's assumed by the compiler
> > > > and is as unnecessary as using auto is when
> > > > declaring automatic/local variables in a block.
> > > Since we all know this, why bother it?
> > If everyone knew this, new ones wouldn't be added.
> > But a lot are.
> Couldn't checkpatch take care of these?

checkpatch doesn't work well for multiple lines so
this doesn't work on things like
	extern unsigned long
	foo(type bar);
but it does for the single line function prototypes.

Using --fix removes them.

 scripts/checkpatch.pl | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 6918517..23126d4 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3866,6 +3866,16 @@ sub process {
 			}
 		}
 
+# check for new externs in .h files.
+		if ($realfile =~ /\.h$/ &&
+		    $line =~ /^\+\s*(extern\s+)$Type\s*$Ident\s*\(/s) {
+			if (WARN("AVOID_EXTERNS",
+				 "extern prototypes should be avoided in .h files\n" . $herecurr) &&
+			    $fix) {
+				$fixed[$linenr - 1] =~ s/(.*)\bextern\b\s*(.*)/$1$2/;
+			}
+		}
+
 # check for new externs in .c files.
 		if ($realfile =~ /\.c$/ && defined $stat &&
 		    $stat =~ /^.\s*(?:extern\s+)?$Type\s+($Ident)(\s*)\(/s)
-- 
1.8.1.2.459.gbcd45b4.dirty