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

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Date:	Wed, 24 Jul 2013 19:59:10 -0700
From:	Joe Perches <joe@...ches.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andy Whitcroft <apw@...onical.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Cong Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH] checkpatch: Warn when using extern with function prototypes
 in .h files

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@...essinduktion.org>
Signed-off-by: Joe Perches <joe@...ches.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@...ches.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



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