From: Joe Perches <email@example.com> To: Andy Whitcroft <firstname.lastname@example.org> Cc: Andrew Morton <email@example.com>, LKML <firstname.lastname@example.org>, Jacob Pan <email@example.com> Subject: Re: [PATCH] checkpatch: Warn on comparisons to true and false Date: Wed, 10 Apr 2013 04:27:51 -0700 [thread overview] Message-ID: <1365593271.27174.35.camel@joe-AO722> (raw) In-Reply-To: <20130410093346.GO7511@dm> On Wed, 2013-04-10 at 10:33 +0100, Andy Whitcroft wrote: > On Tue, Apr 09, 2013 at 08:17:14PM -0700, Joe Perches wrote: > > Comparisons of A to true and false are better written > > as A and !A.  > In a complex case such as a + b == false will this do the right thing? Very sensible question. No it won't. checkpatch doesn't understand expressions very well nor does it understand precedence operations between expressions and tests. I did run it against the kernel tree and there weren't any I noticed like that though. > Not that I am sure that adding bools makes sense but assuming there is > some valid complex lval. $Lval in this case is a single variable and is neither a function nor an expression. It doesn't match on: if (func(x, y) == true) or if ((x | y) == true) because of the ) before the == It will falsely match on expressions like: if (x + y == true) but as far as I can tell there aren't any uses like that in the kernel tree. $ git grep -E "(==|\!=)\s*(true|false)\b" | \ cut -f2- -d":" |grep -P "\b(\+|\-)\b" nor are there any and/or bit operator. When I tried adding a test for: "$Constant == $Lval" instead of "$Lval == $Constant" like 0 == foo instead of foo == 0 there were _way_ too many false positives of the $Expression sort that I didn't add that test. cheers, Joe
next prev parent reply other threads:[~2013-04-10 11:27 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-04-10 3:17 Joe Perches 2013-04-10 9:33 ` Andy Whitcroft 2013-04-10 11:27 ` Joe Perches [this message] 2013-04-10 12:41 ` Andy Whitcroft 2013-04-10 22:57 ` Andrew Morton 2013-04-11 1:07 ` Joe Perches 2013-04-11 2:14 ` Dave Jones 2013-04-11 3:47 ` Joe Perches 2013-04-11 8:19 ` Dan Carpenter 2013-04-11 8:29 ` Joe Perches 2013-04-11 11:56 ` Bjørn Mork 2013-04-11 14:25 ` Joe Perches
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