Re: [PATCH] checkpatch: add --strict "pointer comparison to NULL" test

[Joe Perches <joe@perches.com>]

On Thu, 2015-08-27 at 07:49 +0530, Viresh Kumar wrote:
> Few colleagues asked me why isn't checkpatch warning for (NULL == ptr)
> or (NULL != ptr) checks, as it warns for (ptr == NULL) and (ptr != NULL).
> 
> Did you miss it? or was it intentional ?

I didn't miss it.

NULL == foo is relatively unusual and not really worth the
bother.

And because most likely, "CONST test variable" checks like
	NULL != foo
and
	0 < bar

should probably be a separate test.

Something like:
---
 scripts/checkpatch.pl | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index e14dcdb..457ddef 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4231,6 +4231,29 @@ sub process {
 			}
 		}
 
+# comparisons with a constant on the left
+		if ($^V && $^V ge 5.10.0 &&
+		    $line =~ /\b($Constant|[A-Z_]+)\s*($Compare)\s*($LvalOrFunc)/) {
+			my $const = $1;
+			my $comp = $2;
+			my $to = $3;
+			my $newcomp = $comp;
+			if (WARN("CONSTANT_COMPARISON",
+				 "Comparisons should place the constant on the right side of the test\n" . $herecurr) &&
+			    $fix) {
+				if ($comp eq "<") {
+					$newcomp = ">=";
+				} elsif ($comp eq "<=") {
+					$newcomp = ">";
+				} elsif ($comp eq ">") {
+					$newcomp = "<=";
+				} elsif ($comp eq ">=") {
+					$newcomp = "<";
+				}
+				$fixed[$fixlinenr] =~ s/\(\s*\Q$const\E\s*$Compare\s*\Q$to\E\s*\)/($to $newcomp $const)/;
+			}
+		}
+
 # Return of what appears to be an errno should normally be negative
 		if ($sline =~ /\breturn(?:\s*\(+\s*|\s+)(E[A-Z]+)(?:\s*\)+\s*|\s*)[;:,]/) {
 			my $name = $1;