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

[Joe Perches <joe@perches.com>]

It seems there are more and more uses of "if (!ptr)"
in preference to "if (ptr == NULL)" so add a --strict
test to emit a message when using the latter form.

This also finds (ptr != NULL).

Fix it too if desired.

Signed-off-by: Joe Perches <joe@perches.com>
---
Seeing no objections, so submitting it.

 scripts/checkpatch.pl | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 24d6702..d4e08bc 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4490,6 +4490,20 @@ sub process {
 			     "Possible precedence defect with mask then right shift - may need parentheses\n" . $herecurr);
 		}
 
+# check for pointer comparisons to NULL
+		if ($^V && $^V ge 5.10.0) {
+			while ($line =~ /\b$LvalOrFunc\s*(==|\!=)\s*NULL\b/g) {
+				my $val = $1;
+				my $equal = "!";
+				$equal = "" if ($4 eq "!=");
+				if (CHK("COMPARISON_TO_NULL",
+					"Comparison to NULL could be written \"${equal}${val}\"\n" . $herecurr) &&
+					    $fix) {
+					$fixed[$fixlinenr] =~ s/\b\Q$val\E\s*(?:==|\!=)\s*NULL\b/$equal$val/;
+				}
+			}
+		}
+
 # check for bad placement of section $InitAttribute (e.g.: __initdata)
 		if ($line =~ /(\b$InitAttribute\b)/) {
 			my $attr = $1;