checkpatch: add constant comparison on left side test

"CONST <comparison> variable" checks like:

        if (NULL != foo)
and
        while (0 < bar(...))

where a constant (or what appears to be a constant like an upper case
identifier) is on the left of a comparison are generally preferred to be
written using the constant on the right side like:

        if (foo != NULL)
and
        while (bar(...) > 0)

Add a test for this.

Add a --fix option too, but only do it when the code is immediately
surrounded by parentheses to avoid misfixing things like "(0 < bar() +
constant)"

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Nicolas Morey Chaisemartin <nmorey@kalray.eu>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 97ee377c4f51..f2a1131b2f8b 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4231,6 +4231,35 @@ sub process {
                         }
                 }
 
+# comparisons with a constant or upper case identifier on the left
+#       avoid cases like "foo + BAR < baz"
+#       only fix matches surrounded by parentheses to avoid incorrect
+#       conversions like "FOO < baz() + 5" being "misfixed" to "baz() > FOO + 5"
+                if ($^V && $^V ge 5.10.0 &&
+                    $line =~ /^\+(.*)\b($Constant|[A-Z_][A-Z0-9_]*)\s*($Compare)\s*($LvalOrFunc)/) {
+                        my $lead = $1;
+                        my $const = $2;
+                        my $comp = $3;
+                        my $to = $4;
+                        my $newcomp = $comp;
+                        if ($lead !~ /$Operators\s*$/ &&
+                            $to !~ /^(?:Constant|[A-Z_][A-Z0-9_]*)$/ &&
+                            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;