checkpatch: make "return is not a function" test quieter

This test is a bit noisy and opinions seem to agree that it should not
warn in a lot more situations.

It seems people agree that:

	return (foo || bar);
and
	return foo || bar;

are both acceptable style and checkpatch should be silent about them.

For now, it warns on parentheses around a simple constant or a single
function or a ternary.

	return (foo);
	return (foo(bar));
	return (foo ? bar : baz);

The last ternary test may be quieted in the future.

Modify the deparenthesize function to only strip balanced leading and
trailing parentheses.
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Cc: Monam Agarwal <monamagarwal123@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -439,9 +439,14 @@ our $FuncArg = qr{$Typecast{0,1}($LvalOrFunc|$Constant)};
 sub deparenthesize {
 	my ($string) = @_;
 	return "" if (!defined($string));
-	$string =~ s@^\s*\(\s*@@g;
-	$string =~ s@\s*\)\s*$@@g;
+
+	while ($string =~ /^\s*\(.*\)\s*$/) {
+		$string =~ s@^\s*\(\s*@@;
+		$string =~ s@\s*\)\s*$@@;
+	}
+
 	$string =~ s@\s+@ @g;
+
 	return $string;
 }
 
@@ -3374,14 +3379,17 @@ sub process {
 			}
 		}
 
-# Return is not a function.
+# return is not a function
 		if (defined($stat) && $stat =~ /^.\s*return(\s*)\(/s) {
 			my $spacing = $1;
 			if ($^V && $^V ge 5.10.0 &&
-			    $stat =~ /^.\s*return\s*$balanced_parens\s*;\s*$/) {
+			    $stat =~ /^.\s*return\s*($balanced_parens)\s*;\s*$/) {
+				my $value = $1;
+				$value = deparenthesize($value);
+				if ($value =~ m/^\s*$FuncArg\s*(?:\?|$)/) {
 					ERROR("RETURN_PARENTHESES",
 					      "return is not a function, parentheses are not required\n" . $herecurr);
-
+				}
 			} elsif ($spacing !~ /\s+/) {
 				ERROR("SPACING",
 				      "space required before the open parenthesis '('\n" . $herecurr);