linux-kernel - [PATCH v3 1/1] checkpatch: don't suggest else is not useful with chained if blocks

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Message-ID: <e14d1c82-775d-58ec-11f9-4f2771111fc3@linux.intel.com>
Date:   Mon, 21 Mar 2022 17:39:18 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Joe Perches <joe@...ches.com>
cc:     Andy Whitcroft <apw@...onical.com>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v3 1/1] checkpatch: don't suggest else is not useful with
 chained if blocks

When if blocks are chained with "else if" like this:

	if (a)
		c = 0;
	else if (b)
		break;
	else
		c = 1;

checkpatch recommends removing else:

WARNING: else is not generally useful after a break or return

Removing else will easily introduce logic errors in this situation
so it's better to check if the preceding line has "else if" before
issuing that warning.

Fixes: 032a4c0f9a77 ("checkpatch: warn on unnecessary else after return or break")
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
---

v2:
- Don't match spuriously to removed lines
- Extend check backwards to the first line with the same or lower indent 
  as "else" line

v3:
- Add back the check to ensure line is defined

 scripts/checkpatch.pl | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index b01c36a15d9d..3ea73155c42b 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4037,14 +4037,24 @@ sub process {
 # check indentation of any line with a bare else
 # (but not if it is a multiple line "if (foo) return bar; else return baz;")
 # if the previous line is a break or return and is indented 1 tab more...
+# but don't warn when there is "else if" before that line to avoid logic errors
 		if ($sline =~ /^\+([\t]+)(?:}[ \t]*)?else(?:[ \t]*{)?\s*$/) {
 			my $tabs = length($1) + 1;
 			if ($prevline =~ /^\+\t{$tabs,$tabs}break\b/ ||
 			    ($prevline =~ /^\+\t{$tabs,$tabs}return\b/ &&
 			     defined $lines[$linenr] &&
 			     $lines[$linenr] !~ /^[ \+]\t{$tabs,$tabs}return/)) {
-				WARN("UNNECESSARY_ELSE",
-				     "else is not generally useful after a break or return\n" . $hereprev);
+				my $ifline = $linenr - 3;
+				$tabs--;
+				while ($ifline >= 1 &&
+				       $lines[$ifline] !~ /^[^-]\t{0,$tabs}[^\t]/) {
+					$ifline--;
+				}
+				if (!defined $lines[$ifline] ||
+				    $lines[$ifline] !~ /^[\+ ]\t{$tabs,$tabs}(\} *|)else if\s*\(/) {
+					WARN("UNNECESSARY_ELSE",
+					     "else is not generally useful after a break or return\n" . $hereprev);
+				}
 			}
 		}
 
-- 
2.30.2