[PATCH V2] checkpatch: Warn on unnecessary void function return statements

[Joe Perches]

With some exceptions, warn on void functions that end with a
"return;", because it's unnecessary.

Check the closing brace at the start of a line.
If the line before that has a single tab, then return;
look at the line before that.  If it's not a label,
emit a warning.

So, emit a warning on:

void function(...)
{
	[...]
	return;
}

but do not emit a warning on the below because
gcc requires any statement (including a bare
semicolon) before the closing function brace:

void function(...)
{
	[...]
		goto label;
	[...]

label:
	return;
}

Signed-off-by: Joe Perches <joe@xxxxxxxxxxx>
---

V2: The previous patch had a few too many false positives
    on styles that should be acceptable.

 scripts/checkpatch.pl | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 862cc7a..b191c88 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3470,6 +3470,18 @@ sub process {
 			}
 		}
 
+# unnecessary return in a void function
+# at end-of-function, with the previous line a single leading tab, then return;
+# and the line before that not a goto label target like "out:"
+		if ($sline =~ /^[ \+]}\s*$/ &&
+		    $prevline =~ /^\+\treturn\s*;\s*$/ &&
+		    $linenr >= 3 &&
+		    $lines[$linenr - 3] =~ /^[ +]/ &&
+		    $lines[$linenr - 3] !~ /^[ +]\s*$Ident\s*:/) {
+			WARN("RETURN_VOID",
+			     "void function return statements are not generally useful\n" . $hereprev);
+               }
+
 # if statements using unnecessary parentheses - ie: if ((foo == bar))
 		if ($^V && $^V ge 5.10.0 &&
 		    $line =~ /\bif\s*((?:\(\s*){2,})/) {


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