Use suggestion for redundant_closure

src/utils.rs

@@ -195,6 +195,11 @@ pub fn snippet<'a, T: LintContext>(cx: &T, span: Span, default: &'a str) -> Cow<
     cx.sess().codemap().span_to_snippet(span).map(From::from).unwrap_or(Cow::Borrowed(default))
 }
 
+/// Converts a span to a code snippet. Returns None if not available.
+pub fn snippet_opt<T: LintContext>(cx: &T, span: Span) -> Option<String> {
+    cx.sess().codemap().span_to_snippet(span).ok()
+}
+
 /// convert a span (from a block) to a code snippet if available, otherwise use default, e.g.
 /// `snippet(cx, expr.span, "..")`
 /// This trims the code of indentation, except for the first line