Build no_effect suggestion only when necessary

Author: mcarton

clippy_lints/src/no_effect.rs

@@ -92,19 +92,20 @@ impl LateLintPass for Pass {
             if has_no_effect(cx, expr) {
                 span_lint(cx, NO_EFFECT, stmt.span, "statement with no effect");
             } else if let Some(reduced) = reduce_expression(cx, expr) {
-                let mut snippet = String::new();
-                for e in reduced {
-                    if in_macro(cx, e.span) {
-                        return;
-                    }
-                    if let Some(snip) = snippet_opt(cx, e.span) {
-                        snippet.push_str(&snip);
-                        snippet.push(';');
-                    } else {
-                        return;
-                    }
-                }
                 span_lint_and_then(cx, UNNECESSARY_OPERATION, stmt.span, "statement can be reduced", |db| {
+                    let mut snippet = String::new();
+                    for e in reduced {
+                        if in_macro(cx, e.span) {
+                            return;
+                        }
+                        if let Some(snip) = snippet_opt(cx, e.span) {
+                            snippet.push_str(&snip);
+                            snippet.push(';');
+                        } else {
+                            return;
+                        }
+                    }
+
                     db.span_suggestion(stmt.span, "replace it with", snippet);
                 });
             }