Refactor binary operation node pattern matching code to improve readability.

Also handle cases where the if-statement's condition is not a `DropTemps` expression.

Author: Arc8ne

clippy_lints/src/collapsible_if.rs

@@ -99,13 +99,10 @@ fn check_collapsible_if_nested_if_else(cx: &LateContext<'_>, if_expr: &Expr<'_>)
                                 ExprKind::Binary(bin_op, lhs, rhs) => {
                                     let new_bin_op;
 
-                                    match bin_op.node {
-                                        BinOpKind::Ne => {
-                                            new_bin_op = BinOpKind::Eq;
-                                        },
-                                        _ => {
-                                            new_bin_op = BinOpKind::Ne;
-                                        },
+                                    if let BinOpKind::Ne = bin_op.node {
+                                        new_bin_op = BinOpKind::Eq;
+                                    } else {
+                                        new_bin_op = BinOpKind::Ne;
                                     }
 
                                     cond_sugg =
@@ -121,6 +118,8 @@ fn check_collapsible_if_nested_if_else(cx: &LateContext<'_>, if_expr: &Expr<'_>)
                                 },
                                 _ => {},
                             }
+                        } else {
+                            cond_sugg = make_unop("!", Sugg::hir(cx, cond, ".."));
                         }
 
                         span_lint_and_then(