fix corner cases in arrow functions & rests (#4667)

fixes #4666

lib/compress.js

@@ -762,10 +762,11 @@ merge(Compressor.prototype, {
                     return arg || make_node(AST_Undefined, iife);
                 }, visit);
             });
-            if (fn.rest) scan_declaration(tw, compressor, fn.rest, compressor.option("rests") && function() {
-                return make_node(AST_Array, fn, {
+            var rest = fn.rest;
+            if (rest) scan_declaration(tw, compressor, rest, compressor.option("rests") && function() {
+                return fn.rest === rest ? make_node(AST_Array, fn, {
                     elements: iife.args.slice(fn.argnames.length),
-                });
+                }) : rest;
             }, visit);
             walk_lambda(fn, tw);
             var safe_ids = tw.safe_ids;

lib/parse.js

@@ -1198,6 +1198,7 @@ function parse($TEXT, options) {
             }
         } else {
             body = [];
+            handle_regexp();
             value = maybe_assign();
         }
         S.input.pop_directives_stack();