Fix `isLiteralArguments`

`isLiteralArguments` mistakenly looked at `Literal`s instead of
`IdentifierLiteral`s.

This also gets rid of the ugly `.asKey` hack in nodes.coffee.

Fixes #4320.

lib/coffee-script/nodes.js

@@ -1241,7 +1241,6 @@
 
     function Access(name1, tag) {
       this.name = name1;
-      this.name.asKey = true;
       this.soak = tag === 'soak';
     }
 
@@ -1483,7 +1482,6 @@
             if (!(prop instanceof Assign)) {
               prop = new Assign(prop, prop, 'object');
             }
-            (prop.variable.base || prop.variable).asKey = true;
           } else {
             if (prop instanceof Assign) {
               key = prop.variable;
@@ -3779,11 +3777,11 @@
   };
 
   isLiteralArguments = function(node) {
-    return node instanceof Literal && node.value === 'arguments' && !node.asKey;
+    return node instanceof IdentifierLiteral && node.value === 'arguments';
   };
 
   isLiteralThis = function(node) {
-    return (node instanceof ThisLiteral && !node.asKey) || (node instanceof Code && node.bound) || node instanceof SuperCall;
+    return node instanceof ThisLiteral || (node instanceof Code && node.bound) || node instanceof SuperCall;
   };
 
   isComplexOrAssignable = function(node) {

src/nodes.coffee

@@ -807,7 +807,6 @@ exports.Extends = class Extends extends Base
 # an access into the object's prototype.
 exports.Access = class Access extends Base
   constructor: (@name, tag) ->
-    @name.asKey = yes
     @soak  = tag is 'soak'
 
   children: ['name']
@@ -1014,7 +1013,6 @@ exports.Obj = class Obj extends Base
         if i < dynamicIndex
           if prop not instanceof Assign
             prop = new Assign prop, prop, 'object'
-          (prop.variable.base or prop.variable).asKey = yes
         else
           if prop instanceof Assign
             key = prop.variable
@@ -2561,10 +2559,10 @@ multident = (code, tab) ->
   code.replace /\s+$/, ''
 
 isLiteralArguments = (node) ->
-  node instanceof Literal and node.value is 'arguments' and not node.asKey
+  node instanceof IdentifierLiteral and node.value is 'arguments'
 
 isLiteralThis = (node) ->
-  (node instanceof ThisLiteral and not node.asKey) or
+  node instanceof ThisLiteral or
     (node instanceof Code and node.bound) or
     node instanceof SuperCall
 

test/classes.coffee

@@ -712,6 +712,11 @@ test "#2630: class bodies can't reference arguments", ->
   throws ->
     CoffeeScript.compile('class Test then arguments')
 
+  # #4320: Don't be too eager when checking, though.
+  class Test
+    arguments: 5
+  eq 5, Test::arguments
+
 test "#2319: fn class n extends o.p [INDENT] x = 123", ->
   first = ->