Fixes #2508 -- existential access of the prototype.

Author: jashkenas

lib/coffee-script/grammar.js

@@ -263,7 +263,8 @@ grammar =
   Accessor: [
     o '.  Identifier',                          -> new Access $2
     o '?. Identifier',                          -> new Access $2, 'soak'
-    o ':: Identifier',                          -> [LOC(1)(new Access new Literal 'prototype'), LOC(2)(new Access $2)]
+    o ':: Identifier',                          -> [LOC(1)(new Access new Literal('prototype')), LOC(2)(new Access $2)]
+    o '?:: Identifier',                         -> [LOC(1)(new Access new Literal('prototype'), 'soak'), LOC(2)(new Access $2)]
     o '::',                                     -> new Access new Literal 'prototype'
     o 'Index'
   ]
@@ -576,7 +577,7 @@ grammar =
 #
 #     (2 + 3) * 4
 operators = [
-  ['left',      '.', '?.', '::']
+  ['left',      '.', '?.', '::', '?::']
   ['left',      'CALL_START', 'CALL_END']
   ['nonassoc',  '++', '--']
   ['left',      '?']

lib/coffee-script/lexer.js

@@ -114,7 +114,7 @@ exports.Lexer = class Lexer
       @token 'OWN', id
       return id.length
     forcedIdentifier = colon or
-      (prev = last @tokens) and (prev[0] in ['.', '?.', '::'] or
+      (prev = last @tokens) and (prev[0] in ['.', '?.', '::', '?::'] or
       not prev.spaced and prev[0] is '@')
     tag = 'IDENTIFIER'
 
@@ -678,7 +678,7 @@ exports.Lexer = class Lexer
   # Are we in the midst of an unfinished expression?
   unfinished: ->
     LINE_CONTINUER.test(@chunk) or
-    @tag() in ['\\', '.', '?.', 'UNARY', 'MATH', '+', '-', 'SHIFT', 'RELATION'
+    @tag() in ['\\', '.', '?.', '?::', 'UNARY', 'MATH', '+', '-', 'SHIFT', 'RELATION'
                'COMPARE', 'LOGIC', 'THROW', 'EXTENDS']
 
   # Converts newlines for string literals.
@@ -771,7 +771,7 @@ OPERATOR   = /// ^ (
    | >>>=?             # zero-fill right shift
    | ([-+:])\1         # doubles
    | ([&|<>])\2=?      # logic / shift
-   | \?\.              # soak access
+   | \?(\.|::)         # soak access
    | \.{2,3}           # range or splat
 ) ///
 

lib/coffee-script/parser.js

@@ -270,7 +270,7 @@ class exports.Rewriter
       # .g b, ->
       #   c
       # .h a
-      if prevTag is 'OUTDENT' and inImplicitCall() and tag in ['.', '?.', '::']
+      if prevTag is 'OUTDENT' and inImplicitCall() and tag in ['.', '?.', '::', '?::']
         endImplicitCall()
         return forward(1)
 

lib/coffee-script/rewriter.js

@@ -293,4 +293,6 @@ test "#2567: Optimization of negated existential produces correct result", ->
   ok !(!a?)
   ok !b?
 
-
+test "#2508: Existential access of the prototype", ->
+  eq NonExistent?::nothing, undefined
+  ok Object?::toString