added existence chains with '?.' -- soaks up attempts to access undefined properties, returning 'undefined'

lib/coffee_script/grammar.y

@@ -4,7 +4,7 @@ class Parser
 token IF ELSE UNLESS
 token NUMBER STRING REGEX
 token TRUE FALSE YES NO ON OFF
-token IDENTIFIER PROPERTY_ACCESS PROTOTYPE_ACCESS
+token IDENTIFIER PROPERTY_ACCESS PROTOTYPE_ACCESS SOAK_ACCESS
 token CODE PARAM NEW RETURN
 token TRY CATCH FINALLY THROW
 token BREAK CONTINUE
@@ -242,7 +242,8 @@ rule
   # Accessing into an object or array, through dot or index notation.
   Accessor:
     PROPERTY_ACCESS IDENTIFIER        { result = AccessorNode.new(val[1]) }
-  | PROTOTYPE_ACCESS IDENTIFIER       { result = AccessorNode.new(val[1], true) }
+  | PROTOTYPE_ACCESS IDENTIFIER       { result = AccessorNode.new(val[1], :prototype) }
+  | SOAK_ACCESS IDENTIFIER            { result = AccessorNode.new(val[1], :soak) }
   | Index                             { result = val[0] }
   | Range                             { result = SliceNode.new(val[0]) }
   ;

lib/coffee_script/lexer.rb

@@ -91,8 +91,15 @@ module CoffeeScript
       # 'if' will result in an [:IF, "if"] token.
       tag = KEYWORDS.include?(identifier) ? identifier.upcase.to_sym : :IDENTIFIER
       tag = :LEADING_WHEN if tag == :WHEN && [:OUTDENT, :INDENT, "\n"].include?(last_tag)
-      @tokens[-1][0] = :PROPERTY_ACCESS if tag == :IDENTIFIER && last_value == '.' && !(@tokens[-2] && @tokens[-2][1] == '.')
       @tokens[-1][0] = :PROTOTYPE_ACCESS if tag == :IDENTIFIER && last_value == '::'
+      if tag == :IDENTIFIER && last_value == '.' && !(@tokens[-2] && @tokens[-2][1] == '.')
+        if @tokens[-2][0] == "?"
+          @tokens[-1][0] = :SOAK_ACCESS
+          @tokens.delete_at(-2)
+        else
+          @tokens[-1][0] = :PROPERTY_ACCESS
+        end
+      end
       token(tag, identifier)
       @i += identifier.length
     end

lib/coffee_script/nodes.rb

@@ -333,7 +333,7 @@ module CoffeeScript
     attr_reader :last, :source
 
     def initialize(base, properties=[])
-      @base, @properties = base, properties
+      @base, @properties = base, [properties].flatten
     end
 
     def <<(other)
@@ -367,12 +367,23 @@ module CoffeeScript
     end
 
     def compile_node(o)
-      only  = o.delete(:only_first)
-      props = only ? @properties[0...-1] : @properties
-      parts = [@base, props].flatten.map {|val| val.compile(o) }
+      soaked    = false
+      only      = o.delete(:only_first)
+      props     = only ? @properties[0...-1] : @properties
+      baseline  = @base.compile(o)
+      parts     = [baseline.dup]
+      props.each do |prop|
+        if prop.is_a?(AccessorNode) && prop.soak
+          soaked = true
+          parts[-1] << " == undefined ? undefined : #{baseline += prop.compile(o)}"
+        else
+          parts << prop.compile(o)
+        end
+      end
       @last = parts.last
       @source = parts.length > 1 ? parts[0...-1].join('') : nil
-      write(parts.join(''))
+      code = parts.join('')
+      write(soaked ? "(#{code})" : code)
     end
   end
 
@@ -380,9 +391,12 @@ module CoffeeScript
   # an accessor into the object's prototype.
   class AccessorNode < Node
     children :name
+    attr_reader :soak
 
-    def initialize(name, prototype=false)
-      @name, @prototype = name, prototype
+    def initialize(name, tag=nil)
+      @name       = name
+      @prototype  = tag == :prototype
+      @soak       = tag == :soak
     end
 
     def compile_node(o)

test/fixtures/execution/test_existence.coffee

@@ -30,4 +30,15 @@ get_next_node: =>
   throw "up" if counter
   counter++
 
-print(if get_next_node()? then true else false)
+print(if get_next_node()? then true else false)
+
+
+# Existence chains, soaking up undefined properties:
+
+obj: {
+  prop: "hello"
+}
+
+print(obj?.prop is "hello")
+
+print(obj?.prop?.non?.existent?.property is undefined)