support local variable and method fallback contexts

lib/docile.rb

@@ -1,9 +1,11 @@
 require "docile/version"
+require "docile/fallback_context_proxy"
 
 module Docile
   # Executes a block in the context of an object whose interface represents a DSL.
   #
-  #   Docile.dsl_eval([]) do
+  # Example of using an Array as a DSL:
+  #   Docile.dsl_eval [] do
   #     push 1
   #     push 2
   #     pop
@@ -16,7 +18,7 @@ module Docile
   # @return [Object]     the given DSL object
   def dsl_eval(dsl, &block)
     block_context = eval("self", block.binding)
-    dsl.instance_eval(&block)
+    FallbackContextProxy.new(dsl, block_context).instance_eval(&block)
     dsl
   end
   module_function :dsl_eval

lib/docile/fallback_context_proxy.rb

@@ -0,0 +1,43 @@
+require 'set'
+
+module Docile
+  class FallbackContextProxy
+    BASIC_METHODS = Set[:==, :equal?, :"!", :"!=", :instance_eval, :object_id, :__send__, :__id__]
+
+    instance_methods.each do |method|
+      unless BASIC_METHODS.include?(method.to_sym)
+        undef_method(method)
+      end
+    end
+
+    def initialize(receiver, fallback)
+      @__receiver__ = receiver
+      @__fallback__ = fallback
+    end
+
+    def id
+      @__receiver__.__send__(:id)
+    end
+
+    # Special case due to `Kernel#sub`'s existence
+    def sub(*args, &block)
+      __proxy_method__(:sub, *args, &block)
+    end
+
+    def method_missing(method, *args, &block)
+      __proxy_method__(method, *args, &block)
+    end
+
+    def __proxy_method__(method, *args, &block)
+      begin
+        @__receiver__.__send__(method.to_sym, *args, &block)
+      rescue ::NoMethodError => e
+        begin
+          @__fallback__.__send__(method.to_sym, *args, &block)
+        rescue ::NoMethodError
+          raise(e)
+        end
+      end
+    end
+  end
+end

spec/docile_spec.rb

@@ -30,8 +30,7 @@ describe Docile do
       end.should == [1, 3]
     end
 
-    context "methods"
+    context "methods" do
-
       it "should find method of outer dsl in outer dsl scope" do
         outer { a.should == 'a' }
       end
@@ -40,36 +39,44 @@ describe Docile do
         outer { inner { b.should == 'b' } }
       end
 
-      #it "should find method of outer dsl in inner dsl scope" do
+      it "should find method of outer dsl in inner dsl scope" do
-      #  outer { inner { a.should == 'a' } }
+        outer { inner { a.should == 'a' } }
-      #end
-      #
-      #it "should find method of block's context in outer dsl scope" do
-      #  def c; 'c'; end
-      #  outer { c.should == 'c' }
-      #end
-      #
-      #it "should find method of block's context in inner dsl scope" do
-      #  def c; 'c'; end
-      #  outer { inner { c.should == 'c' } }
-      #end
       end
 
-  #  it "should find local variable from block context in outer dsl scope" do
+      it "should find method of block's context in outer dsl scope" do
-  #    foo = 'foo'
+        def c; 'c'; end
-  #    outer { foo.should == 'foo' }
+        outer { c.should == 'c' }
-  #  end
+      end
-  #
+
-  #
+      it "should find method of block's context in inner dsl scope" do
-  #
+        def c; 'c'; end
-  #  it "should find local variable from block definition in inner dsl scope" do
+        outer { inner { c.should == 'c' } }
-  #    bar = 'bar'
+      end
-  #    outer { inner { bar.should == 'bar' } }
+
-  #  end
+      it "should find method of outer dsl in preference to block context" do
-  #
+        def a; 'not a'; end
+        outer { a.should == 'a' }
+      end
+    end
+
+    context "local variables" do
+      it "should find local variable from block context in outer dsl scope" do
+        foo = 'foo'
+        outer { foo.should == 'foo' }
+      end
+
+      it "should find local variable from block definition in inner dsl scope" do
+        bar = 'bar'
+        outer { inner { bar.should == 'bar' } }
+      end
+    end
+
+    context "instance variables" do
       #it "should find instance variable from block definition in inner dsl scope" do
       #  @iv1 = 'iv1'; outer { inner { @iv1.should == 'iv1' } }
       #end
-  #end
+    end
+
+  end
 
 end