Allow customisation of the prompt objects

Fix issue pry#885 (Add an API for extending Pry.view_clip)

    [1] pry(main)> class Barbie
                 |   def inspect
                 |     'You can brush my hair, undress me everywhere!'
                 |   end
                 | end
    => nil
    [2] pry(main)>
    [3] pry(main)> Pry.config.prompt_safe_objects << Barbie
    => [String, Numeric, Symbol, nil, true, false, Barbie]
    [4] pry(main)> cd Barbie.new
    [5] pry(You can brush my hair, undress me everywhere!):1>

lib/pry.rb

@@ -90,6 +90,8 @@ def self.output_with_default_format(output, value, options = {})
                     }
                    ]
 
+  DEFAULT_PROMPT_SAFE_OBJECTS = [String, Numeric, Symbol, nil, true, false]
+
   # A simple prompt - doesn't display target or nesting level
   SIMPLE_PROMPT = [proc { ">> " }, proc { " | " }]
 

lib/pry/config.rb

@@ -119,6 +119,20 @@ def hooks=(v)
     #   Pry.config.prompt_name = 'my_rails_project'
     attr_accessor :prompt_name
 
+    # The list of safe objects, the `#inspect` method of which can be used for
+    # the prompt. The default safe objects are defined in
+    # `DEFAULT_PROMPT_SAFE_OBJECTS` (see Pry::DEFAULT_PROMPT_SAFE_OBJECTS).
+    # @return [Array]
+    # @example
+    #   class Barbie
+    #     def inspect
+    #       'You can brush my hair, undress me everywhere!'
+    #     end
+    #   end
+    #
+    #   Pry.config.prompt_safe_objects << Barbie
+    attr_accessor :prompt_safe_objects
+
     # The default editor to use. Defaults to $VISUAL, $EDITOR, or a sensible
     # fallback for the platform. If `editor` is a String then that string is
     # used as the shell command to invoke the editor. If `editor` is callable

lib/pry/pry_class.rb

@@ -184,7 +184,7 @@ def self.view_clip(obj, max_length = 60)
     elsif TOPLEVEL_BINDING.eval('self') == obj
       # special case for 'main' object :)
       obj.to_s
-    elsif [String, Numeric, Symbol, nil, true, false].any? { |v| v === obj } && obj.inspect.length <= max_length
+    elsif Pry.config.prompt_safe_objects.any? { |v| v === obj } && obj.inspect.length <= max_length
       obj.inspect
     else
       "#<#{obj.class}>"#:%x>"# % (obj.object_id << 1)
@@ -280,6 +280,7 @@ def self.set_config_defaults
     config.commands = Pry::Commands
     config.prompt_name = DEFAULT_PROMPT_NAME
     config.prompt = DEFAULT_PROMPT
+    config.prompt_safe_objects = DEFAULT_PROMPT_SAFE_OBJECTS
     config.print = DEFAULT_PRINT
     config.exception_handler = DEFAULT_EXCEPTION_HANDLER
     config.exception_whitelist = DEFAULT_EXCEPTION_WHITELIST

spec/pry_defaults_spec.rb

@@ -263,18 +263,24 @@ def o.inspect; "a" * VC_MAX_LENGTH; end
       end
     end
 
-    describe "given the a Numeric, String or Symbol object" do
+    describe "the list of prompt safe objects" do
       [1, 2.0, -5, "hello", :test].each do |o|
         it "returns the #inspect of the special-cased immediate object: #{o}" do
           Pry.view_clip(o, VC_MAX_LENGTH).should == o.inspect
         end
       end
 
-      # only testing with String here :)
       it "returns #<> format of the special-cased immediate object if #inspect is longer than maximum" do
         o = "o" * (VC_MAX_LENGTH + 1)
         Pry.view_clip(o, VC_MAX_LENGTH).should =~ /#<String/
       end
+
+      it "returns the #inspect of the custom prompt safe objects" do
+        Barbie = Class.new { def inspect; "life is plastic, it's fantastic" end }
+        Pry.config.prompt_safe_objects << Barbie
+        output = Pry.view_clip(Barbie.new, VC_MAX_LENGTH)
+        output.should == "life is plastic, it's fantastic"
+      end
     end
 
     describe "given an object with an #inspect string as long as the maximum specified" do