Do something sensible about uninspectable things

lib/pry.rb

@@ -19,11 +19,21 @@ class Pry
 
   # The default prints
   DEFAULT_PRINT = proc do |output, value|
-    begin
-      Helpers::BaseHelpers.stagger_output("=> #{Helpers::BaseHelpers.colorize_code(value.pretty_inspect)}", output)
-    rescue NoMethodError
-      output.puts "=> unknown"
+    stringified = begin
+                    value.pretty_inspect
+                  rescue Exception => ex
+                    nil
+                  end
+
+    unless String === stringified
+      # Read the class name off of the singleton class to provide a default inspect.
+      klass = (class << value; self; end).ancestors.first
+      stringified = "#<#{klass}:0x#{value.__id__.to_s(16)}>"
+      warning = "output error: #{ex ? ex.inspect : ".pretty_inspect didn't return a String"}"
+      Helpers::BaseHelpers.stagger_output(warning, output)
     end
+
+    Helpers::BaseHelpers.stagger_output("=> #{Helpers::BaseHelpers.colorize_code(stringified)}", output)
   end
 
   # Will only show the first line of the backtrace

test/test_pry_output.rb

@@ -27,4 +27,22 @@ describe Pry do
       mock_pry("1").should =~ /output error: failed to show result/
     end
   end
+
+  describe "DEFAULT_PRINT" do
+    it "should output the right thing" do
+      mock_pry("{:a => 1}").should =~ /\{:a=>1\}/
+    end
+
+    it "should not be phased by un-inspectable things" do
+      mock_pry("class NastyClass; undef pretty_inspect; end", "NastyClass.new").should =~ /#<NastyClass:0x[0-9a-f]+>/
+    end
+
+    it "should warn you about un-inspectable things" do
+      mock_pry("class NastyClass; undef pretty_inspect; end", "NastyClass.new").should =~ /output error: #<(NoMethodError|NameError): undefined method `pretty_inspect'/
+    end
+
+    it "should warn you when you have badly behaved objects" do
+      mock_pry("class UnCouth; def pretty_inspect(*a); :cussing_symbol; end; end", "UnCouth.new").should =~ /output error: .pretty_inspect didn't return a String/
+    end
+  end
 end