Be paranoid trying to output stuff.

If we don't do this, then pry can randomly exit because of a
serialization error (most usually undefined method #inspect).

lib/pry/pry_instance.rb

@@ -223,6 +223,19 @@ class Pry
     else
       print.call output, result
     end
+  rescue Exception => e
+    # Being uber-paranoid here, given that this exception arose because we couldn't
+    # serialize something in the user's program, let's not assume we can serialize
+    # the exception either.
+    begin
+      output.puts "output error: #{e.inspect}"
+    rescue Exception => e
+      if last_result_is_exception?
+        output.puts "output error: failed to show exception"
+      else
+        output.puts "output error: failed to show result"
+      end
+    end
   end
 
   # Returns true if input is "" and a command is not returning a

test/test_pry_output.rb

@@ -0,0 +1,30 @@
+
+describe Pry do
+  describe "output failsafe" do
+    after do
+      Pry.config.print = Pry::DEFAULT_PRINT
+    end
+
+    it "should catch serialization exceptions" do
+      Pry.config.print = lambda { |*a| raise "catch-22" }
+
+      lambda {
+        mock_pry("1")
+      }.should.not.raise
+    end
+
+    it "should display serialization exceptions" do
+      Pry.config.print = lambda { |*a| raise "catch-22" }
+
+      mock_pry("1").should =~ /output error: #<RuntimeError: catch-22>/
+    end
+
+    it "should catch errors serializing exceptions" do
+      Pry.config.print = lambda do |*a|
+        raise Exception.new("catch-22").tap{ |e| class << e; def inspect; raise e; end; end }
+      end
+
+      mock_pry("1").should =~ /output error: failed to show result/
+    end
+  end
+end