When truncating an object using ObjectFormatter.format that exceeds the max_formatted_output_length remove any partial ANSI color codes.

This fixes an edge case where partial ANSI color codes eg \e[3 is printed to the terminal which corrupts the output.

eg calling object.inspect = "#<\e[33mClass\e[0m \e[36mname: \e[0m\"foobars\" \e[36mcount: \e[0m42>"
If this was truncated at the 19th char then the result would be: "#<\e[33mClass\e[0m \e[3"
This commit will remove the partial ANSI code so the result is now: "#<\e[33mClass\e[0m "

This fixes an edge case where

Author: ansonK

lib/rspec/support/object_formatter.rb

@@ -37,8 +37,8 @@ def format(object)
           if formatted_object.length < max_formatted_output_length
             return formatted_object
           else
-            beginning = formatted_object[0 .. max_formatted_output_length / 2]
-            ending = formatted_object[-max_formatted_output_length / 2 ..-1]
+            beginning = truncate_string formatted_object, 0, max_formatted_output_length / 2
+            ending = truncate_string formatted_object, -max_formatted_output_length / 2, -1
             return beginning + ELLIPSIS + ending
           end
         end
@@ -244,6 +244,20 @@ def inspect
         DelegatorInspector,
         InspectableObjectInspector
       ]
+
+    private
+
+      # Returns the substring defined by the start_index and end_index
+      # If the string ends with a partial ANSI code code then that
+      # will be removed as printing partial ANSI
+      # codes to the terminal can lead to corruption
+      def truncate_string(str, start_index, end_index)
+        cut_str = str[start_index..end_index]
+
+        # ANSI color codes are like: \e[33m so anything with \e[ and a
+        # number without a 'm' is an incomplete color code
+        cut_str.sub(/\e\[\d+$/, '')
+      end
     end
   end
 end

spec/rspec/support/object_formatter_spec.rb

@@ -310,6 +310,18 @@ def self.to_s
           formatter = ObjectFormatter.new(10)
           expect(formatter.format('Testing')).to eq('"Testing"')
         end
+
+        context 'with ANSI escape codes that fall on the truncate split' do
+          it 'removes that escape code so terminals do not get corrupted print a partial escape code' do
+            formatter = ObjectFormatter.new(38)
+            object = Class.new do
+              def inspect
+                "#<\e[33mClass\e[0m \e[36mname: \e[0m\"foobars\" \e[36mcount: \e[0m42>"
+              end
+            end.new
+            expect(formatter.format(object)).to eq("#<\e[33mClass\e[0m ...\e[36mcount: \e[0m42>")
+          end
+        end
       end
 
       context 'with truncation disabled' do