Prevent infinite recursion via Exception#cause

It is possible the causes of two exceptions to refer to each other.
When displaying the causes to the user rake would raise a
SystemStackError trying to show the causes repeatedly.

Now rake looks for seen causes and stops when it sees the same cause a
second time.

Fixes #272

History.rdoc

@@ -1,3 +1,10 @@
+=== 10.3.2
+
+Bug fixes:
+
+* Rake no longer infinitely loops when showing exception causes that refer to
+  each other.  Bug #272 by Chris Bandy.
+
 === 10.3.1 / 2014-04-17
 
 Bug fixes:

lib/rake/application.rb

@@ -202,6 +202,10 @@ def display_error_message(ex) # :nodoc:
     end
 
     def display_exception_details(ex) # :nodoc:
+      seen = Thread.current[:rake_display_exception_details_seen] ||= []
+      return if seen.include? ex
+      seen << ex
+
       display_exception_message_details(ex)
       display_exception_backtrace(ex)
       display_exception_details(ex.cause) if has_cause?(ex)

test/test_rake_application.rb

@@ -55,6 +55,33 @@ def test_display_exception_details_cause
     assert_match 'cause b', err
   end
 
+  def test_display_exception_details_cause_loop
+    skip 'Exception#cause not implemented' unless
+      Exception.method_defined? :cause
+
+    begin
+      begin
+        raise 'cause a'
+      rescue => a
+        begin
+          raise 'cause b'
+        rescue
+          raise a
+        end
+      end
+    rescue => ex
+    end
+
+    out, err = capture_io do
+      @app.display_error_message ex
+    end
+
+    assert_empty out
+
+    assert_match 'cause a', err
+    assert_match 'cause b', err
+  end
+
   def test_display_tasks
     @app.options.show_tasks = :tasks
     @app.options.show_task_pattern = //