more explicit error for failed actions

lib/bond/agent.rb

@@ -16,6 +16,8 @@ def complete(options={}, &block)
 
     def call(input)
       (mission = find_mission(input)) ? mission.execute : default_mission.execute(input)
+    rescue FailedExecutionError
+      $stderr.puts "", $!.message
     rescue
       p $!
       p $!.backtrace.slice(0,5)

lib/bond/mission.rb

@@ -1,5 +1,6 @@
 module Bond
   class InvalidMissionError < StandardError; end
+  class FailedExecutionError < StandardError; end
   class Mission
     attr_reader :action, :default
 
@@ -49,11 +50,15 @@ def matches?(input)
     def execute(*args)
       if args.empty?
         list = @action.call(@input)
-        list = @search ? @search.call(@input, list) : list
+        list = (@search ? @search.call(@input, list) : list) || []
         @list_prefix ? list.map {|e| @list_prefix + e } : list
       else
         @action.call(*args)
       end
+    rescue
+      error_message = "Mission action failed to execute properly. Check your mission action for pattern #{@condition.inspect}.\n" +
+        "Failed with error: #{$!.message}"
+      raise FailedExecutionError, error_message
     end
 
     def default_search(input, list)

test/agent_test.rb

@@ -32,12 +32,17 @@ class Bond::AgentTest < Test::Unit::TestCase
       complete 'blah'
     end
 
-    test "chooses default mission if mission processing fails" do
+    test "chooses default mission if internal processing fails" do
       Bond.complete(:on=>/bling/) {|e| [] }
       Bond.agent.expects(:find_mission).raises
       Bond.agent.default_mission.expects(:execute)
       complete('bling')
     end
+
+    test "prints error if action generates failure" do
+      Bond.complete(:on=>/bling/) {|e| raise "whoops" }
+      capture_stderr { complete('bling') }.should =~ /bling.*whoops/m
+    end
   end
 
   test "default_mission set to a valid mission if irb doesn't exist" do

test/mission_test.rb

@@ -17,7 +17,7 @@ class Bond::MissionTest < Test::Unit::TestCase
       complete('cool c', 'c').should == %w{cd}
     end
 
-    test "with quoted method completes" do
+    test "with method and quoted argument completes" do
       Bond.complete(:on=>/bling/) {|e| [] }
       Bond.complete(:method=>'cool') {|e| %w{ab cd ef ad} }
       complete('cool "a', 'a').should == %w{ab ad}