Improve error reporting during recipe evaluation

* Report invalid action usages from tasks;
* Implement backtrace cleaning in CLI;
* Extract error class declarations in a new errors file;
* Replace raise with fail keyword in task DSL class.

lib/producer/core/cli.rb

@@ -24,9 +24,10 @@ module Producer
         env = Env.new(recipe)
         begin
           recipe.evaluate env
-        rescue Recipe::RecipeEvaluationError => e
-          @stdout.puts [e.backtrace.shift, e.message].join ': '
-          @stdout.puts e.backtrace
+        rescue RecipeEvaluationError => e
+          backtrace = e.backtrace.reject { |l| l =~ /\/producer-core\// }
+          @stdout.puts [backtrace.shift, e.message].join ': '
+          @stdout.puts backtrace
 
           exit 70
         end

lib/producer/core/errors.rb

@@ -0,0 +1,8 @@
+module Producer
+  module Core
+    Error                 = Class.new(StandardError)
+    ConditionNotMetError  = Class.new(Error)
+    RecipeEvaluationError = Class.new(StandardError)
+    TaskEvaluationError   = Class.new(RecipeEvaluationError)
+  end
+end

lib/producer/core/recipe.rb

@@ -1,8 +1,6 @@
 module Producer
   module Core
     class Recipe
-      RecipeEvaluationError = Class.new(StandardError)
-
       attr_reader :code, :filepath
 
       def self.from_file(filepath)

lib/producer/core/recipe/dsl.rb

@@ -18,9 +18,9 @@ module Producer
           end
           self
         rescue NameError => e
-          err = RecipeEvaluationError.new("invalid recipe keyword `#{e.name}'")
-          err.set_backtrace e.backtrace.reject { |l| l =~ /\/producer-core\// }
-          raise err
+          raise RecipeEvaluationError,
+            "invalid recipe keyword `#{e.name}'",
+            e.backtrace
         end
 
         private

lib/producer/core/task/dsl.rb

@@ -2,8 +2,6 @@ module Producer
   module Core
     class Task
       class DSL
-        ConditionNotMetError = Class.new(StandardError)
-
         def initialize(&block)
           @block = block
         end
@@ -11,10 +9,14 @@ module Producer
         def evaluate(env)
           instance_eval &@block
         rescue ConditionNotMetError
+        rescue NameError => e
+          raise TaskEvaluationError,
+            "invalid task action `#{e.name}'",
+            e.backtrace
         end
 
         def condition(&block)
-          raise ConditionNotMetError unless block.call
+          fail ConditionNotMetError unless block.call
         end
       end
     end