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.

features/task.feature

@@ -10,3 +10,17 @@ Feature: tasks
     When I execute the recipe
     Then the exit status must be 0
     And the output must contain "hello from recipe"
+
+  Scenario: reports errors for invalid action calls in a task
+    Given a recipe with:
+      """
+      task 'some_task' do
+        invalid_action
+      end
+      """
+    When I execute the recipe
+    Then the exit status must be 70
+    And the output must match:
+      """
+      \Arecipe.rb:2:.+invalid task action `invalid_action'
+      """

lib/producer/core.rb

@@ -1,5 +1,6 @@
 require 'producer/core/cli'
 require 'producer/core/env'
+require 'producer/core/errors'
 require 'producer/core/recipe'
 require 'producer/core/recipe/dsl'
 require 'producer/core/task'

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

spec/producer/core/cli_spec.rb

@@ -89,11 +89,13 @@ module Producer::Core
             }
         end
 
-        it 'prints the error' do
-          begin
-            cli.evaluate_recipe_file
-          rescue SystemExit
-          end
+        def trap_exit
+          yield
+        rescue SystemExit
+        end
+
+        it 'prints the specific error' do
+          trap_exit { cli.evaluate_recipe_file }
           expect(stdout.string).to match(/
             \A
             #{recipe_file}:4:
@@ -101,6 +103,11 @@ module Producer::Core
             invalid\srecipe\skeyword\s`invalid_keyword'
           /x)
         end
+
+        it 'excludes producer own source code from the error backtrace' do
+          trap_exit { cli.evaluate_recipe_file }
+          expect(stdout.string).to_not match /\/producer-core\//
+        end
       end
     end
   end

spec/producer/core/recipe/dsl_spec.rb

@@ -50,7 +50,7 @@ module Producer::Core
 
         it 'raises a RecipeEvaluationError on NameError' do
           dsl = Recipe::DSL.new { invalid_keyword }
-          expect { dsl.evaluate(env) }.to raise_error(Recipe::RecipeEvaluationError)
+          expect { dsl.evaluate(env) }.to raise_error(RecipeEvaluationError)
         end
       end
     end

spec/producer/core/task/dsl_spec.rb

@@ -12,6 +12,14 @@ module Producer::Core
         expect { dsl.evaluate(env) }
           .to raise_error(RuntimeError, 'error from task')
       end
+
+      context 'when given block is invalid' do
+        it 'raises a TaskEvaluationError on NameError' do
+          dsl = Task::DSL.new { invalid_action }
+          expect { dsl.evaluate(env) }
+            .to raise_error(TaskEvaluationError)
+        end
+      end
     end
 
     describe '#condition' do