Display snippet for missing parameter types

CHANGELOG.md

@@ -26,7 +26,7 @@ Please visit [cucumber/CONTRIBUTING.md](https://github.com/cucumber/cucumber/blo
 
 ### Improved
 
-* N/A
+* Display snippet when using undefined parameter type [#1411](https://github.com/cucumber/cucumber-ruby/issues/1411)
 
 ## [4.0.0.rc.6](https://github.com/cucumber/cucumber-ruby/compare/v4.0.0.rc.5...4.0.0.rc.6)
 

features/docs/defining_steps/snippets.feature

@@ -81,3 +81,31 @@ Feature: Snippets
         pending # Write code here that turns the phrase above into concrete actions
       end
       """
+
+  Scenario: Snippet for step definition with undefined parameter type
+    Given a file named "features/undefined_parameter_type.feature" with:
+      """
+      Feature:
+        Scenario: Delayed flight
+          Given leg LHR-OSL is cancelled
+      """
+    And a file named "features/steps.rb" with:
+      """
+      Given('leg {flight-leg} is cancelled') do |flight|
+        log flight.to_s
+      end
+      """
+    When I run `cucumber features/undefined_parameter_type.feature -s`
+    Then the output should contain:
+      """
+      The parameter flight-leg is not defined. You can define a new one with:
+
+      ParameterType(
+        name:        'flight-leg',
+        regexp:      /some regexp here/,
+        type:        FlightLeg,
+        # The transformer takes as many arguments as there are capture groups in the regexp,
+        # or just one if there are none.
+        transformer: ->(s) { FlightLeg.new(s) }
+      )
+      """

lib/cucumber/events.rb

@@ -38,7 +38,8 @@ def self.registry
         TestStepCreated,
         TestStepFinished,
         TestStepStarted,
-        Envelope
+        Envelope,
+        UndefinedParameterType
       )
     end
   end

lib/cucumber/events/undefined_parameter_type.rb

@@ -0,0 +1,10 @@
+require 'cucumber/core/events'
+
+module Cucumber
+  module Events
+    class UndefinedParameterType < Core::Event.new(:type_name, :expression)
+      attr_reader :type_name
+      attr_reader :expression
+    end
+  end
+end

lib/cucumber/formatter/console.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+# rubocop:disable Metrics/ModuleLength
+
 require 'cucumber/formatter/ansicolor'
 require 'cucumber/formatter/duration'
 require 'cucumber/gherkin/i18n'
@@ -116,14 +118,21 @@ def collect_snippet_data(test_step, ast_lookup)
         @snippets_input << Console::SnippetData.new(keyword, test_step)
       end
 
+      def collect_undefined_parameter_type_names(undefined_parameter_type)
+        @undefined_parameter_types << undefined_parameter_type.type_name
+      end
+
       def print_snippets(options)
         return unless options[:snippets]
-        return if @snippets_input.empty?
 
         snippet_text_proc = lambda do |step_keyword, step_name, multiline_arg|
           snippet_text(step_keyword, step_name, multiline_arg)
         end
-        do_print_snippets(snippet_text_proc)
+        do_print_snippets(snippet_text_proc) unless @snippets_input.empty?
+
+        @undefined_parameter_types.map do |type_name|
+          do_print_undefined_parameter_type_snippet(type_name)
+        end
       end
 
       def do_print_snippets(snippet_text_proc)
@@ -181,6 +190,24 @@ def do_print_profile_information(profiles)
         @io.puts "Using the #{profiles_sentence} profile#{'s' if profiles.size > 1}..."
       end
 
+      def do_print_undefined_parameter_type_snippet(type_name)
+        camelized = type_name.split(/_|-/).collect(&:capitalize).join
+
+        @io.puts [
+          "The parameter #{type_name} is not defined. You can define a new one with:",
+          '',
+          'ParameterType(',
+          "  name:        '#{type_name}',",
+          '  regexp:      /some regexp here/,',
+          "  type:        #{camelized},",
+          '  # The transformer takes as many arguments as there are capture groups in the regexp,',
+          '  # or just one if there are none.',
+          "  transformer: ->(s) { #{camelized}.new(s) }",
+          ')',
+          ''
+        ].join("\n")
+      end
+
       private
 
       FORMATS = Hash.new { |hash, format| hash[format] = method(format).to_proc }
@@ -219,3 +246,4 @@ def initialize(actual_keyword, step)
     end
   end
 end
+# rubocop:enable Metrics/ModuleLength

lib/cucumber/formatter/message_builder.rb

@@ -29,6 +29,7 @@ def initialize(config)
         config.on_event :test_step_finished, &method(:on_test_step_finished)
         config.on_event :test_case_finished, &method(:on_test_case_finished)
         config.on_event :test_run_finished, &method(:on_test_run_finished)
+        config.on_event :undefined_parameter_type, &method(:on_undefined_parameter_type)
 
         @test_case_by_step_id = {}
         @current_test_case_started_id = nil
@@ -235,6 +236,17 @@ def on_test_run_finished(*)
         output_envelope(message)
       end
 
+      def on_undefined_parameter_type(event)
+        message = Cucumber::Messages::Envelope.new(
+          undefined_parameter_type: Cucumber::Messages::UndefinedParameterType.new(
+            name: event.type_name,
+            expression: event.expression
+          )
+        )
+
+        output_envelope(message)
+      end
+
       def test_case_started_id(test_case)
         @test_case_started_by_test_case.test_case_started_id_by_test_case(test_case)
       end

lib/cucumber/formatter/pretty.rb

@@ -36,6 +36,7 @@ def initialize(config)
         @config = config
         @options = config.to_hash
         @snippets_input = []
+        @undefined_parameter_types = []
         @total_duration = 0
         @exceptions = []
         @gherkin_sources = {}
@@ -54,13 +55,19 @@ def initialize(config)
         @passed_test_cases = []
         @source_indent = 0
         @next_comment_to_be_printed = 0
+
+        bind_events(config)
+      end
+
+      def bind_events(config)
         config.on_event :gherkin_source_read, &method(:on_gherkin_source_read)
         config.on_event :step_activated, &method(:on_step_activated)
         config.on_event :test_case_started, &method(:on_test_case_started)
         config.on_event :test_step_started, &method(:on_test_step_started)
         config.on_event :test_step_finished, &method(:on_test_step_finished)
         config.on_event :test_case_finished, &method(:on_test_case_finished)
         config.on_event :test_run_finished, &method(:on_test_run_finished)
+        config.on_event :undefined_parameter_type, &method(:collect_undefined_parameter_type_names)
       end
 
       def on_gherkin_source_read(event)

lib/cucumber/formatter/progress.rb

@@ -21,6 +21,7 @@ def initialize(config)
         @config = config
         @io = ensure_io(config.out_stream)
         @snippets_input = []
+        @undefined_parameter_types = []
         @total_duration = 0
         @matches = {}
         @pending_step_matches = []
@@ -36,6 +37,7 @@ def initialize(config)
         config.on_event :test_step_finished, &method(:on_test_step_finished)
         config.on_event :test_case_finished, &method(:on_test_case_finished)
         config.on_event :test_run_finished, &method(:on_test_run_finished)
+        config.on_event :undefined_parameter_type, &method(:collect_undefined_parameter_type_names)
       end
 
       def on_step_activated(event)

lib/cucumber/glue/registry_and_more.rb

@@ -93,12 +93,7 @@ def register_rb_step_definition(string_or_regexp, proc_or_sym, options)
         # TODO: add a way to extract the parameter type directly from the error.
         type_name = e.message.match(/^Undefined parameter type \{(.*)\}$/)[1]
 
-        @configuration.notify :envelope, Cucumber::Messages::Envelope.new(
-          undefined_parameter_type: Cucumber::Messages::UndefinedParameterType.new(
-            name: type_name,
-            expression: string_or_regexp
-          )
-        )
+        @configuration.notify :undefined_parameter_type, type_name, string_or_regexp
       end
 
       def build_rb_world_factory(world_modules, namespaced_world_modules, proc)