Raise all I18n in development and test by default.

* Update documentation to reflect changes.
* Add TextHelpers::RaiseExceptionHandler for use with
  I18n.exception_handler.
* Add new initializer and `config.text_helpers` config bucket.

README.md

@@ -90,3 +90,40 @@ specs by adding `view: true` to the spec metadata.
 
 The controller text helpers described above can be accessed in controller
 specs by adding `controller: true` to your spec metadata.
+
+## Configuration & Initialization
+
+### Initialization
+
+`TextHelpers` performs some setup during your application's initialization. Four
+initializers are installed:
+
+#### `text_helpers.action_view.extend_base`
+
+This initializer includes the `TextHelpers::Translation` module into
+`ActionView::Base` and adds an appropriate `#translation_scope` method.
+
+#### `text_helpers.action_mailer.extend_base`
+
+This initializer includes the `TextHelpers::Translation` module into
+`ActionMailer::Base` and adds an appropriate `#translation_scope` method.
+
+#### `text_helpers.action_controller.extend_base`
+
+This initializer includes the `TextHelpers::Translation` module into
+`ActionController::Base` and adds an appropriate `#translation_scope` method.
+
+#### `text_helpers.setup_exception_handling`
+
+This initializer configures exception handling so that exceptions are raised
+if `config.text_helpers.raise_on_missing_translations` is set to `true`, which
+it is by default in the `test` or `development` environments.
+
+### Configuration
+
+#### `config.text_helpers.raise_on_missing_translations`
+
+This configuration value defaults to `true` in `test` or `development`
+environments. If set to `false`, your own exception handling can be configured
+by setting `config.action_view.raise_on_missing_translations` and
+`I18n.exception_handler` as appropriate.

lib/text_helpers.rb

@@ -2,4 +2,29 @@
 require "text_helpers/translation"
 require "text_helpers/railtie" if defined?(Rails)
 
-module TextHelpers; end
+module TextHelpers
+  # RaiseExceptionHandler just raises all exceptions, rather than swallowing
+  # MissingTranslation ones. It's cribbed almost verbatim from
+  # http://edgeguides.rubyonrails.org/i18n.html#customize-your-i18n-setup.
+  class RaiseExceptionHandler < I18n::ExceptionHandler
+    def call(exception, locale, key, options)
+      if exception.is_a?(I18n::MissingTranslation)
+        raise exception.to_exception
+      else
+        super
+      end
+    end
+  end
+
+  # Public: Install an instance of TextHelpers::RaiseExceptionHandler as the
+  # default I18n exception handler.
+  #
+  # Returns the handler instance.
+  def self.install_i18n_exception_handler
+    if I18n.exception_handler
+      Rails.logger.warn("Overwriting existing I18n exception handler")
+    end
+
+    I18n.exception_handler = RaiseExceptionHandler.new
+  end
+end

lib/text_helpers/railtie.rb

@@ -1,5 +1,8 @@
 module TextHelpers
   class Railtie < Rails::Railtie
+    config.text_helpers = ActiveSupport::OrderedOptions.new
+    config.text_helpers.raise_on_missing_translations = Rails.env.test? || Rails.env.development?
+
     initializer "text_helpers.action_view.extend_base" do
       ActionView::Base.class_eval do
         include TextHelpers::Translation
@@ -53,5 +56,15 @@ def translation_scope
         end
       end
     end
+
+    initializer "text_helpers.setup_exception_handling", after: 'after_initialize' do
+      next unless config.text_helpers.raise_on_missing_translations
+
+      if config.respond_to?(:action_view)
+        config.action_view.raise_on_missing_translations = true
+      end
+
+      TextHelpers.install_i18n_exception_handler
+    end
   end
 end