Add I18n interface for mustache templates

This commit adds an interface that allows mustache templates to get I18n
translation strings, transform any arguments that may be present in
them, and then render them on the frontend.

This is our first real step to getting internationalizing the Gollum
frontend.

test/gollum/views/test_locale_helper.rb

@@ -0,0 +1,134 @@
+require_relative "../../helper"
+require_relative "../../../lib/gollum/views/helpers"
+
+describe Precious::Views::LocaleHelpers do
+  class TestClass < Mustache
+    include Precious::Views::LocaleHelpers
+
+    def author
+      "J.R.R."
+    end
+
+    def location
+      "Bloemfontein"
+    end
+  end
+
+  def setup
+    ::I18n.available_locales = [:en, :de]
+    ::I18n.load_path = Dir[File.expand_path("test/support/locales" + "/*.yml")]
+  end
+
+  def teardown
+    I18n.locale = :en
+  end
+
+  let(:dummy_instance) { TestClass.new }
+
+  describe "#t" do
+    describe "mustache usage" do
+      let(:subject) { dummy_instance.render(mustache_template) }
+
+      let(:mustache_template) { "{{ t.hello_world }}" }
+
+      describe "in the default locale" do
+        it "returns the translation string" do
+          _(subject).must_equal "Hello world"
+        end
+      end
+
+      describe "in the configured locale" do
+        it "returns the translation string" do
+          I18n.locale = :de
+
+          _(subject).must_equal "Hallo Welt"
+        end
+      end
+
+      describe "translations with YAML arguments" do
+        let(:mustache_template) { "{{ t.author_info.full }}" }
+
+        describe "in the default locale" do
+          it "autofills YAML arguments" do
+            _(subject).must_equal "Author J.R.R. is from Bloemfontein"
+          end
+        end
+
+        describe "in the configured locale" do
+          it "autofills YAML arguments" do
+            I18n.locale = :de
+
+            _(subject).must_equal "Autor J.R.R. ist vom Bloemfontein"
+          end
+        end
+      end
+
+      describe "translations with invalid arguments" do
+        let(:mustache_template) { "{{ t.has_invalid_argument }}" }
+
+        it "fails gracefully with embedded error message" do
+          expected_string = "Welcome to " \
+            "[#{TestClass::NO_METHOD_MESSAGE}: no_matching_method]"
+
+          _(subject).must_equal expected_string
+        end
+      end
+
+      describe "out of scope translations" do
+        let(:mustache_template) { "{{ t.never_called }}" }
+
+        it "does not include translation keys from other classes" do
+          _(subject).must_be_empty
+        end
+      end
+
+      describe "missing translations" do
+        let(:mustache_template) { "{{ t.nested.nonexistent_key }}" }
+
+        it "outputs an empty string" do
+          _(subject).must_be_empty
+        end
+      end
+    end
+
+    describe "usage" do
+      let(:subject) { dummy_instance.t }
+
+      it "returns a hash" do
+        _(subject).must_be_kind_of Hash
+      end
+
+      it "returns translation keys under 'test_class'" do
+        i18n_keys = I18n.t("test_class").keys
+
+        _(subject.keys).must_equal i18n_keys
+      end
+
+      it "does not return translation keys under other classes" do
+        other_i18n_keys = I18n.t("nonexistant_test_class").keys
+
+        _(subject.keys).wont_include other_i18n_keys
+      end
+
+      it "returns nested keys" do
+        nested_keys = subject[:author_info].keys
+
+        _(nested_keys).must_equal [:full]
+      end
+
+      describe "auto-filled YAML arguments" do
+        let(:subject) { dummy_instance.t[:author_info][:full] }
+
+        it "auto-fills in the default locale" do
+          _(subject).must_equal "Author J.R.R. is from Bloemfontein"
+        end
+
+        it "auto-fills in a configured locale" do
+          I18n.locale = :de
+
+          _(subject).must_equal "Autor J.R.R. ist vom Bloemfontein"
+        end
+      end
+    end
+  end
+end

test/helper.rb

@@ -5,6 +5,7 @@ require 'shoulda'
 require 'mocha/setup'
 require 'fileutils'
 require 'minitest/reporters'
+require 'minitest/spec'
 require 'twitter_cldr'
 require 'tmpdir'
 
@@ -93,4 +94,4 @@ def context(*args, &block)
   klass.class_eval &block
 end
 
-$contexts = []
+$contexts = []

test/support/locales/de.yml

@@ -0,0 +1,8 @@
+de:
+  test_class:
+    author_info:
+      full: Autor %{author} ist vom %{location}
+    has_invalid_argument: Willkommen in %{no_matching_method}
+    hello_world: Hallo Welt
+  nonexistant_test_class:
+    never_called: Nie angerufen

test/support/locales/en.yml

@@ -0,0 +1,8 @@
+en:
+  test_class:
+    author_info:
+      full: Author %{author} is from %{location}
+    has_invalid_argument: Welcome to %{no_matching_method}
+    hello_world: Hello world
+  nonexistant_test_class:
+    never_called: Never called