FIX: Topic#title were being parameterized when encoded slug is

enabled.

lib/slug.rb

@@ -25,11 +25,12 @@ module Slug
 
   private
 
-  def self.prettify_slug(slug, max_length: MAX_LENGTH)
+  def self.prettify_slug(slug, max_length:)
-    slug.tr!("_", "-")
+    slug
-    slug = slug.squeeze('-') # squeeze continuous dashes to prettify slug
+      .tr("_", "-")
-    slug.gsub!(/\A-+|-+\z/, '') # remove possible trailing and preceding dashes
+      .truncate(max_length, omission: '')
-    slug.truncate(max_length, omission: '')
+      .squeeze('-') # squeeze continuous dashes to prettify slug
+      .gsub(/\A-+|-+\z/, '') # remove possible trailing and preceding dashes
   end
 
   def self.ascii_generator(string)
@@ -40,11 +41,11 @@ module Slug
     # This generator will sanitize almost all special characters,
     # including reserved characters from RFC3986.
     # See also URI::REGEXP::PATTERN.
-    string.strip!
+    string = string.strip
-    string.gsub!(/\s+/, '-')
+      .gsub(/\s+/, '-')
-    string.gsub!(CHAR_FILTER_REGEXP, '')
+      .gsub(CHAR_FILTER_REGEXP, '')
-    string.downcase! if downcase
+
-    string
+    downcase ? string.downcase : string
   end
 
   def self.none_generator(string)

spec/models/topic_spec.rb

@@ -123,21 +123,25 @@ describe Topic do
   context 'slug' do
     let(:title) { "hello world topic" }
     let(:slug) { "hello-world-topic" }
+    let!(:expected_title) { title.dup }
+    let!(:expected_slug) { slug.dup }
+    let(:topic) { Fabricate.build(:topic, title: title) }
+
     context 'encoded generator' do
       before { SiteSetting.slug_generation_method = 'encoded' }
-      after { SiteSetting.slug_generation_method = 'ascii' }
 
       it "returns a Slug for a title" do
-        Slug.expects(:for).with(title).returns(slug)
+        expect(topic.title).to eq(expected_title)
-        expect(Fabricate.build(:topic, title: title).slug).to eq(slug)
+        expect(topic.slug).to eq(expected_slug)
       end
 
       context 'for cjk characters' do
         let(:title) { "熱帶風暴畫眉" }
-        let(:slug) { "熱帶風暴畫眉" }
+        let!(:expected_title) { title.dup }
+
         it "returns encoded Slug for a title" do
-          Slug.expects(:for).with(title).returns(slug)
+          expect(topic.title).to eq(expected_title)
-          expect(Fabricate.build(:topic, title: title).slug).to eq(slug)
+          expect(topic.slug).to eq(expected_title)
         end
       end
 
@@ -153,7 +157,7 @@ describe Topic do
 
     context 'none generator' do
       before { SiteSetting.slug_generation_method = 'none' }
-      after { SiteSetting.slug_generation_method = 'ascii' }
+
       let(:title) { "熱帶風暴畫眉" }
       let(:slug) { "topic" }
 
@@ -165,6 +169,7 @@ describe Topic do
 
     context '#ascii_generator' do
       before { SiteSetting.slug_generation_method = 'ascii' }
+
       it "returns a Slug for a title" do
         Slug.expects(:for).with(title).returns(slug)
         expect(Fabricate.build(:topic, title: title).slug).to eq(slug)
@@ -173,6 +178,7 @@ describe Topic do
       context 'for cjk characters' do
         let(:title) { "熱帶風暴畫眉" }
         let(:slug) { 'topic' }
+
         it "returns 'topic' when the slug is empty (say, non-latin characters)" do
           Slug.expects(:for).with(title).returns("topic")
           expect(Fabricate.build(:topic, title: title).slug).to eq("topic")