FEATURE: Mixed case tagging (#6454)

- By default, behaviour is not changed: tags are made lowercase upon creation and edit.

- If force_lowercase_tags is disabled, then mixed case tags are allowed.

- Tags must remain case-insensitively unique. This is enforced by ActiveRecord and Postgres.

- A migration is added to provide a `UNIQUE` index on `lower(name)`. Migration includes a safety to correct any current tags that do not meet the criteria.

- A `where_name` scope is added to `models/tag.rb`, to allow easy case-insensitive lookups. This is used instead of `Tag.where(name: "blah")`.

- URLs remain lowercase. Mixed case URLs are functional, but have the lowercase equivalent as the canonical.

spec/components/discourse_tagging_spec.rb

@@ -13,7 +13,7 @@ describe DiscourseTagging do
 
   let!(:tag1) { Fabricate(:tag, name: "fun") }
   let!(:tag2) { Fabricate(:tag, name: "fun2") }
-  let!(:tag3) { Fabricate(:tag, name: "fun3") }
+  let!(:tag3) { Fabricate(:tag, name: "Fun3") }
 
   before do
     SiteSetting.tagging_enabled = true
@@ -186,7 +186,8 @@ describe DiscourseTagging do
 
       it "returns only existing tag names" do
         Fabricate(:tag, name: 'oldtag')
-        expect(described_class.tags_for_saving(['newtag', 'oldtag'], guardian).try(:sort)).to eq(['oldtag'])
+        Fabricate(:tag, name: 'oldTag2')
+        expect(described_class.tags_for_saving(['newtag', 'oldtag', 'oldtag2'], guardian)).to contain_exactly('oldtag', 'oldTag2')
       end
     end
 
@@ -205,5 +206,13 @@ describe DiscourseTagging do
         expect(described_class.tags_for_saving(['math=fun', 'fun*2@gmail.com'], guardian).try(:sort)).to eq(['math=fun', 'fun2gmailcom'].sort)
       end
     end
+
+    describe "clean_tag" do
+      it "downcases new tags if setting enabled" do
+        expect(DiscourseTagging.clean_tag("HeLlO")).to eq("hello")
+        SiteSetting.force_lowercase_tags = false
+        expect(DiscourseTagging.clean_tag("HeLlO")).to eq("HeLlO")
+      end
+    end
   end
 end

spec/components/search_spec.rb

@@ -407,6 +407,7 @@ describe Search do
     end
 
     let!(:tag) { Fabricate(:tag) }
+    let!(:uppercase_tag) { Fabricate(:tag, name: "HeLlO") }
     let(:tag_group) { Fabricate(:tag_group) }
     let(:category) { Fabricate(:category) }
 
@@ -415,7 +416,7 @@ describe Search do
         SiteSetting.tagging_enabled = true
 
         post = Fabricate(:post, raw: 'I am special post')
-        DiscourseTagging.tag_topic_by_names(post.topic, Guardian.new(Fabricate.build(:admin)), [tag.name])
+        DiscourseTagging.tag_topic_by_names(post.topic, Guardian.new(Fabricate.build(:admin)), [tag.name, uppercase_tag.name])
         post.topic.save
 
         # we got to make this index (it is deferred)
@@ -424,6 +425,9 @@ describe Search do
         result = Search.execute(tag.name)
         expect(result.posts.length).to eq(1)
 
+        result = Search.execute("hElLo")
+        expect(result.posts.length).to eq(1)
+
         SiteSetting.tagging_enabled = false
 
         result = Search.execute(tag.name)
@@ -822,9 +826,10 @@ describe Search do
       expect(Search.execute("sams post #sub-category").posts.length).to eq(1)
 
       # tags
-      topic.tags = [Fabricate(:tag, name: 'alpha'), Fabricate(:tag, name: 'привет')]
+      topic.tags = [Fabricate(:tag, name: 'alpha'), Fabricate(:tag, name: 'привет'), Fabricate(:tag, name: 'HeLlO')]
       expect(Search.execute('this is a test #alpha').posts.map(&:id)).to eq([post.id])
       expect(Search.execute('this is a test #привет').posts.map(&:id)).to eq([post.id])
+      expect(Search.execute('this is a test #hElLo').posts.map(&:id)).to eq([post.id])
       expect(Search.execute('this is a test #beta').posts.size).to eq(0)
     end
 

spec/components/topic_query_spec.rb

@@ -160,6 +160,7 @@ describe TopicQuery do
   context 'tag filter' do
     let(:tag)       { Fabricate(:tag) }
     let(:other_tag) { Fabricate(:tag) }
+    let(:uppercase_tag) { Fabricate(:tag, name: "HeLlO") }
 
     before do
       SiteSetting.tagging_enabled = true
@@ -169,6 +170,7 @@ describe TopicQuery do
       let!(:tagged_topic1) { Fabricate(:topic, tags: [tag]) }
       let!(:tagged_topic2) { Fabricate(:topic, tags: [other_tag]) }
       let!(:tagged_topic3) { Fabricate(:topic, tags: [tag, other_tag]) }
+      let!(:tagged_topic4) { Fabricate(:topic, tags: [uppercase_tag]) }
       let!(:no_tags_topic) { Fabricate(:topic) }
 
       it "returns topics with the tag when filtered to it" do
@@ -186,6 +188,9 @@ describe TopicQuery do
 
         expect(TopicQuery.new(moderator, tags: [tag.id, other_tag.id]).list_latest.topics)
           .to contain_exactly(tagged_topic1, tagged_topic2, tagged_topic3)
+
+        expect(TopicQuery.new(moderator, tags: ["hElLo"]).list_latest.topics)
+          .to contain_exactly(tagged_topic4)
       end
 
       it "can return topics with all specified tags" do