FIX: Category redirect to correct slug should not loop (#11772)

The server responds with a redirect to URLs with wrong slugs, even when
the slug was the correct but in the encoded form (if it contained
special characters).

app/controllers/list_controller.rb

@@ -360,7 +360,7 @@ class ListController < ApplicationController
       current_slug = current_slug.split("/").map { |slug| CGI.escape(slug) }.join("/")
     end
     real_slug = @category.full_slug("/")
-    if current_slug != real_slug
+    if CGI.unescape(current_slug) != CGI.unescape(real_slug)
       url = request.fullpath.gsub(current_slug, real_slug)
       if ActionController::Base.config.relative_url_root
         url = url.sub(ActionController::Base.config.relative_url_root, "")

spec/requests/list_controller_spec.rb

@@ -759,6 +759,37 @@ RSpec.describe ListController do
       get "/c/hello/world/bye/#{subsubcategory.id}"
       expect(response.status).to eq(301)
       expect(response).to redirect_to("/c/#{category.slug}/#{subcategory.slug}/#{subsubcategory.slug}/#{subsubcategory.id}")
+
+      get "/c/#{category.slug}/#{subcategory.slug}/#{subsubcategory.slug}/#{subsubcategory.id}"
+      expect(response.status).to eq(200)
+    end
+
+    it "redirects to URL with correct case slug" do
+      category.update!(slug: "hello")
+
+      get "/c/Hello/#{category.id}"
+      expect(response).to redirect_to("/c/hello/#{category.id}")
+
+      get "/c/hello/#{category.id}"
+      expect(response.status).to eq(200)
+    end
+
+    context "does not create a redirect loop" do
+      it "with encoded slugs" do
+        category = Fabricate(:category)
+        category.update_columns(slug: CGI.escape("systèmes"))
+
+        get "/c/syst%C3%A8mes/#{category.id}"
+        expect(response.status).to eq(200)
+      end
+
+      it "with lowercase encoded slugs" do
+        category = Fabricate(:category)
+        category.update_columns(slug: CGI.escape("systèmes").downcase)
+
+        get "/c/syst%C3%A8mes/#{category.id}"
+        expect(response.status).to eq(200)
+      end
     end
 
     context "with subfolder" do