Fix double encoding specific characters with the external links

decidim-core/app/controllers/decidim/links_controller.rb

@@ -41,7 +41,7 @@ def external_url
     end
 
     def escape_url(external_url)
-      before_fragment, fragment = external_url.split("#", 2)
+      before_fragment, fragment = URI.decode_www_form_component(external_url).split("#", 2)
       escaped_before_fragment = URI::Parser.new.escape(before_fragment)
 
       if fragment

decidim-core/spec/system/external_domain_warning_spec.rb

@@ -51,6 +51,17 @@
     end
   end
 
+  context "when the source url has encoded characters" do
+    let(:destination) { "https://example.org/Me%2Cmyself%2Cand%2CI" }
+    let(:url) { "http://#{organization.host}/link?external_url=#{destination}" }
+
+    it "does not show invalid url alert" do
+      visit url
+      expect(page).to have_no_content("Invalid URL")
+      expect(page).to have_content("Me,myself,and,I")
+    end
+  end
+
   context "when url is invalid" do
     let(:invalid_url) { "http://#{organization.host}/link?external_url=foo" }