Backport Fix '/unassign' slash command

app/services/slash_commands/interpret_service.rb

@@ -92,26 +92,20 @@ module SlashCommands
     desc 'Assign'
     explanation do |users|
-      "Assigns #{users.map(&:to_reference).to_sentence}." if users.any?
+      "Assigns #{users.first.to_reference}." if users.any?
     end
     params '@user'
     condition do
       current_user.can?(:"admin_#{issuable.to_ability_name}", project)
     end
     parse_params do |assignee_param|
-      users = extract_references(assignee_param, :user)
-
-      if users.empty?
-        users = User.where(username: assignee_param.split(' ').map(&:strip))
-      end
-
-      users
+      extract_users(assignee_param)
     end
     command :assign do |users|
       next if users.empty?
       if issuable.is_a?(Issue)
-        @updates[:assignee_ids] = users.map(&:id)
+        @updates[:assignee_ids] = [users.last.id]
       else
         @updates[:assignee_id] = users.last.id
       end
@@ -459,6 +453,18 @@ module SlashCommands
       end
     end
+    def extract_users(params)
+      return [] if params.nil?
+
+      users = extract_references(params, :user)
+
+      if users.empty?
+        users = User.where(username: params.split(' ').map(&:strip))
+      end
+
+      users
+    end
+
     def find_labels(labels_param)
       extract_references(labels_param, :label) |
         LabelsFinder.new(current_user, project_id: project.id, name: labels_param.split).execute

lib/gitlab/slash_commands/command_definition.rb

@@ -48,17 +48,23 @@ module Gitlab
       end
       def to_h(opts)
+        context = OpenStruct.new(opts)
+
         desc = description
         if desc.respond_to?(:call)
-          context = OpenStruct.new(opts)
           desc = context.instance_exec(&desc) rescue ''
         end
+        prms = params
+        if prms.respond_to?(:call)
+          prms = Array(context.instance_exec(&prms)) rescue params
+        end
+
         {
           name: name,
           aliases: aliases,
           description: desc,
-          params: params
+          params: prms
         }
       end

lib/gitlab/slash_commands/dsl.rb

@@ -40,8 +40,8 @@ module Gitlab
         #   command :command_key do |arguments|
         #     # Awesome code block
         #   end
-        def params(*params)
-          @params = params
+        def params(*params, &block)
+          @params = block_given? ? block : params
         end
         # Allows to give an explanation of what the command will do when

spec/services/issuable/bulk_update_service_spec.rb

@@ -72,7 +72,7 @@ describe Issuable::BulkUpdateService, services: true do
     end
     context "when the new assignee ID is #{IssuableFinder::NONE}" do
-      it "unassigns the issues" do
+      it 'unassigns the issues' do
         expect { bulk_update(merge_request, assignee_id: IssuableFinder::NONE) }
           .to change { merge_request.reload.assignee }.to(nil)
       end

spec/services/slash_commands/interpret_service_spec.rb

@@ -384,7 +384,7 @@ describe SlashCommands::InterpretService, services: true do
         it 'fetches assignee and populates assignee_id if content contains /assign' do
           _, updates = service.execute(content, issue)
-          expect(updates[:assignee_ids]).to match_array([developer.id, developer2.id])
+          expect(updates[:assignee_ids]).to match_array([developer.id])
         end
       end