Add Inherit quick action

Closes #38450

app/services/quick_actions/interpret_service.rb

@@ -268,6 +268,24 @@ module QuickActions
       end
     end
 
+    desc 'Inherit (copy) labels and milestone from other issue'
+    explanation do |issue_id|
+      "Inherit (copy) labels and milestone from issue \"#{issue_id}\"."
+    end
+    params '#issue'
+    condition do
+      issuable.persisted? &&
+        current_user.can?(:"update_#{issuable.to_ability_name}", issuable)
+    end
+    command :inherit do |issue_id|
+      issue = extract_references(issue_id, :issue).first
+      if issue.present? && issue.project_id == issuable.project_id
+        @updates[:add_label_ids] = issue.labels.map(&:id)
+
+        @updates[:milestone_id] = issue.milestone.id if issue.milestone
+      end
+    end
+
     desc 'Add a todo'
     explanation 'Adds a todo.'
     condition do

changelogs/unreleased/add-inherit-command.yml

+---
+title: Add Inherit quick action
+merge_request:
+author: Mateusz Bajorski
+type: added

doc/user/project/quick_actions.md

@@ -40,4 +40,5 @@ do.
 | `/duplicate #issue`        | Closes this issue and marks it as a duplicate of another issue |
 | `/move path/to/project`	     | Moves issue to another project |
 | `/tableflip`	             | Append the comment with `(╯°□°)╯︵ ┻━┻` |
-| `/shrug`	                 | Append the comment with `¯\＿(ツ)＿/¯` |
\ No newline at end of file
+| `/shrug`	                 | Append the comment with `¯\＿(ツ)＿/¯` |
+| `/inherit #issue`          | Inherit (copy) labels and milestone from other issue |

spec/services/quick_actions/interpret_service_spec.rb

@@ -306,6 +306,23 @@ describe QuickActions::InterpretService do
       end
     end
 
+    shared_examples 'inherit command' do
+      it 'fetches issue and copies labels and milestone if content contains /inherit issue_reference' do
+        issue_father # populate the issue
+        todo_label # populate this label
+        inreview_label # populate this label
+        _, updates = service.execute(content, issuable)
+
+        expect(updates[:add_label_ids]).to match_array([inreview_label.id, todo_label.id])
+
+        if issue_father.milestone
+          expect(updates[:milestone_id]).to eq(issue_father.milestone.id)
+        else
+          expect(updates).not_to have_key(:milestone_id)
+        end
+      end
+    end
+
     shared_examples 'shrug command' do
       it 'appends ¯\_(ツ)_/¯ to the comment' do
         new_content, _ = service.execute(content, issuable)
@@ -757,6 +774,54 @@ describe QuickActions::InterpretService do
       let(:issuable) { issue }
     end
 
+    context '/inherit command' do
+      let!(:todo_label) { create(:label, project: project, title: 'To Do') }
+      let!(:inreview_label) { create(:label, project: project, title: 'In Review') }
+
+      it_behaves_like 'inherit command' do
+        # Without milestone assignment
+        let(:issue_father) { create(:labeled_issue, project: project, labels: [inreview_label, todo_label]) }
+
+        let(:content) { "/inherit #{issue_father.to_reference}" }
+        let(:issuable) { issue }
+      end
+
+      it_behaves_like 'inherit command' do
+        # With milestone assignment
+        let(:issue_father) { create(:labeled_issue, project: project, labels: [todo_label, inreview_label], milestone: milestone) }
+
+        let(:content) { "/inherit #{issue_father.to_reference(project)}" }
+        let(:issuable) { issue }
+      end
+
+      it_behaves_like 'empty command' do
+        let(:content) { '/inherit' }
+        let(:issuable) { issue }
+      end
+
+      context 'cross project references' do
+        it_behaves_like 'empty command' do
+          let(:other_project) { create(:project, :public) }
+          let(:issue_father) { create(:labeled_issue, project: other_project, labels: [todo_label, inreview_label]) }
+          let(:content) { "/inherit #{issue_father.to_reference(project)}" }
+          let(:issuable) { issue }
+        end
+
+        it_behaves_like 'empty command' do
+          let(:content) { "/inherit imaginary#1234" }
+          let(:issuable) { issue }
+        end
+
+        it_behaves_like 'empty command' do
+          let(:other_project) { create(:project, :private) }
+          let(:issue_father) { create(:issue, project: other_project) }
+
+          let(:content) { "/inherit #{issue_father.to_reference(project)}" }
+          let(:issuable) { issue }
+        end
+      end
+    end
+
     context '/duplicate command' do
       it_behaves_like 'duplicate command' do
         let(:issue_duplicate) { create(:issue, project: project) }