Add GraphQL mutation to set the epic of an issue

- Add tests
- Udpate doscumentationa and schema

Add test case where issue can not be updated

doc/api/graphql/reference/gitlab_schema.graphql

@@ -6732,6 +6732,51 @@ type IssueSetDueDatePayload {
   issue: Issue
 }
 
+"""
+Autogenerated input type of IssueSetEpic
+"""
+input IssueSetEpicInput {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  Global ID of the epic to be assigned to the issue
+  """
+  epicId: ID!
+
+  """
+  The IID of the issue to mutate
+  """
+  iid: String!
+
+  """
+  The project the issue to mutate is in
+  """
+  projectPath: ID!
+}
+
+"""
+Autogenerated return type of IssueSetEpic
+"""
+type IssueSetEpicPayload {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  Errors encountered during execution of the mutation.
+  """
+  errors: [String!]!
+
+  """
+  The issue after mutation
+  """
+  issue: Issue
+}
+
 """
 Autogenerated input type of IssueSetIteration
 """
@@ -8802,6 +8847,7 @@ type Mutation {
   issueSetAssignees(input: IssueSetAssigneesInput!): IssueSetAssigneesPayload
   issueSetConfidential(input: IssueSetConfidentialInput!): IssueSetConfidentialPayload
   issueSetDueDate(input: IssueSetDueDateInput!): IssueSetDueDatePayload
+  issueSetEpic(input: IssueSetEpicInput!): IssueSetEpicPayload
   issueSetIteration(input: IssueSetIterationInput!): IssueSetIterationPayload
   issueSetLocked(input: IssueSetLockedInput!): IssueSetLockedPayload
   issueSetSubscription(input: IssueSetSubscriptionInput!): IssueSetSubscriptionPayload

doc/api/graphql/reference/gitlab_schema.json

@@ -18678,6 +18678,136 @@
           "enumValues": null,
           "possibleTypes": null
         },
+        {
+          "kind": "INPUT_OBJECT",
+          "name": "IssueSetEpicInput",
+          "description": "Autogenerated input type of IssueSetEpic",
+          "fields": null,
+          "inputFields": [
+            {
+              "name": "projectPath",
+              "description": "The project the issue to mutate is in",
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "SCALAR",
+                  "name": "ID",
+                  "ofType": null
+                }
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "iid",
+              "description": "The IID of the issue to mutate",
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "SCALAR",
+                  "name": "String",
+                  "ofType": null
+                }
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "epicId",
+              "description": "Global ID of the epic to be assigned to the issue",
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "SCALAR",
+                  "name": "ID",
+                  "ofType": null
+                }
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "clientMutationId",
+              "description": "A unique identifier for the client performing the mutation.",
+              "type": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              },
+              "defaultValue": null
+            }
+          ],
+          "interfaces": null,
+          "enumValues": null,
+          "possibleTypes": null
+        },
+        {
+          "kind": "OBJECT",
+          "name": "IssueSetEpicPayload",
+          "description": "Autogenerated return type of IssueSetEpic",
+          "fields": [
+            {
+              "name": "clientMutationId",
+              "description": "A unique identifier for the client performing the mutation.",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
+            {
+              "name": "errors",
+              "description": "Errors encountered during execution of the mutation.",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "LIST",
+                  "name": null,
+                  "ofType": {
+                    "kind": "NON_NULL",
+                    "name": null,
+                    "ofType": {
+                      "kind": "SCALAR",
+                      "name": "String",
+                      "ofType": null
+                    }
+                  }
+                }
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
+            {
+              "name": "issue",
+              "description": "The issue after mutation",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "OBJECT",
+                "name": "Issue",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            }
+          ],
+          "inputFields": null,
+          "interfaces": [
+
+          ],
+          "enumValues": null,
+          "possibleTypes": null
+        },
         {
           "kind": "INPUT_OBJECT",
           "name": "IssueSetIterationInput",
@@ -25604,6 +25734,33 @@
               "isDeprecated": false,
               "deprecationReason": null
             },
+            {
+              "name": "issueSetEpic",
+              "description": null,
+              "args": [
+                {
+                  "name": "input",
+                  "description": null,
+                  "type": {
+                    "kind": "NON_NULL",
+                    "name": null,
+                    "ofType": {
+                      "kind": "INPUT_OBJECT",
+                      "name": "IssueSetEpicInput",
+                      "ofType": null
+                    }
+                  },
+                  "defaultValue": null
+                }
+              ],
+              "type": {
+                "kind": "OBJECT",
+                "name": "IssueSetEpicPayload",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
             {
               "name": "issueSetIteration",
               "description": null,

doc/api/graphql/reference/index.md

@@ -1019,6 +1019,16 @@ Autogenerated return type of IssueSetDueDate
 | `errors` | String! => Array | Errors encountered during execution of the mutation. |
 | `issue` | Issue | The issue after mutation |
 
+## IssueSetEpicPayload
+
+Autogenerated return type of IssueSetEpic
+
+| Name  | Type  | Description |
+| ---   |  ---- | ----------  |
+| `clientMutationId` | String | A unique identifier for the client performing the mutation. |
+| `errors` | String! => Array | Errors encountered during execution of the mutation. |
+| `issue` | Issue | The issue after mutation |
+
 ## IssueSetIterationPayload
 
 Autogenerated return type of IssueSetIteration

ee/app/graphql/ee/types/mutation_type.rb

@@ -8,6 +8,7 @@ module EE
       prepended do
         mount_mutation ::Mutations::Issues::SetIteration
         mount_mutation ::Mutations::Issues::SetWeight
+        mount_mutation ::Mutations::Issues::SetEpic
         mount_mutation ::Mutations::EpicTree::Reorder
         mount_mutation ::Mutations::Epics::Update
         mount_mutation ::Mutations::Epics::Create

ee/app/graphql/mutations/issues/set_epic.rb

+# frozen_string_literal: true
+
+module Mutations
+  module Issues
+    class SetEpic < Base
+      graphql_name 'IssueSetEpic'
+
+      argument :epic_id,
+               GraphQL::ID_TYPE,
+               required: true,
+               loads: Types::EpicType,
+               description: 'Global ID of the epic to be assigned to the issue'
+
+      def resolve(project_path:, iid:, epic: nil)
+        issue = authorized_find!(project_path: project_path, iid: iid)
+        project = issue.project
+
+        authorize_admin_rights!(epic)
+
+        ::Issues::UpdateService.new(project, current_user, epic: epic)
+          .execute(issue)
+
+        {
+          issue: issue,
+          errors: issue.errors.full_messages
+        }
+      end
+
+      private
+
+      def authorize_admin_rights!(epic)
+        return unless epic.present?
+
+        raise_resource_not_available_error! unless Ability.allowed?(current_user, :admin_epic, epic.group)
+      end
+    end
+  end
+end

ee/changelogs/unreleased/229506-graphql-mutation-for-adding-epic-to-issue.yml

+---
+title: Add GraphQL mutation to set the epic of an issue
+merge_request: 38494
+author:
+type: added

ee/spec/graphql/mutations/issues/set_epic_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Mutations::Issues::SetEpic do
+  let_it_be(:group) { create(:group) }
+  let_it_be(:project) { create(:project, group: group) }
+  let_it_be(:user) { create(:user) }
+  let_it_be_with_reload(:issue) { create(:issue, project: project) }
+
+  subject(:mutation) { described_class.new(object: nil, context: { current_user: user }, field: nil) }
+
+  describe '#resolve' do
+    let_it_be_with_reload(:epic) { create(:epic, group: group) }
+    let(:mutated_issue) { subject[:issue] }
+
+    subject { mutation.resolve(project_path: issue.project.full_path, iid: issue.iid, epic: epic) }
+
+    it 'raises an error if the resource is not accessible to the user' do
+      expect { subject }.to raise_error(Gitlab::Graphql::Errors::ResourceNotAvailable)
+    end
+
+    context 'when the user can update the issue' do
+      before do
+        stub_licensed_features(epics: true)
+        project.add_developer(user)
+      end
+
+      it 'raises an error if the epic is not accessible to the user' do
+        expect { subject }.to raise_error(Gitlab::Graphql::Errors::ResourceNotAvailable)
+      end
+
+      context 'when user can admin epic' do
+        before do
+          group.add_owner(user)
+        end
+
+        it 'returns the issue with the epic' do
+          expect(mutated_issue).to eq(issue)
+          expect(mutated_issue.epic).to eq(epic)
+          expect(subject[:errors]).to be_empty
+        end
+
+        it 'returns errors if issue could not be updated' do
+          issue.update_column(:author_id, nil)
+
+          expect(subject[:errors]).to eq(["Author can't be blank"])
+        end
+
+        context 'when passing epic_id as nil' do
+          let(:epic) { nil }
+
+          it 'removes the epic' do
+            issue.update!(epic: create(:epic, group: group))
+
+            expect(mutated_issue.epic).to eq(nil)
+          end
+
+          it 'does not do anything if the issue already does not have a epic' do
+            expect(mutated_issue.epic).to eq(nil)
+          end
+        end
+      end
+    end
+  end
+end

ee/spec/requests/api/graphql/mutations/issues/set_epic_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'Setting the epic of an issue' do
+  include GraphqlHelpers
+
+  let(:current_user) { create(:user) }
+  let(:group) { create(:group) }
+  let(:epic) { create(:epic, group: group) }
+  let(:project) { create(:project, group: group) }
+  let(:issue) { create(:issue, project: project) }
+  let(:input) { { epic_id: global_id_of(epic) } }
+
+  let(:mutation) do
+    graphql_mutation(
+      :issue_set_epic,
+      { project_path: project.full_path, iid: issue.iid.to_s }.merge(input),
+      <<~GRAPHQL
+        clientMutationId
+        errors
+        issue {
+          iid
+          epic {
+            iid
+            title
+          }
+        }
+      GRAPHQL
+    )
+  end
+
+  def mutation_response
+    graphql_mutation_response(:issue_set_epic)
+  end
+
+  before do
+    project.add_developer(current_user)
+    group.add_developer(current_user)
+    stub_licensed_features(epics: true)
+  end
+
+  it 'returns an error if the user is not allowed to update the issue' do
+    error = "The resource that you are attempting to access does not exist or you "\
+            "don't have permission to perform this action"
+
+    post_graphql_mutation(mutation, current_user: create(:user))
+
+    expect(graphql_errors).to include(a_hash_including('message' => error))
+  end
+
+  it 'return an error if issue can not be updated' do
+    issue.update_column(:author_id, nil)
+    post_graphql_mutation(mutation, current_user: current_user)
+
+    expect(mutation_response["errors"]).to eq(["Author can't be blank"])
+  end
+
+  it 'sets given epic to the issue' do
+    post_graphql_mutation(mutation, current_user: current_user)
+
+    expect(response).to have_gitlab_http_status(:success)
+    expect(mutation_response['errors']).to be_empty
+    expect(mutation_response['issue']['epic']['iid']).to eq(epic.iid.to_s)
+    expect(mutation_response['issue']['epic']['title']).to eq(epic.title)
+    expect(issue.reload.epic).to eq(epic)
+  end
+end