GraphQL: Add MRSetMilestone mutation

Add a mutation to set or remove a milestone on a Merge Request

app/graphql/gitlab_schema.rb

@@ -46,7 +46,7 @@ class GitlabSchema < GraphQL::Schema
       super(query_str, **kwargs)
     end
 
-    def id_from_object(object)
+    def id_from_object(object, _type = nil, _ctx = nil)
       unless object.respond_to?(:to_global_id)
         # This is an error in our schema and needs to be solved. So raise a
         # more meaningful error message
@@ -57,7 +57,7 @@ class GitlabSchema < GraphQL::Schema
       object.to_global_id
     end
 
-    def object_from_id(global_id)
+    def object_from_id(global_id, _ctx = nil)
       gid = GlobalID.parse(global_id)
 
       unless gid

app/graphql/mutations/merge_requests/set_milestone.rb

+# frozen_string_literal: true
+
+module Mutations
+  module MergeRequests
+    class SetMilestone < Base
+      graphql_name 'MergeRequestSetMilestone'
+
+      argument :milestone_id,
+               GraphQL::ID_TYPE,
+               required: false,
+               loads: Types::MilestoneType,
+               description: <<~DESC
+                            The milestone to assign to the merge request.
+               DESC
+
+      def resolve(project_path:, iid:, milestone: nil)
+        merge_request = authorized_find!(project_path: project_path, iid: iid)
+        project = merge_request.project
+
+        ::MergeRequests::UpdateService.new(project, current_user, milestone: milestone)
+          .execute(merge_request)
+
+        {
+          merge_request: merge_request,
+          errors: merge_request.errors.full_messages
+        }
+      end
+    end
+  end
+end

app/graphql/types/milestone_type.rb

@@ -6,6 +6,8 @@ module Types
 
     authorize :read_milestone
 
+    field :id, GraphQL::ID_TYPE, null: false,
+          description: 'ID of the milestone'
     field :description, GraphQL::STRING_TYPE, null: true,
           description: 'Description of the milestone'
     field :title, GraphQL::STRING_TYPE, null: false,

app/graphql/types/mutation_type.rb

@@ -9,6 +9,7 @@ module Types
     mount_mutation Mutations::AwardEmojis::Add
     mount_mutation Mutations::AwardEmojis::Remove
     mount_mutation Mutations::AwardEmojis::Toggle
+    mount_mutation Mutations::MergeRequests::SetMilestone
     mount_mutation Mutations::MergeRequests::SetWip, calls_gitaly: true
     mount_mutation Mutations::Notes::Create::Note, calls_gitaly: true
     mount_mutation Mutations::Notes::Create::DiffNote, calls_gitaly: true

changelogs/unreleased/31919-graphql-MR-sidebar-mutations.yml

+---
+title: 'GraphQL: Add Merge Request milestone mutation'
+merge_request: 19257
+author:
+type: added

doc/api/graphql/reference/index.md

@@ -473,6 +473,14 @@ The API can be explored interactively using the [GraphiQL IDE](../index.md#graph
 | `cherryPickOnCurrentMergeRequest` | Boolean! | Whether or not a user can perform `cherry_pick_on_current_merge_request` on this resource |
 | `revertOnCurrentMergeRequest` | Boolean! | Whether or not a user can perform `revert_on_current_merge_request` on this resource |
 
+### MergeRequestSetMilestonePayload
+
+| Name  | Type  | Description |
+| ---   |  ---- | ----------  |
+| `clientMutationId` | String | A unique identifier for the client performing the mutation. |
+| `errors` | String! => Array | Reasons why the mutation failed. |
+| `mergeRequest` | MergeRequest | The merge request after mutation |
+
 ### MergeRequestSetWipPayload
 
 | Name  | Type  | Description |
@@ -492,6 +500,7 @@ The API can be explored interactively using the [GraphiQL IDE](../index.md#graph
 
 | Name  | Type  | Description |
 | ---   |  ---- | ----------  |
+| `id` | ID! | ID of the milestone |
 | `description` | String | Description of the milestone |
 | `title` | String! | Title of the milestone |
 | `state` | String! | State of the milestone |

spec/graphql/mutations/merge_requests/set_milestone_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Mutations::MergeRequests::SetMilestone do
+  let(:merge_request) { create(:merge_request) }
+  let(:user) { create(:user) }
+  subject(:mutation) { described_class.new(object: nil, context: { current_user: user }) }
+
+  describe '#resolve' do
+    let(:milestone) { create(:milestone, project: merge_request.project) }
+    let(:mutated_merge_request) { subject[:merge_request] }
+    subject { mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, milestone: milestone) }
+
+    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 merge request' do
+      before do
+        merge_request.project.add_developer(user)
+      end
+
+      it 'returns the merge request with the milestone' do
+        expect(mutated_merge_request).to eq(merge_request)
+        expect(mutated_merge_request.milestone).to eq(milestone)
+        expect(subject[:errors]).to be_empty
+      end
+
+      it 'returns errors merge request could not be updated' do
+        # Make the merge request invalid
+        merge_request.allow_broken = true
+        merge_request.update!(source_project: nil)
+
+        expect(subject[:errors]).not_to be_empty
+      end
+
+      context 'when passing milestone_id as nil' do
+        let(:milestone) { nil }
+
+        it 'removes the milestone' do
+          merge_request.update!(milestone: create(:milestone, project: merge_request.project))
+
+          expect(mutated_merge_request.milestone).to eq(nil)
+        end
+
+        it 'does not do anything if the MR already does not have a milestone' do
+          expect(mutated_merge_request.milestone).to eq(nil)
+        end
+      end
+    end
+  end
+end

spec/requests/api/graphql/mutations/merge_requests/set_milestone_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Setting milestone of a merge request' do
+  include GraphqlHelpers
+
+  let(:current_user) { create(:user) }
+  let(:merge_request) { create(:merge_request) }
+  let(:project) { merge_request.project }
+  let(:milestone) { create(:milestone, project: project) }
+  let(:input) { { milestone_id: GitlabSchema.id_from_object(milestone).to_s } }
+
+  let(:mutation) do
+    variables = {
+      project_path: project.full_path,
+      iid: merge_request.iid.to_s
+    }
+    graphql_mutation(:merge_request_set_milestone, variables.merge(input),
+                     <<-QL.strip_heredoc
+                       clientMutationId
+                       errors
+                       mergeRequest {
+                         id
+                         milestone {
+                           id
+                         }
+                       }
+                     QL
+    )
+  end
+
+  def mutation_response
+    graphql_mutation_response(:merge_request_set_milestone)
+  end
+
+  before do
+    project.add_developer(current_user)
+  end
+
+  it 'returns an error if the user is not allowed to update the merge request' do
+    post_graphql_mutation(mutation, current_user: create(:user))
+
+    expect(graphql_errors).not_to be_empty
+  end
+
+  it 'sets the merge request milestone' do
+    post_graphql_mutation(mutation, current_user: current_user)
+
+    expect(response).to have_gitlab_http_status(:success)
+    expect(mutation_response['mergeRequest']['milestone']['id']).to eq(milestone.to_global_id.to_s)
+  end
+
+  context 'when passing milestone_id nil as input' do
+    let(:input) { { milestone_id: nil } }
+
+    it 'removes the merge request milestone' do
+      merge_request.update!(milestone: milestone)
+
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(mutation_response['mergeRequest']['milestone']).to be_nil
+    end
+  end
+end