Allow null as an acceptable value for issue weight in GraphQL API

doc/api/graphql/reference/index.md

@@ -2548,7 +2548,7 @@ Input type: `IssueSetWeightInput`
 | <a id="mutationissuesetweightclientmutationid"></a>`clientMutationId` | [`String`](#string) | A unique identifier for the client performing the mutation. |
 | <a id="mutationissuesetweightiid"></a>`iid` | [`String!`](#string) | The IID of the issue to mutate. |
 | <a id="mutationissuesetweightprojectpath"></a>`projectPath` | [`ID!`](#id) | The project the issue to mutate is in. |
-| <a id="mutationissuesetweightweight"></a>`weight` | [`Int!`](#int) | The desired weight for the issue. |
+| <a id="mutationissuesetweightweight"></a>`weight` | [`Int`](#int) | The desired weight for the issue. If set to null, weight is removed. |
 
 #### Fields
 

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

@@ -7,8 +7,17 @@ module Mutations
 
       argument :weight,
                GraphQL::INT_TYPE,
-               required: true,
-               description: 'The desired weight for the issue.'
+               required: false,
+               description: 'The desired weight for the issue. ' \
+               'If set to null, weight is removed.'
+
+      def ready?(**args)
+        unless args.key?(:weight)
+          raise Gitlab::Graphql::Errors::ArgumentError, 'The `weight` argument is required (`null` accepted).'
+        end
+
+        super
+      end
 
       def resolve(project_path:, iid:, weight:)
         issue = authorized_find!(project_path: project_path, iid: iid)

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

@@ -2,7 +2,7 @@
 require 'spec_helper'
 
 RSpec.describe Mutations::Issues::SetWeight do
-  let(:issue) { create(:issue) }
+  let(:issue) { create(:issue, weight: 1) }
   let(:user) { create(:user) }
 
   subject(:mutation) { described_class.new(object: nil, context: { current_user: user }, field: nil) }
@@ -20,11 +20,19 @@ RSpec.describe Mutations::Issues::SetWeight do
         issue.project.add_developer(user)
       end
 
-      it 'returns the issue with correct weight' do
+      it 'returns the issue with correct weight', :aggregate_failures do
         expect(mutated_issue).to eq(issue)
         expect(mutated_issue.weight).to eq(2)
         expect(subject[:errors]).to be_empty
       end
+
+      context 'when the weight is nil' do
+        let(:weight) { nil }
+
+        it 'updates weight to be nil' do
+          expect(mutated_issue.weight).to be nil
+        end
+      end
     end
   end
 end

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

@@ -6,7 +6,7 @@ RSpec.describe 'Setting weight of an issue' do
   include GraphqlHelpers
 
   let(:current_user) { create(:user) }
-  let(:issue) { create(:issue) }
+  let(:issue) { create(:issue, weight: 1) }
   let(:project) { issue.project }
   let(:input) { { weight: 2 } }
 
@@ -44,12 +44,35 @@ RSpec.describe 'Setting weight of an issue' do
     expect(graphql_errors).to include(a_hash_including('message' => error))
   end
 
+  context 'when weight is a number' do
     it 'updates the issue weight' do
       post_graphql_mutation(mutation, current_user: current_user)
 
       expect(response).to have_gitlab_http_status(:success)
       expect(mutation_response['issue']['weight']).to eq(2)
     end
+  end
+
+  context 'when weight is null' do
+    let(:input) { { weight: nil } }
+
+    it 'updates the issue weight' do
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(mutation_response['issue']['weight']).to eq(nil)
+    end
+  end
+
+  context 'when weight is not given' do
+    let(:input) { {} }
+
+    it 'returns an error' do
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(graphql_errors).to include(a_hash_including('message' => /The `weight` argument is required \(`null` accepted\)/))
+    end
+  end
 
   context 'when weight is not an integer' do
     let(:input) { { weight: "2" } }