Add epic filter for issues GraphQL

It can be used for Issues Analytics

app/graphql/resolvers/concerns/issue_resolver_arguments.rb

@@ -29,7 +29,7 @@ module IssueResolverArguments
               description: 'Usernames of users assigned to the issue'
     argument :assignee_id, GraphQL::STRING_TYPE,
               required: false,
-              description: 'ID of a user assigned to the issues, "none" and "any" values supported'
+              description: 'ID of a user assigned to the issues, "none" and "any" values are supported'
     argument :created_before, Types::TimeType,
               required: false,
               description: 'Issues created before this date'

doc/api/graphql/reference/gitlab_schema.graphql

@@ -8387,7 +8387,7 @@ type Group {
     after: String
 
     """
-    ID of a user assigned to the issues, "none" and "any" values supported
+    ID of a user assigned to the issues, "none" and "any" values are supported
     """
     assigneeId: String
 
@@ -8431,6 +8431,11 @@ type Group {
     """
     createdBefore: Time
 
+    """
+    ID of an epic associated with the issues, "none" and "any" values are supported
+    """
+    epicId: String
+
     """
     Returns the first _n_ elements from the list.
     """
@@ -14695,7 +14700,7 @@ type Project {
   """
   issue(
     """
-    ID of a user assigned to the issues, "none" and "any" values supported
+    ID of a user assigned to the issues, "none" and "any" values are supported
     """
     assigneeId: String
 
@@ -14734,6 +14739,11 @@ type Project {
     """
     createdBefore: Time
 
+    """
+    ID of an epic associated with the issues, "none" and "any" values are supported
+    """
+    epicId: String
+
     """
     IID of the issue. For example, "1"
     """
@@ -14795,7 +14805,7 @@ type Project {
   """
   issueStatusCounts(
     """
-    ID of a user assigned to the issues, "none" and "any" values supported
+    ID of a user assigned to the issues, "none" and "any" values are supported
     """
     assigneeId: String
 
@@ -14885,7 +14895,7 @@ type Project {
     after: String
 
     """
-    ID of a user assigned to the issues, "none" and "any" values supported
+    ID of a user assigned to the issues, "none" and "any" values are supported
     """
     assigneeId: String
 
@@ -14929,6 +14939,11 @@ type Project {
     """
     createdBefore: Time
 
+    """
+    ID of an epic associated with the issues, "none" and "any" values are supported
+    """
+    epicId: String
+
     """
     Returns the first _n_ elements from the list.
     """

doc/api/graphql/reference/gitlab_schema.json

@@ -23095,7 +23095,7 @@
                 },
                 {
                   "name": "assigneeId",
-                  "description": "ID of a user assigned to the issues, \"none\" and \"any\" values supported",
+                  "description": "ID of a user assigned to the issues, \"none\" and \"any\" values are supported",
                   "type": {
                     "kind": "SCALAR",
                     "name": "String",
@@ -23225,6 +23225,16 @@
                   },
                   "defaultValue": null
                 },
+                {
+                  "name": "epicId",
+                  "description": "ID of an epic associated with the issues, \"none\" and \"any\" values are supported",
+                  "type": {
+                    "kind": "SCALAR",
+                    "name": "String",
+                    "ofType": null
+                  },
+                  "defaultValue": null
+                },
                 {
                   "name": "includeSubgroups",
                   "description": "Include issues belonging to subgroups",
@@ -43209,7 +43219,7 @@
                 },
                 {
                   "name": "assigneeId",
-                  "description": "ID of a user assigned to the issues, \"none\" and \"any\" values supported",
+                  "description": "ID of a user assigned to the issues, \"none\" and \"any\" values are supported",
                   "type": {
                     "kind": "SCALAR",
                     "name": "String",
@@ -43338,6 +43348,16 @@
                     }
                   },
                   "defaultValue": null
+                },
+                {
+                  "name": "epicId",
+                  "description": "ID of an epic associated with the issues, \"none\" and \"any\" values are supported",
+                  "type": {
+                    "kind": "SCALAR",
+                    "name": "String",
+                    "ofType": null
+                  },
+                  "defaultValue": null
                 }
               ],
               "type": {
@@ -43448,7 +43468,7 @@
                 },
                 {
                   "name": "assigneeId",
-                  "description": "ID of a user assigned to the issues, \"none\" and \"any\" values supported",
+                  "description": "ID of a user assigned to the issues, \"none\" and \"any\" values are supported",
                   "type": {
                     "kind": "SCALAR",
                     "name": "String",
@@ -43653,7 +43673,7 @@
                 },
                 {
                   "name": "assigneeId",
-                  "description": "ID of a user assigned to the issues, \"none\" and \"any\" values supported",
+                  "description": "ID of a user assigned to the issues, \"none\" and \"any\" values are supported",
                   "type": {
                     "kind": "SCALAR",
                     "name": "String",
@@ -43783,6 +43803,16 @@
                   },
                   "defaultValue": null
                 },
+                {
+                  "name": "epicId",
+                  "description": "ID of an epic associated with the issues, \"none\" and \"any\" values are supported",
+                  "type": {
+                    "kind": "SCALAR",
+                    "name": "String",
+                    "ofType": null
+                  },
+                  "defaultValue": null
+                },
                 {
                   "name": "after",
                   "description": "Returns the elements in the list that come after the specified cursor.",

ee/app/graphql/ee/resolvers/issues_resolver.rb

@@ -10,6 +10,10 @@ module EE
         argument :iteration_id, ::GraphQL::ID_TYPE.to_list_type,
                  required: false,
                  description: 'Iterations applied to the issue'
+
+        argument :epic_id, GraphQL::STRING_TYPE,
+                 required: false,
+                 description: 'ID of an epic associated with the issues, "none" and "any" values are supported'
       end
 
       private

ee/spec/graphql/ee/resolvers/issues_resolver_spec.rb

@@ -7,7 +7,7 @@ RSpec.describe Resolvers::IssuesResolver do
 
   let_it_be(:current_user) { create(:user) }
   let_it_be(:group) { create(:group) }
-  let_it_be(:project) { create(:project, namespace: group) }
+  let_it_be(:project) { create(:project, namespace: group, skip_disk_validation: true) }
 
   context "with a project" do
     describe '#resolve' do
@@ -72,6 +72,26 @@ RSpec.describe Resolvers::IssuesResolver do
           expect(resolve_issues(iteration_id: iteration1.id)).to eq [issue_with_iteration]
         end
       end
+
+      describe 'filter by epic' do
+        let_it_be(:epic) { create :epic, group: group }
+        let_it_be(:epic2) { create :epic, group: group }
+        let_it_be(:issue1) { create :issue, project: project, epic: epic }
+        let_it_be(:issue2) { create :issue, project: project, epic: epic2 }
+        let_it_be(:issue3) { create :issue, project: project }
+
+        it 'returns issues without epic when epic_id is "none"' do
+          expect(resolve_issues(epic_id: 'none')).to match_array([issue3])
+        end
+
+        it 'returns issues with any epic when epic_id is "any"' do
+          expect(resolve_issues(epic_id: 'any')).to match_array([issue1, issue2])
+        end
+
+        it 'returns issues with any epic when epic_id is specific' do
+          expect(resolve_issues(epic_id: epic.id)).to match_array([issue1])
+        end
+      end
     end
   end