subscriptions support in the query planner (#2389)

* Subscriptions support in the query planner

.changeset/forty-hairs-flow.md

@@ -0,0 +1,7 @@
+---
+"@apollo/composition": minor
+"@apollo/query-planner": minor
+---
+
+Addition of new query planner node types to enable federated subscriptions support
+

composition-js/src/__tests__/compose.subscription.test.ts

@@ -0,0 +1,135 @@
+import { FEDERATION2_LINK_WITH_FULL_IMPORTS, FieldDefinition } from '@apollo/federation-internals';
+import gql from 'graphql-tag';
+import { composeServices } from '../compose';
+
+describe('subscription composition tests', () => {
+  it('type subscription appears in the supergraph', () => {
+    const subgraphA = {
+      name: 'subgraphA',
+      typeDefs: gql`
+        extend schema
+          ${FEDERATION2_LINK_WITH_FULL_IMPORTS}
+        type Query {
+          me: User!
+        }
+
+        type Subscription {
+          onNewUser: User!
+        }
+
+        type User {
+          id: ID!
+          name: String!
+        }
+      `,
+    };
+
+    const subgraphB = {
+      name: 'subgraphB',
+      typeDefs:gql`
+        extend schema
+          ${FEDERATION2_LINK_WITH_FULL_IMPORTS}
+        type Query {
+          foo: Int
+        }
+
+        type Subscription {
+          bar: Int
+        }
+    `,
+    };
+
+    const { errors, schema } = composeServices([subgraphA, subgraphB]);
+    expect(errors).toBeUndefined();
+    expect(schema).toBeDefined();
+    const onNewUser = schema?.elementByCoordinate('Subscription.onNewUser') as FieldDefinition<any>;
+    expect(onNewUser.appliedDirectives?.[0].toString()).toBe('@join__field(graph: SUBGRAPHA)');
+  });
+
+  it.each([
+    { directive: '@shareable', errorMsg: 'Fields on root level subscription object cannot be marked as shareable'},
+  ])('directives that are incompatible with subscriptions wont compose', ({ directive, errorMsg }) => {
+    const subgraphA = {
+      name: 'subgraphA',
+      typeDefs: gql`
+        extend schema
+          ${FEDERATION2_LINK_WITH_FULL_IMPORTS}
+        type Query {
+          me: User!
+        }
+
+        type Subscription {
+          onNewUser: User! ${directive}
+        }
+
+        type User {
+          id: ID!
+          name: String!
+        }
+      `,
+    };
+
+    const subgraphB = {
+      name: 'subgraphB',
+      typeDefs:gql`
+        extend schema
+          ${FEDERATION2_LINK_WITH_FULL_IMPORTS}
+        type Query {
+          foo: Int
+        }
+
+        type Subscription {
+          bar: Int
+        }
+    `,
+    };
+
+    const { errors, schema } = composeServices([subgraphA, subgraphB]);
+    expect(errors?.length).toBe(1);
+    expect(errors?.[0].message).toBe(errorMsg);
+    expect(schema).toBeUndefined();
+  });
+
+  it('subscription name collisions across subgraphs should not compose', () => {
+    const subgraphA = {
+      name: 'subgraphA',
+      typeDefs: gql`
+        extend schema
+          ${FEDERATION2_LINK_WITH_FULL_IMPORTS}
+        type Query {
+          me: User!
+        }
+
+        type Subscription {
+          onNewUser: User
+          foo: Int!
+        }
+
+        type User {
+          id: ID!
+          name: String!
+        }
+      `,
+    };
+
+    const subgraphB = {
+      name: 'subgraphB',
+      typeDefs:gql`
+        extend schema
+          ${FEDERATION2_LINK_WITH_FULL_IMPORTS}
+        type Query {
+          foo: Int
+        }
+
+        type Subscription {
+          foo: Int!
+        }
+    `,
+    };
+
+    const { errors, schema } = composeServices([subgraphA, subgraphB]);
+    expect(errors?.length).toBe(1);
+    expect(errors?.[0].message).toBe('Non-shareable field "Subscription.foo" is resolved from multiple subgraphs: it is resolved from subgraphs "subgraphA" and "subgraphB" and defined as non-shareable in all of them');
+    expect(schema).toBeUndefined();
+  });
+});

composition-js/src/merging/merge.ts

@@ -791,6 +791,7 @@ class Merger {
   private mergeObject(sources: (ObjectType | undefined)[], dest: ObjectType) {
     const isEntity = this.hintOnInconsistentEntity(sources, dest);
     const isValueType = !isEntity && !dest.isRootType();
+    const isSubscription = dest.isSubscriptionRootType();
 
     this.addFieldsShallow(sources, dest);
     if (!dest.hasFields()) {
@@ -806,7 +807,15 @@ class Merger {
         const subgraphFields = sources.map(t => t?.field(destField.name));
         const mergeContext = this.validateOverride(subgraphFields, destField);
 
-        this.mergeField(subgraphFields, destField, mergeContext);
+        if (isSubscription) {
+          this.validateSubscriptionField(subgraphFields);
+        }
+
+        this.mergeField({
+          sources: subgraphFields,
+          dest: destField,
+          mergeContext,
+        });
         this.validateFieldSharing(subgraphFields, destField, mergeContext);
       }
     }
@@ -1085,7 +1094,7 @@ class Merger {
     const { subgraphsWithOverride, subgraphMap } = sources.map((source, idx) => {
       if (!source) {
         // While the subgraph may not have the field directly, it could have "stand-in" for that field
-        // through @interfaceObject, and it is those stand-ins that would be effectively overridden. 
+        // through @interfaceObject, and it is those stand-ins that would be effectively overridden.
         const interfaceObjectAbstractingFields = this.fieldsInSourceIfAbstractedByInterfaceObject(dest, idx);
         if (interfaceObjectAbstractingFields.length > 0) {
           return {
@@ -1251,7 +1260,15 @@ class Merger {
     }).filter(isDefined);
   }
 
-  private mergeField(sources: FieldOrUndefinedArray, dest: FieldDefinition<any>, mergeContext: FieldMergeContext = new FieldMergeContext(sources)) {
+  private mergeField({
+    sources,
+    dest,
+    mergeContext = new FieldMergeContext(sources),
+  }: {
+    sources: FieldOrUndefinedArray,
+    dest: FieldDefinition<any>,
+    mergeContext: FieldMergeContext,
+  }) {
     if (sources.every((s, i) => s === undefined ? this.fieldsInSourceIfAbstractedByInterfaceObject(dest, i).every((f) => this.isExternal(i, f)) : this.isExternal(i, s))) {
       const definingSubgraphs = sources.map((source, i) => {
         if (source) {
@@ -1790,7 +1807,11 @@ class Merger {
       }
       const subgraphFields = sources.map(t => t?.field(destField.name));
       const mergeContext = this.validateOverride(subgraphFields, destField);
-      this.mergeField(subgraphFields, destField, mergeContext);
+      this.mergeField({
+        sources: subgraphFields,
+        dest: destField,
+        mergeContext,
+      });
     }
   }
 
@@ -2805,4 +2826,16 @@ class Merger {
         : err;
     });
   }
+
+  private validateSubscriptionField(sources: FieldOrUndefinedArray) {
+    // no subgraph marks field as @shareable
+    const fieldsWithShareable = sources.filter((src, idx) => src && src.appliedDirectivesOf(this.metadata(idx).shareableDirective()).length > 0);
+    if (fieldsWithShareable.length > 0) {
+      const nodes = sourceASTs(...fieldsWithShareable);
+      this.errors.push(ERRORS.INVALID_FIELD_SHARING.err(
+        `Fields on root level subscription object cannot be marked as shareable`,
+        { nodes},
+      ));
+    }
+  }
 }

federation-integration-testsuite-js/src/matchers/toCallService.ts

@@ -1,4 +1,4 @@
-import { QueryPlan, PlanNode } from '@apollo/query-planner';
+import { QueryPlan, PlanNode, SubscriptionNode } from '@apollo/query-planner';
 import { astSerializer, queryPlanSerializer } from '../snapshotSerializers';
 import prettyFormat from 'pretty-format';
 
@@ -41,9 +41,9 @@ function toCallService(
   let pass = false;
   // let initialServiceCall = null;
   // recurse the node, find first match of service name, return
-  function walkExecutionNode(node?: PlanNode) {
+  function walkExecutionNode(node?: PlanNode | SubscriptionNode) {
     if (!node) return;
-    if (node.kind === 'Fetch' && node.serviceName === service) {
+    if ((node.kind === 'Fetch') && node.serviceName === service) {
       pass = true;
       // initialServiceCall = node;
       return;
@@ -56,6 +56,10 @@ function toCallService(
       case 'Sequence':
         node.nodes.forEach(walkExecutionNode);
         break;
+      case 'Subscription':
+        walkExecutionNode(node.primary);
+        walkExecutionNode(node.rest);
+        break;
       default:
         return;
     }

gateway-js/src/executeQueryPlan.ts

@@ -129,6 +129,10 @@ export async function executeQueryPlan(
           requestContext.metrics && requestContext.metrics.captureTraces
       );
 
+      if (queryPlan.node?.kind === 'Subscription') {
+        throw new Error('Execution of subscriptions not supported by gateway');
+      }
+
       if (queryPlan.node) {
         const traceNode = await executeNode(
           context,

internals-js/src/definitions.ts

@@ -2091,6 +2091,14 @@ export class ObjectType extends FieldBasedType<ObjectType, ObjectTypeReferencer>
     return schema.schemaDefinition.root('query')?.type === this;
   }
 
+  /**
+   *  Whether this type is the "subscription" root type of the schema (will return false if the type is detached).
+   */
+  isSubscriptionRootType(): boolean {
+    const schema = this.schema();
+    return schema.schemaDefinition.root('subscription')?.type === this;
+  }
+
   protected removeReferenceRecursive(ref: ObjectTypeReferencer): void {
     // Note that the ref can also be a`SchemaDefinition`, but don't have anything to do then.
     switch (ref.kind) {

query-planner-js/src/QueryPlan.ts

@@ -11,7 +11,7 @@ export type ResponsePath = (string | number)[];
 
 export interface QueryPlan {
   kind: 'QueryPlan';
-  node?: PlanNode;
+  node?: PlanNode | SubscriptionNode;
 }
 
 export type PlanNode = SequenceNode | ParallelNode | FetchNode | FlattenNode | DeferNode | ConditionNode;
@@ -26,6 +26,12 @@ export interface ParallelNode {
   nodes: PlanNode[];
 }
 
+export interface SubscriptionNode {
+  kind: 'Subscription';
+  primary: FetchNode;
+  rest?: PlanNode;
+}
+
 export interface FetchNode {
   kind: 'Fetch';
   serviceName: string;
@@ -229,3 +235,7 @@ export const trimSelectionNodes = (
 
   return remapped;
 };
+
+export const isPlanNode = (node: PlanNode | SubscriptionNode | undefined): node is PlanNode => {
+  return !!node && node.kind !== 'Subscription';
+}

query-planner-js/src/__tests__/buildPlan.interfaceObject.test.ts

@@ -1,5 +1,6 @@
-import { operationFromDocument } from '@apollo/federation-internals';
+import { assert, operationFromDocument } from '@apollo/federation-internals';
 import gql from 'graphql-tag';
+import { isPlanNode } from '../QueryPlan';
 import { composeAndCreatePlanner, findFetchNodes } from "./testHelper";
 
 describe('basic @key on interface/@interfaceObject handling', () => {
@@ -306,6 +307,7 @@ describe('basic @key on interface/@interfaceObject handling', () => {
       }
     `);
 
+    assert(isPlanNode(plan.node), 'buildQueryPlan should return QueryPlan');
     const rewrites = findFetchNodes('S2', plan.node)[0].inputRewrites;
     expect(rewrites).toBeDefined();
     expect(rewrites?.length).toBe(1);