Fix handling of aliases and variables in introspection queries

.changeset/itchy-ants-lay.md

@@ -0,0 +1,6 @@
+---
+"@apollo/gateway": patch
+---
+
+Fix handling of aliases and variables in introspection queries.
+

gateway-js/src/__tests__/executeQueryPlan.introspection.test.ts

@@ -0,0 +1,140 @@
+import gql from 'graphql-tag';
+import { getFederatedTestingSchema, ServiceDefinitionModule } from './execution-utils';
+import { Operation, parseOperation, Schema } from "@apollo/federation-internals";
+import { QueryPlan } from '@apollo/query-planner';
+import { LocalGraphQLDataSource } from '../datasources';
+import { GatewayExecutionResult, GatewayGraphQLRequestContext } from '@apollo/server-gateway-interface';
+import { buildOperationContext } from '../operationContext';
+import { executeQueryPlan } from '../executeQueryPlan';
+
+function buildRequestContext(variables: Record<string, any>): GatewayGraphQLRequestContext {
+  // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+  // @ts-ignore
+  return {
+    cache: undefined as any,
+    context: {},
+    request: {
+      variables,
+    },
+    metrics: {},
+  };
+}
+
+async function executePlan(
+  queryPlan: QueryPlan,
+  operation: Operation,
+  schema: Schema,
+  serviceMap: { [serviceName: string]: LocalGraphQLDataSource },
+  variables: Record<string, any> = {},
+): Promise<GatewayExecutionResult> {
+  const apiSchema = schema.toAPISchema();
+  const operationContext = buildOperationContext({
+    schema: apiSchema.toGraphQLJSSchema(),
+    operationDocument: gql`${operation.toString()}`,
+  });
+  return executeQueryPlan(
+    queryPlan,
+    serviceMap,
+    buildRequestContext(variables),
+    operationContext,
+    schema.toGraphQLJSSchema(),
+    apiSchema,
+  );
+}
+
+describe('handling of introspection queries', () => {
+  const typeDefs: ServiceDefinitionModule[] = [
+    {
+      name: 'S1',
+      typeDefs: gql`
+        type Query {
+          t: [T]
+        }
+
+        interface T {
+          id: ID!
+        }
+
+        type T1 implements T @key(fields: "id") {
+          id: ID!
+          a1: Int
+        }
+
+        type T2 implements T @key(fields: "id") {
+          id: ID!
+          a2: Int
+        }
+      `,
+    },
+  ];
+  const { serviceMap, schema, queryPlanner} = getFederatedTestingSchema(typeDefs);
+
+  it('it handles aliases on introspection fields', async () => {
+    const operation = parseOperation(schema, `
+      {
+        myAlias: __type(name: "T1") {
+          kind
+          name
+        }
+      }
+    `);
+
+    const queryPlan = queryPlanner.buildQueryPlan(operation);
+    const response = await executePlan(queryPlan, operation, schema, serviceMap);
+    expect(response.errors).toBeUndefined();
+    expect(response.data).toMatchInlineSnapshot(`
+      Object {
+        "myAlias": Object {
+          "kind": "OBJECT",
+          "name": "T1",
+        },
+      }
+    `);
+  });
+
+  it('it handles aliases inside introspection fields', async () => {
+    const operation = parseOperation(schema, `
+      {
+        __type(name: "T1") {
+          myKind: kind
+          name
+        }
+      }
+    `);
+
+    const queryPlan = queryPlanner.buildQueryPlan(operation);
+    const response = await executePlan(queryPlan, operation, schema, serviceMap);
+    expect(response.errors).toBeUndefined();
+    expect(response.data).toMatchInlineSnapshot(`
+      Object {
+        "__type": Object {
+          "myKind": "OBJECT",
+          "name": "T1",
+        },
+      }
+    `);
+  });
+
+  it('it handles variables passed to introspection fields', async () => {
+    const operation = parseOperation(schema, `
+      query ($name: String!) {
+        __type(name: $name) {
+          kind
+          name
+        }
+      }
+    `);
+
+    const queryPlan = queryPlanner.buildQueryPlan(operation);
+    const response = await executePlan(queryPlan, operation, schema, serviceMap, { name: "T1" });
+    expect(response.errors).toBeUndefined();
+    expect(response.data).toMatchInlineSnapshot(`
+      Object {
+        "__type": Object {
+          "kind": "OBJECT",
+          "name": "T1",
+        },
+      }
+    `);
+  });
+});

gateway-js/src/executeQueryPlan.ts

@@ -11,6 +11,9 @@ import {
   executeSync,
   OperationTypeNode,
   FieldNode,
+  visit,
+  ASTNode,
+  VariableDefinitionNode,
 } from 'graphql';
 import { Trace, google } from '@apollo/usage-reporting-protobuf';
 import { GraphQLDataSource, GraphQLDataSourceRequestKind } from './datasources/types';
@@ -68,13 +71,33 @@ interface ExecutionContext {
   errors: GraphQLError[];
 }
 
-function makeIntrospectionQueryDocument(introspectionSelection: FieldNode): DocumentNode {
+function collectUsedVariables(node: ASTNode): Set<string> {
+  const usedVariables = new Set<string>();
+  visit(node, {
+    Variable: ({ name }) => {
+      usedVariables.add(name.value);
+    }
+  });
+  return usedVariables;
+}
+
+function makeIntrospectionQueryDocument(
+  introspectionSelection: FieldNode,
+  variableDefinitions?: readonly VariableDefinitionNode[],
+): DocumentNode {
+  const usedVariables = collectUsedVariables(introspectionSelection);
+  const usedVariableDefinitions = variableDefinitions?.filter((def) => usedVariables.has(def.variable.name.value));
+  assert(
+    usedVariables.size === (usedVariableDefinitions?.length ?? 0), 
+    () => `Should have found all used variables ${[...usedVariables]} in definitions ${JSON.stringify(variableDefinitions)}`,
+  );
   return {
     kind: Kind.DOCUMENT,
     definitions: [
       {
         kind: Kind.OPERATION_DEFINITION,
         operation: OperationTypeNode.QUERY,
+        variableDefinitions: usedVariableDefinitions,
         selectionSet: {
           kind: Kind.SELECTION_SET,
           selections: [ introspectionSelection ],
@@ -87,14 +110,21 @@ function makeIntrospectionQueryDocument(introspectionSelection: FieldNode): Docu
 function executeIntrospection(
   schema: GraphQLSchema,
   introspectionSelection: FieldNode,
+  variableDefinitions: ReadonlyArray<VariableDefinitionNode> | undefined,
+  variableValues: Record<string, any> | undefined,
 ): any {
-  const { data } = executeSync({
+  const { data, errors } = executeSync({
     schema,
-    document: makeIntrospectionQueryDocument(introspectionSelection),
+    document: makeIntrospectionQueryDocument(introspectionSelection, variableDefinitions),
     rootValue: {},
+    variableValues,
   });
+  assert(
+    !errors || errors.length === 0,
+    () => `Introspection query for ${JSON.stringify(introspectionSelection)} should not have failed but got ${JSON.stringify(errors)}`
+  );
   assert(data, () => `Introspection query for ${JSON.stringify(introspectionSelection)} should not have failed`);
-  return data[introspectionSelection.name.value];
+  return data[introspectionSelection.alias?.value ?? introspectionSelection.name.value];
 }
 
 export async function executeQueryPlan(
@@ -181,11 +211,17 @@ export async function executeQueryPlan(
         let data;
         try {
           let postProcessingErrors: GraphQLError[];
+          const variables = requestContext.request.variables;
           ({ data, errors: postProcessingErrors } = computeResponse({
             operation,
-            variables: requestContext.request.variables,
+            variables,
             input: unfilteredData,
-            introspectionHandling: (f) => executeIntrospection(operationContext.schema, f.expandAllFragments().toSelectionNode()),
+            introspectionHandling: (f) => executeIntrospection(
+              operationContext.schema,
+              f.expandAllFragments().toSelectionNode(),
+              operationContext.operation.variableDefinitions,
+              variables,
+            ),
           }));
 
           // If we have errors during the post-processing, we ignore them if any other errors have been thrown during