Add @oneOf support to introspection query

src/utilities/__tests__/buildClientSchema-test.ts

@@ -571,6 +571,21 @@ describe('Type System: build schema from introspection', () => {
     expect(cycleIntrospection(sdl)).to.equal(sdl);
   });
 
+  it('builds a schema with @oneOf directive', () => {
+    const sdl = dedent`
+      type Query {
+        someField(someArg: SomeInputObject): String
+      }
+
+      input SomeInputObject @oneOf {
+        someInputField1: String
+        someInputField2: String
+      }
+    `;
+
+    expect(cycleIntrospection(sdl)).to.equal(sdl);
+  });
+
   it('can use client schema for limited execution', () => {
     const schema = buildSchema(`
       scalar CustomScalar

src/utilities/__tests__/getIntrospectionQuery-test.ts

@@ -117,6 +117,14 @@ describe('getIntrospectionQuery', () => {
     );
   });
 
+  it('include "isOneOf" field on input objects', () => {
+    expectIntrospectionQuery().toNotMatch('isOneOf');
+
+    expectIntrospectionQuery({ inputObjectOneOf: true }).toMatch('isOneOf', 1);
+
+    expectIntrospectionQuery({ inputObjectOneOf: false }).toNotMatch('isOneOf');
+  });
+
   it('include deprecated input field and args', () => {
     expectIntrospectionQuery().toMatch('includeDeprecated: true', 2);
 

src/utilities/buildClientSchema.ts

@@ -311,6 +311,7 @@ export function buildClientSchema(
       name: inputObjectIntrospection.name,
       description: inputObjectIntrospection.description,
       fields: () => buildInputValueDefMap(inputObjectIntrospection.inputFields),
+      isOneOf: inputObjectIntrospection.isOneOf,
     });
   }
 

src/utilities/getIntrospectionQuery.ts

@@ -32,6 +32,10 @@ export interface IntrospectionOptions {
    * Default: false
    */
   inputValueDeprecation?: boolean;
+
+  // Whether target GraphQL server supports `@oneOf` input objects.
+  // Default: false
+  inputObjectOneOf?: boolean;
 }
 
 /**
@@ -45,6 +49,7 @@ export function getIntrospectionQuery(options?: IntrospectionOptions): string {
     directiveIsRepeatable: false,
     schemaDescription: false,
     inputValueDeprecation: false,
+    inputObjectOneOf: false,
     ...options,
   };
 
@@ -62,6 +67,7 @@ export function getIntrospectionQuery(options?: IntrospectionOptions): string {
   function inputDeprecation(str: string) {
     return optionsWithDefault.inputValueDeprecation ? str : '';
   }
+  const inputObjectOneOf = optionsWithDefault.inputObjectOneOf ? 'isOneOf' : '';
 
   return `
     query IntrospectionQuery {
@@ -90,6 +96,7 @@ export function getIntrospectionQuery(options?: IntrospectionOptions): string {
       name
       ${descriptions}
       ${specifiedByUrl}
+      ${inputObjectOneOf}
       fields(includeDeprecated: true) {
         name
         ${descriptions}
@@ -223,6 +230,7 @@ export interface IntrospectionObjectType {
   readonly interfaces: ReadonlyArray<
     IntrospectionNamedTypeRef<IntrospectionInterfaceType>
   >;
+  readonly isOneOf: boolean;
 }
 
 export interface IntrospectionInterfaceType {
@@ -259,6 +267,7 @@ export interface IntrospectionInputObjectType {
   readonly name: string;
   readonly description?: Maybe<string>;
   readonly inputFields: ReadonlyArray<IntrospectionInputValue>;
+  readonly isOneOf: boolean;
 }
 
 export interface IntrospectionListTypeRef<

src/utilities/introspectionFromSchema.ts

@@ -30,6 +30,7 @@ export function introspectionFromSchema(
     directiveIsRepeatable: true,
     schemaDescription: true,
     inputValueDeprecation: true,
+    inputObjectOneOf: true,
     ...options,
   };