introduce new Intersection type

Intersections of unions and interfaces can be considered to "implement" their unions and interface members.

A type with a field of type Intersection will satisfy an interface where the field defined in the interface is one of the member types of the intersection.

Alternative to #3527

docs-old/APIReference-GraphQL.md

@@ -66,6 +66,12 @@ _Type Definitions_
       A union type within GraphQL that defines a list of implementations.
     </a>
   </li>
+  <li>
+    <a href="../type/#graphqlintersectiontype">
+      <pre>class GraphQLIntersectionType</pre>
+      An intersection type within GraphQL that defines a list of constraining types.
+    </a>
+  </li>
   <li>
     <a href="../type/#graphqlenumtype">
       <pre>class GraphQLEnumType</pre>

docs-old/APIReference-TypeSystem.md

@@ -54,6 +54,12 @@ _Definitions_
       A union type within GraphQL that defines a list of implementations.
     </a>
   </li>
+  <li>
+    <a href="#graphqlintersectiontype">
+      <pre>class GraphQLIntersectionType</pre>
+      An intersection type within GraphQL that defines a list of constraining types.
+    </a>
+  </li>
   <li>
     <a href="#graphqlenumtype">
       <pre>class GraphQLEnumType</pre>

src/__testUtils__/kitchenSinkSDL.ts

@@ -79,6 +79,18 @@ extend union Feed = Photo | Video
 
 extend union Feed @onUnion
 
+intersection Resource = Feed & Node
+
+intersection AnnotatedIntersection @onIntersection = Feed & Node
+
+intersection AnnotatedIntersectionTwo @onIntersection = Feed & Node
+
+intersection UndefinedIntersection
+
+extend intersection Resource = Media & Accessible
+
+extend intersection Resource @onIntersection
+
 scalar CustomScalar
 
 scalar AnnotatedScalar @onScalar

src/index.ts

@@ -44,6 +44,7 @@ export {
   GraphQLObjectType,
   GraphQLInterfaceType,
   GraphQLUnionType,
+  GraphQLIntersectionType,
   GraphQLEnumType,
   GraphQLInputObjectType,
   GraphQLList,
@@ -90,6 +91,7 @@ export {
   isObjectType,
   isInterfaceType,
   isUnionType,
+  isIntersectionType,
   isEnumType,
   isInputObjectType,
   isListType,
@@ -115,6 +117,7 @@ export {
   assertObjectType,
   assertInterfaceType,
   assertUnionType,
+  assertIntersectionType,
   assertEnumType,
   assertInputObjectType,
   assertListType,
@@ -181,6 +184,8 @@ export type {
   GraphQLInputObjectTypeExtensions,
   GraphQLInterfaceTypeConfig,
   GraphQLInterfaceTypeExtensions,
+  GraphQLIntersectionTypeConfig,
+  GraphQLIntersectionTypeExtensions,
   GraphQLIsTypeOfFn,
   GraphQLObjectTypeConfig,
   GraphQLObjectTypeExtensions,

src/language/__tests__/predicates-test.ts

@@ -34,6 +34,7 @@ describe('AST node predicates', () => {
       'ObjectTypeDefinition',
       'InterfaceTypeDefinition',
       'UnionTypeDefinition',
+      'IntersectionTypeDefinition',
       'EnumTypeDefinition',
       'InputObjectTypeDefinition',
       'DirectiveDefinition',
@@ -42,6 +43,7 @@ describe('AST node predicates', () => {
       'ObjectTypeExtension',
       'InterfaceTypeExtension',
       'UnionTypeExtension',
+      'IntersectionTypeExtension',
       'EnumTypeExtension',
       'InputObjectTypeExtension',
     ]);
@@ -102,6 +104,7 @@ describe('AST node predicates', () => {
       'ObjectTypeDefinition',
       'InterfaceTypeDefinition',
       'UnionTypeDefinition',
+      'IntersectionTypeDefinition',
       'EnumTypeDefinition',
       'InputObjectTypeDefinition',
       'DirectiveDefinition',
@@ -114,6 +117,7 @@ describe('AST node predicates', () => {
       'ObjectTypeDefinition',
       'InterfaceTypeDefinition',
       'UnionTypeDefinition',
+      'IntersectionTypeDefinition',
       'EnumTypeDefinition',
       'InputObjectTypeDefinition',
     ]);
@@ -126,6 +130,7 @@ describe('AST node predicates', () => {
       'ObjectTypeExtension',
       'InterfaceTypeExtension',
       'UnionTypeExtension',
+      'IntersectionTypeExtension',
       'EnumTypeExtension',
       'InputObjectTypeExtension',
     ]);
@@ -137,6 +142,7 @@ describe('AST node predicates', () => {
       'ObjectTypeExtension',
       'InterfaceTypeExtension',
       'UnionTypeExtension',
+      'IntersectionTypeExtension',
       'EnumTypeExtension',
       'InputObjectTypeExtension',
     ]);

src/language/__tests__/schema-parser-test.ts

@@ -282,6 +282,11 @@ describe('Schema Parser', () => {
       locations: [{ line: 1, column: 19 }],
     });
 
+    expectSyntaxError('extend intersection Hello').to.deep.equal({
+      message: 'Syntax Error: Unexpected <EOF>.',
+      locations: [{ line: 1, column: 26 }],
+    });
+
     expectSyntaxError('extend enum Hello').to.deep.equal({
       message: 'Syntax Error: Unexpected <EOF>.',
       locations: [{ line: 1, column: 18 }],
@@ -961,6 +966,97 @@ describe('Schema Parser', () => {
     });
   });
 
+  it('Simple union', () => {
+    const doc = parse('intersection Hello = World');
+
+    expectJSON(doc).toDeepEqual({
+      kind: 'Document',
+      definitions: [
+        {
+          kind: 'IntersectionTypeDefinition',
+          name: nameNode('Hello', { start: 13, end: 18 }),
+          description: undefined,
+          directives: [],
+          types: [typeNode('World', { start: 21, end: 26 })],
+          loc: { start: 0, end: 26 },
+        },
+      ],
+      loc: { start: 0, end: 26 },
+    });
+  });
+
+  it('Intersection with two types', () => {
+    const doc = parse('intersection Hello = Wo & Rld');
+
+    expectJSON(doc).toDeepEqual({
+      kind: 'Document',
+      definitions: [
+        {
+          kind: 'IntersectionTypeDefinition',
+          name: nameNode('Hello', { start: 13, end: 18 }),
+          description: undefined,
+          directives: [],
+          types: [
+            typeNode('Wo', { start: 21, end: 23 }),
+            typeNode('Rld', { start: 26, end: 29 }),
+          ],
+          loc: { start: 0, end: 29 },
+        },
+      ],
+      loc: { start: 0, end: 29 },
+    });
+  });
+
+  it('Intersection with two types and leading ampersand', () => {
+    const doc = parse('intersection Hello = & Wo & Rld');
+
+    expectJSON(doc).toDeepEqual({
+      kind: 'Document',
+      definitions: [
+        {
+          kind: 'IntersectionTypeDefinition',
+          name: nameNode('Hello', { start: 13, end: 18 }),
+          description: undefined,
+          directives: [],
+          types: [
+            typeNode('Wo', { start: 23, end: 25 }),
+            typeNode('Rld', { start: 28, end: 31 }),
+          ],
+          loc: { start: 0, end: 31 },
+        },
+      ],
+      loc: { start: 0, end: 31 },
+    });
+  });
+
+  it('Intersection fails with no types', () => {
+    expectSyntaxError('intersection Hello = &').to.deep.equal({
+      message: 'Syntax Error: Expected Name, found <EOF>.',
+      locations: [{ line: 1, column: 23 }],
+    });
+  });
+
+  it('Intersection fails with leading double ampersand', () => {
+    expectSyntaxError('intersection Hello = && Wo & Rld').to.deep.equal({
+      message: 'Syntax Error: Expected Name, found "&".',
+      locations: [{ line: 1, column: 23 }],
+    });
+  });
+
+  it('Intersection fails with double ampersand', () => {
+    expectSyntaxError('intersection Hello = Wo && Rld').to.deep.equal({
+      message: 'Syntax Error: Expected Name, found "&".',
+      locations: [{ line: 1, column: 26 }],
+    });
+  });
+
+  it('Intersection fails with trailing ampersand', () => {
+    expectSyntaxError('intersection Hello = & Wo & Rld &').to.deep.equal({
+      message: 'Syntax Error: Expected Name, found <EOF>.',
+      locations: [{ line: 1, column: 34 }],
+    });
+  });
+
   it('Scalar', () => {
     const doc = parse('scalar Hello');
 

src/language/__tests__/schema-printer-test.ts

@@ -110,6 +110,18 @@ describe('Printer: SDL document', () => {
 
       extend union Feed @onUnion
 
+      intersection Resource = Feed & Node
+
+      intersection AnnotatedIntersection @onIntersection = Feed & Node
+
+      intersection AnnotatedIntersectionTwo @onIntersection = Feed & Node
+
+      intersection UndefinedIntersection
+
+      extend intersection Resource = Media & Accessible
+
+      extend intersection Resource @onIntersection
+      
       scalar CustomScalar
 
       scalar AnnotatedScalar @onScalar

src/language/ast.ts

@@ -169,6 +169,7 @@ export type ASTNode =
   | InputValueDefinitionNode
   | InterfaceTypeDefinitionNode
   | UnionTypeDefinitionNode
+  | IntersectionTypeDefinitionNode
   | EnumTypeDefinitionNode
   | EnumValueDefinitionNode
   | InputObjectTypeDefinitionNode
@@ -178,6 +179,7 @@ export type ASTNode =
   | ObjectTypeExtensionNode
   | InterfaceTypeExtensionNode
   | UnionTypeExtensionNode
+  | IntersectionTypeExtensionNode
   | EnumTypeExtensionNode
   | InputObjectTypeExtensionNode;
 
@@ -263,6 +265,7 @@ export const QueryDocumentKeys: {
     'fields',
   ],
   UnionTypeDefinition: ['description', 'name', 'directives', 'types'],
+  IntersectionTypeDefinition: ['description', 'name', 'directives', 'types'],
   EnumTypeDefinition: ['description', 'name', 'directives', 'values'],
   EnumValueDefinition: ['description', 'name', 'directives'],
   InputObjectTypeDefinition: ['description', 'name', 'directives', 'fields'],
@@ -275,6 +278,7 @@ export const QueryDocumentKeys: {
   ObjectTypeExtension: ['name', 'interfaces', 'directives', 'fields'],
   InterfaceTypeExtension: ['name', 'interfaces', 'directives', 'fields'],
   UnionTypeExtension: ['name', 'directives', 'types'],
+  IntersectionTypeExtension: ['name', 'directives', 'types'],
   EnumTypeExtension: ['name', 'directives', 'values'],
   InputObjectTypeExtension: ['name', 'directives', 'fields'],
 };
@@ -568,6 +572,7 @@ export type TypeDefinitionNode =
   | ObjectTypeDefinitionNode
   | InterfaceTypeDefinitionNode
   | UnionTypeDefinitionNode
+  | IntersectionTypeDefinitionNode
   | EnumTypeDefinitionNode
   | InputObjectTypeDefinitionNode;
 
@@ -628,6 +633,15 @@ export interface UnionTypeDefinitionNode {
   readonly types?: ReadonlyArray<NamedTypeNode>;
 }
 
+export interface IntersectionTypeDefinitionNode {
+  readonly kind: Kind.INTERSECTION_TYPE_DEFINITION;
+  readonly loc?: Location;
+  readonly description?: StringValueNode;
+  readonly name: NameNode;
+  readonly directives?: ReadonlyArray<ConstDirectiveNode>;
+  readonly types?: ReadonlyArray<NamedTypeNode>;
+}
+
 export interface EnumTypeDefinitionNode {
   readonly kind: Kind.ENUM_TYPE_DEFINITION;
   readonly loc?: Location;
@@ -684,6 +698,7 @@ export type TypeExtensionNode =
   | ObjectTypeExtensionNode
   | InterfaceTypeExtensionNode
   | UnionTypeExtensionNode
+  | IntersectionTypeExtensionNode
   | EnumTypeExtensionNode
   | InputObjectTypeExtensionNode;
 
@@ -720,6 +735,14 @@ export interface UnionTypeExtensionNode {
   readonly types?: ReadonlyArray<NamedTypeNode>;
 }
 
+export interface IntersectionTypeExtensionNode {
+  readonly kind: Kind.INTERSECTION_TYPE_EXTENSION;
+  readonly loc?: Location;
+  readonly name: NameNode;
+  readonly directives?: ReadonlyArray<ConstDirectiveNode>;
+  readonly types?: ReadonlyArray<NamedTypeNode>;
+}
+
 export interface EnumTypeExtensionNode {
   readonly kind: Kind.ENUM_TYPE_EXTENSION;
   readonly loc?: Location;

src/language/directiveLocation.ts

@@ -19,6 +19,7 @@ export enum DirectiveLocation {
   ARGUMENT_DEFINITION = 'ARGUMENT_DEFINITION',
   INTERFACE = 'INTERFACE',
   UNION = 'UNION',
+  INTERSECTION = 'INTERSECTION',
   ENUM = 'ENUM',
   ENUM_VALUE = 'ENUM_VALUE',
   INPUT_OBJECT = 'INPUT_OBJECT',

src/language/kinds.ts

@@ -49,6 +49,7 @@ export enum Kind {
   INPUT_VALUE_DEFINITION = 'InputValueDefinition',
   INTERFACE_TYPE_DEFINITION = 'InterfaceTypeDefinition',
   UNION_TYPE_DEFINITION = 'UnionTypeDefinition',
+  INTERSECTION_TYPE_DEFINITION = 'IntersectionTypeDefinition',
   ENUM_TYPE_DEFINITION = 'EnumTypeDefinition',
   ENUM_VALUE_DEFINITION = 'EnumValueDefinition',
   INPUT_OBJECT_TYPE_DEFINITION = 'InputObjectTypeDefinition',
@@ -64,6 +65,7 @@ export enum Kind {
   OBJECT_TYPE_EXTENSION = 'ObjectTypeExtension',
   INTERFACE_TYPE_EXTENSION = 'InterfaceTypeExtension',
   UNION_TYPE_EXTENSION = 'UnionTypeExtension',
+  INTERSECTION_TYPE_EXTENSION = 'IntersectionTypeExtension',
   ENUM_TYPE_EXTENSION = 'EnumTypeExtension',
   INPUT_OBJECT_TYPE_EXTENSION = 'InputObjectTypeExtension',
 }