Add support for leading vertical bar in union types

src/language/__tests__/schema-kitchen-sink.graphql

@@ -37,6 +37,8 @@ union Feed = Story | Article | Advert
 
 union AnnotatedUnion @onUnion = A | B
 
+union AnnotatedUnionTwo @onUnion = | A | B
+
 scalar CustomScalar
 
 scalar AnnotatedScalar @onScalar

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

@@ -457,6 +457,58 @@ type Hello {
     expect(printJson(doc)).to.equal(printJson(expected));
   });
 
+  it('Union with two types and leading vertical bar', () => {
+    const body = 'union Hello = | Wo | Rld';
+    const doc = parse(body);
+    const expected = {
+      kind: 'Document',
+      definitions: [
+        {
+          kind: 'UnionTypeDefinition',
+          name: nameNode('Hello', { start: 6, end: 11 }),
+          directives: [],
+          types: [
+            typeNode('Wo', { start: 16, end: 18 }),
+            typeNode('Rld', { start: 21, end: 24 }),
+          ],
+          loc: { start: 0, end: 24 },
+        }
+      ],
+      loc: { start: 0, end: 24 },
+    };
+    expect(printJson(doc)).to.equal(printJson(expected));
+  });
+
+  it('Union with no types and leading vertical bar', () => {
+    const body = 'union Hello = |';
+    expect(() => parse(body)).to.throw();
+  });
+
+  it('Union with types and ending vertical bar', () => {
+    const body = 'union Hello = Wo | Rld |';
+    expect(() => parse(body)).to.throw();
+  });
+
+  it('Union with types and double vertical bar at the beginning', () => {
+    const body = 'union Hello = || Wo | Rld';
+    expect(() => parse(body)).to.throw();
+  });
+
+  it('Union with types and double vertical bar in the middle', () => {
+    const body = 'union Hello = Wo || Rld';
+    expect(() => parse(body)).to.throw();
+  });
+
+  it('Union with types and double vertical bar at the end', () => {
+    const body = 'union Hello = | Wo | Rld ||';
+    expect(() => parse(body)).to.throw();
+  });
+
+  it('Union with types , leanding and ending vertical bar', () => {
+    const body = 'union Hello = | Wo | Rld |';
+    expect(() => parse(body)).to.throw();
+  });
+
   it('Union with two types', () => {
     const body = 'union Hello = Wo | Rld';
     const doc = parse(body);

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

@@ -83,6 +83,8 @@ union Feed = Story | Article | Advert
 
 union AnnotatedUnion @onUnion = A | B
 
+union AnnotatedUnionTwo @onUnion = A | B
+
 scalar CustomScalar
 
 scalar AnnotatedScalar @onScalar

src/language/parser.js

@@ -943,6 +943,9 @@ function parseUnionTypeDefinition(lexer: Lexer<*>): UnionTypeDefinitionNode {
  */
 function parseUnionMembers(lexer: Lexer<*>): Array<NamedTypeNode> {
   const members = [];
+  if (peek(lexer, TokenKind.PIPE)) {
+    skip(lexer, TokenKind.PIPE);
+  }
   do {
     members.push(parseNamedType(lexer));
   } while (skip(lexer, TokenKind.PIPE));