Add support for flow's SymbolTypeAnnotation (#11077)

packages/babel-generator/src/generators/flow.js

@@ -596,6 +596,10 @@ export function QualifiedTypeIdentifier(node: Object) {
   this.print(node.id, node);
 }
 
+export function SymbolTypeAnnotation() {
+  this.word("symbol");
+}
+
 function orSeparator() {
   this.space();
   this.token("|");

packages/babel-generator/test/fixtures/flow/declare-statements/input.js

@@ -23,3 +23,4 @@ declare opaque type Foo<T>: Bar<T>;
 declare opaque type ID;
 declare opaque type num: number;
 declare opaque type NumArray;
+declare var sym: symbol;

packages/babel-generator/test/fixtures/flow/declare-statements/output.js

@@ -41,4 +41,5 @@ declare module.exports: {
 declare opaque type Foo<T>: Bar<T>;
 declare opaque type ID;
 declare opaque type num: number;
-declare opaque type NumArray;
+declare opaque type NumArray;
+declare var sym: symbol;

packages/babel-generator/test/fixtures/flow/type-annotations/input.js

@@ -128,3 +128,4 @@ var a34: {| id<T>(x: T): T; |};
 function foo27(numVal: number = 2) {}
 function foo28(numVal?: number = 2) {}
 export type * from "foo";
+const foo29: symbol = Symbol();

packages/babel-generator/test/fixtures/flow/type-annotations/output.js

@@ -293,4 +293,5 @@ function foo27(numVal: number = 2) {}
 
 function foo28(numVal?: number = 2) {}
 
-export type * from "foo";
+export type * from "foo";
+const foo29: symbol = Symbol();