Add EmptyTypeAnnotation (#4724)

Added to Flow in facebook/flow#c603505583993aa953904005f91c350f4b65d6bd
Parser support added in babel/babylon#171.

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

@@ -167,6 +167,10 @@ export function MixedTypeAnnotation() {
   this.word("mixed");
 }
 
+export function EmptyTypeAnnotation() {
+  this.word("empty");
+}
+
 export function NullableTypeAnnotation(node: Object) {
   this.token("?");
   this.print(node.typeAnnotation, node);

packages/babel-traverse/src/path/inference/index.js

@@ -73,6 +73,8 @@ function _isBaseType(baseName: string, type?, soft?): boolean {
     return t.isAnyTypeAnnotation(type);
   } else if (baseName === "mixed") {
     return t.isMixedTypeAnnotation(type);
+  } else if (baseName === "empty") {
+    return t.isEmptyTypeAnnotation(type);
   } else if (baseName === "void") {
     return t.isVoidTypeAnnotation(type);
   } else {

packages/babel-types/README.md

@@ -755,6 +755,11 @@ See also `t.isMixedTypeAnnotation(node, opts)` and `t.assertMixedTypeAnnotation(
 
 Aliases: `Flow`, `FlowBaseAnnotation`
 
+### t.emptyTypeAnnotation()
+
+See also `t.isEmptyTypeAnnotation(node, opts)` and `t.assertEmptyTypeAnnotation(node, opts)`.
+
+Aliases: `Flow`, `FlowBaseAnnotation`
 
 ### t.newExpression(callee, arguments)
 

packages/babel-types/src/definitions/flow.js

@@ -167,6 +167,10 @@ defineType("MixedTypeAnnotation", {
   aliases: ["Flow", "FlowBaseAnnotation"]
 });
 
+defineType("EmptyTypeAnnotation", {
+  aliases: ["Flow", "FlowBaseAnnotation"]
+});
+
 defineType("NullableTypeAnnotation", {
   visitor: ["typeAnnotation"],
   aliases: ["Flow"],