Typescript - Tuple elements can be optional (#8720)

packages/babel-parser/src/plugins/typescript.js

@@ -503,13 +503,23 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       const node: N.TsTupleType = this.startNode();
       node.elementTypes = this.tsParseBracketedList(
         "TupleElementTypes",
-        this.tsParseType.bind(this),
+        this.tsParseTupleElementType.bind(this),
         /* bracket */ true,
         /* skipFirstToken */ false,
       );
       return this.finishNode(node, "TSTupleType");
     }
 
+    tsParseTupleElementType(): N.TsType {
+      const type = this.tsParseType();
+      if (this.eat(tt.question)) {
+        const optionalTypeNode: N.TsOptionalType = this.startNodeAtNode(type);
+        optionalTypeNode.typeAnnotation = type;
+        return this.finishNode(optionalTypeNode, "TSOptionalType");
+      }
+      return type;
+    }
+
     tsParseParenthesizedType(): N.TsParenthesizedType {
       const node = this.startNode();
       this.expect(tt.parenL);

packages/babel-parser/src/types.js

@@ -1104,6 +1104,7 @@ export type TsType =
   | TsTypeLiteral
   | TsArrayType
   | TsTupleType
+  | TsOptionalType
   | TsUnionOrIntersectionType
   | TsConditionalType
   | TsInferType
@@ -1184,6 +1185,11 @@ export type TsTupleType = TsTypeBase & {
   elementTypes: $ReadOnlyArray<TsType>,
 };
 
+export type TsOptionalType = TsTypeBase & {
+  type: "TSOptionalType",
+  typeAnnotation: TsType,
+};
+
 export type TsUnionOrIntersectionType = TsUnionType | TsIntersectionType;
 
 export type TsUnionOrIntersectionTypeBase = TsTypeBase & {