Flow

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

@@ -2872,7 +2872,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
       // Either way, we're looking at a '<': tt.jsxTagStart or relational.
 
-      let typeParameters: N.TsTypeParameterDeclaration;
+      let typeParameters: ?N.TsTypeParameterDeclaration;
       state = state || this.state.clone();
 
       const arrow = this.tryParse(abort => {
@@ -2900,7 +2900,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         // This error is reported outside of the this.tryParse call so that
         // in case of <T>(x) => 2, we don't consider <T>(x) as a type assertion
         // because of this error.
-        this.reportReservedArrowTypeParam(typeParameters);
+        if (typeParameters) this.reportReservedArrowTypeParam(typeParameters);
         return arrow.node;
       }
 
@@ -2927,7 +2927,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       if (arrow.node) {
         /*:: invariant(arrow.failState) */
         this.state = arrow.failState;
-        this.reportReservedArrowTypeParam(typeParameters);
+        if (typeParameters) this.reportReservedArrowTypeParam(typeParameters);
         return arrow.node;
       }
 
@@ -2944,7 +2944,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       throw jsx?.error || arrow.error || typeCast?.error;
     }
 
-    reportReservedArrowTypeParam(node: N.TsTypeParameterDeclaration) {
+    reportReservedArrowTypeParam(node: any) {
       if (
         node.params.length === 1 &&
         !node.extra?.trailingComma &&