[TS] Allow context type annotation on getters/setters (#9641)

* Allow context type annotation on getters/setters

* Extract getAccessorsExpectedParamCount

packages/babel-parser/src/parser/expression.js

@@ -1564,10 +1564,16 @@ export default class ExpressionParser extends LValParser {
     );
   }
 
+  getGetterSetterExpectedParamCount(
+    method: N.ObjectMethod | N.ClassMethod,
+  ): number {
+    return method.kind === "get" ? 0 : 1;
+  }
+
   // get methods aren't allowed to have any parameters
   // set methods must have exactly 1 parameter which is not a rest parameter
   checkGetterSetterParams(method: N.ObjectMethod | N.ClassMethod): void {
-    const paramCount = method.kind === "get" ? 0 : 1;
+    const paramCount = this.getGetterSetterExpectedParamCount(method);
     const start = method.start;
     if (method.params.length !== paramCount) {
       if (method.kind === "get") {
@@ -1577,7 +1583,10 @@ export default class ExpressionParser extends LValParser {
       }
     }
 
-    if (method.kind === "set" && method.params[0].type === "RestElement") {
+    if (
+      method.kind === "set" &&
+      method.params[method.params.length - 1].type === "RestElement"
+    ) {
       this.raise(
         start,
         "setter function argument must not be a rest parameter",

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

@@ -2344,4 +2344,17 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       if (typeArguments) node.typeParameters = typeArguments;
       return super.jsxParseOpeningElementAfterName(node);
     }
+
+    getGetterSetterExpectedParamCount(
+      method: N.ObjectMethod | N.ClassMethod,
+    ): number {
+      const baseCount = super.getGetterSetterExpectedParamCount(method);
+      const firstParam = method.params[0];
+      const hasContextParam =
+        firstParam &&
+        firstParam.type === "Identifier" &&
+        firstParam.name === "this";
+
+      return hasContextParam ? baseCount + 1 : baseCount;
+    }
   };