[TS] Disallow type casts in arrow parameters (#9612)

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

@@ -2268,8 +2268,18 @@ export default (superClass: Class<Parser>): Class<Parser> =>
     ): $ReadOnlyArray<N.Pattern> {
       for (let i = 0; i < exprList.length; i++) {
         const expr = exprList[i];
-        if (expr && expr.type === "TSTypeCastExpression") {
+        if (!expr) continue;
+        switch (expr.type) {
+          case "TSTypeCastExpression":
             exprList[i] = this.typeCastToParameter(expr);
+            break;
+          case "TSAsExpression":
+          case "TSTypeAssertion":
+            this.raise(
+              expr.start,
+              "Unexpected type cast in parameter position.",
+            );
+            break;
         }
       }
       return super.toAssignableList(exprList, isBinding, contextDescription);

packages/babel-parser/test/fixtures/typescript/cast/arrow-async-parameter-as/input.js

@@ -0,0 +1 @@
+async (a as T) => {};

packages/babel-parser/test/fixtures/typescript/cast/arrow-async-parameter-as/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Unexpected type cast in parameter position. (1:7)"
+}

packages/babel-parser/test/fixtures/typescript/cast/arrow-async-parameter-assertion/input.js

@@ -0,0 +1 @@
+async (<T> a) => {};

packages/babel-parser/test/fixtures/typescript/cast/arrow-async-parameter-assertion/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Unexpected type cast in parameter position. (1:7)"
+}

packages/babel-parser/test/fixtures/typescript/cast/arrow-parameter-as/input.js

@@ -0,0 +1 @@
+(a as T) => {};

packages/babel-parser/test/fixtures/typescript/cast/arrow-parameter-as/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Unexpected type cast in parameter position. (1:1)"
+}

packages/babel-parser/test/fixtures/typescript/cast/arrow-parameter-assertion/input.js

@@ -0,0 +1 @@
+(<T> a) => {};

packages/babel-parser/test/fixtures/typescript/cast/arrow-parameter-assertion/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Unexpected type cast in parameter position. (1:1)"
+}