[dart:js_interop] Clear up wording about isA requiring non-generic type argument

Closes https://github.com/dart-lang/sdk/issues/56564

CoreLibraryReviewExempt: Doc-only change.
Change-Id: I0086a0778d53d850c8d746e0474d22382d5e451c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/381942
Commit-Queue: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>

pkg/_js_interop_checks/lib/src/transformations/shared_interop_transformer.dart

@@ -13,7 +13,7 @@ import 'package:front_end/src/api_prototype/codes.dart'
         templateJsInteropExportClassNotMarkedExportable,
         templateJsInteropExportInvalidInteropTypeArgument,
         templateJsInteropExportInvalidTypeArgument,
-        templateJsInteropIsAInvalidType,
+        templateJsInteropIsAInvalidTypeVariable,
         templateJsInteropIsAObjectLiteralType,
         templateJsInteropIsAPrimitiveExtensionType;
 import 'package:kernel/ast.dart';
@@ -149,8 +149,10 @@ class SharedInteropTransformer extends Transformer {
         // Generated tear-offs call the original method, so ignore that
         // invocation.
         if (!_inIsATearoff) {
+          assert(interopType is TypeParameterType);
           _diagnosticReporter.report(
-              templateJsInteropIsAInvalidType.withArguments(interopType),
+              templateJsInteropIsAInvalidTypeVariable
+                  .withArguments(interopType),
               invocation.fileOffset,
               invocation.name.text.length,
               invocation.location?.file);

pkg/front_end/lib/src/codes/cfe_codes_generated.dart

@@ -3849,34 +3849,35 @@ Message _withArgumentsJsInteropFunctionToJSRequiresStaticType(DartType _type) {
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<Message Function(DartType _type)>
-    templateJsInteropIsAInvalidType =
+    templateJsInteropIsAInvalidTypeVariable =
     const Template<Message Function(DartType _type)>(
-  "JsInteropIsAInvalidType",
+  "JsInteropIsAInvalidTypeVariable",
   problemMessageTemplate:
-      r"""Type argument '#type' needs to be an interop 'ExtensionType'.""",
+      r"""Type argument '#type' provided to 'isA' cannot be a type variable and must be an interop extension type that can be determined at compile-time.""",
   correctionMessageTemplate:
-      r"""Use a valid interop extension type as the type argument instead.""",
-  withArguments: _withArgumentsJsInteropIsAInvalidType,
+      r"""Use a valid interop extension type that can be determined at compile-time as the type argument instead.""",
+  withArguments: _withArgumentsJsInteropIsAInvalidTypeVariable,
 );
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
-const Code<Message Function(DartType _type)> codeJsInteropIsAInvalidType =
+const Code<Message Function(DartType _type)>
+    codeJsInteropIsAInvalidTypeVariable =
     const Code<Message Function(DartType _type)>(
-  "JsInteropIsAInvalidType",
+  "JsInteropIsAInvalidTypeVariable",
 );
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
-Message _withArgumentsJsInteropIsAInvalidType(DartType _type) {
+Message _withArgumentsJsInteropIsAInvalidTypeVariable(DartType _type) {
   TypeLabeler labeler = new TypeLabeler();
   List<Object> typeParts = labeler.labelType(_type);
   String type = typeParts.join();
   return new Message(
-    codeJsInteropIsAInvalidType,
+    codeJsInteropIsAInvalidTypeVariable,
     problemMessage:
-        """Type argument '${type}' needs to be an interop 'ExtensionType'.""" +
+        """Type argument '${type}' provided to 'isA' cannot be a type variable and must be an interop extension type that can be determined at compile-time.""" +
             labeler.originMessages,
     correctionMessage:
-        """Use a valid interop extension type as the type argument instead.""",
+        """Use a valid interop extension type that can be determined at compile-time as the type argument instead.""",
     arguments: {
       'type': _type,
     },

pkg/front_end/messages.status

@@ -647,8 +647,8 @@ JsInteropFunctionToJSTypeParameters/analyzerCode: Fail # Web compiler specific
 JsInteropFunctionToJSTypeParameters/example: Fail # Web compiler specific
 JsInteropInvalidStaticClassMemberName/analyzerCode: Fail
 JsInteropInvalidStaticClassMemberName/example: Fail
-JsInteropIsAInvalidType/analyzerCode: Fail # Web compiler specific
-JsInteropIsAInvalidType/example: Fail # Web compiler specific
+JsInteropIsAInvalidTypeVariable/analyzerCode: Fail # Web compiler specific
+JsInteropIsAInvalidTypeVariable/example: Fail # Web compiler specific
 JsInteropIsAObjectLiteralType/analyzerCode: Fail # Web compiler specific
 JsInteropIsAObjectLiteralType/example: Fail # Web compiler specific
 JsInteropIsAPrimitiveExtensionType/analyzerCode: Fail # Web compiler specific

pkg/front_end/messages.yaml

@@ -5701,9 +5701,9 @@ JsInteropExportNoExportableMembers:
   problemMessage: "Class '#name' has no exportable members in the class or the inheritance chain."
   correctionMessage: "Using `@JSExport`, annotate at least one instance member with a body or annotate a class that has such a member in the inheritance chain."
 
-JsInteropIsAInvalidType:
-  problemMessage: "Type argument '#type' needs to be an interop 'ExtensionType'."
-  correctionMessage: "Use a valid interop extension type as the type argument instead."
+JsInteropIsAInvalidTypeVariable:
+  problemMessage: "Type argument '#type' provided to 'isA' cannot be a type variable and must be an interop extension type that can be determined at compile-time."
+  correctionMessage: "Use a valid interop extension type that can be determined at compile-time as the type argument instead."
 
 JsInteropIsAObjectLiteralType:
   problemMessage: "Type argument '#type' has an object literal constructor. Because 'isA' uses the type's name or '@JS()' rename, this may result in an incorrect type check."

sdk/lib/js_interop/js_interop.dart

@@ -520,6 +520,11 @@ extension JSAnyUtilityExtension on JSAny? {
   /// Whether this <code>[JSAny]?</code> is an instance of the JavaScript type
   /// that is declared by [T].
   ///
+  /// Since the type-check this function emits is determined at compile-time,
+  /// [T] needs to be an interop extension type that can also be determined at
+  /// compile-time. In particular, `isA` can't be provided a generic type
+  /// variable as a type argument.
+  ///
   /// This method uses a combination of `null`, `typeof`, and `instanceof`
   /// checks in order to do this check. Use this instead of `is` checks.
   ///

tests/lib/js/static_interop_test/isa/static_test.dart

@@ -33,10 +33,10 @@ extension type CustomJSString(JSString _) implements JSString {}
 void test<T extends JSAny?, U extends NonLiteral>(JSAny? any) {
   any.isA<T>();
   //  ^
-  // [web] Type argument 'T' needs to be an interop 'ExtensionType'.
+  // [web] Type argument 'T' provided to 'isA' cannot be a type variable and must be an interop extension type that can be determined at compile-time.
   any.isA<U>();
   //  ^
-  // [web] Type argument 'U' needs to be an interop 'ExtensionType'.
+  // [web] Type argument 'U' provided to 'isA' cannot be a type variable and must be an interop extension type that can be determined at compile-time.
 
   final tearoff = 0.toJS.isA;
   //                     ^