[dart2wasm] Fix int.parse(<str>) for when <str> is a JSString

The `int.parse()` function would - if radix is provided and not 10 - use
functions that `unsafeCast<StringBase>()`.

=> The string can be a JSString.

Issue https://github.com/dart-lang/sdk/issues/54800

CoreLibraryReviewExempt: Adding test that should pass on all backends.
Change-Id: Ie6efa5bc545cadce5ea946e2c1d732b2cf94e306
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/350303
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>

sdk/lib/_internal/wasm/lib/int_patch.dart

@@ -4,6 +4,7 @@
 
 import "dart:_internal" show has63BitSmis, patch, unsafeCast;
 import "dart:_string" show StringBase;
+import "dart:_js_types" show JSStringImpl;
 
 import "dart:typed_data" show Int64List;
 
@@ -51,11 +52,11 @@ class int {
       throw RangeError("Radix $radix not in range 2..36");
     }
     // Split here so improve odds of parse being inlined and the checks omitted.
-    return _parse(unsafeCast<StringBase>(source), radix, onError) as int;
+    return _parse(source, radix, onError) as int;
   }
 
   static int? _parse(
-      StringBase source, int? radix, int? Function(String)? onError) {
+      String source, int? radix, int? Function(String)? onError) {
     int end = source.lastNonWhitespace() + 1;
     if (end == 0) {
       return _handleFormatError(onError, source, source.length, radix, null);
@@ -94,7 +95,6 @@ class int {
 
   @patch
   static int? tryParse(String source, {int? radix}) {
-    if (source == null) throw ArgumentError("The source must not be null");
     if (source.isEmpty) return null;
     if (radix == null || radix == 10) {
       // Try parsing immediately, without trimming whitespace.
@@ -103,7 +103,7 @@ class int {
     } else if (radix < 2 || radix > 36) {
       throw RangeError("Radix $radix not in range 2..36");
     }
-    return _parse(unsafeCast<StringBase>(source), radix, _kNull);
+    return _parse(source, radix, _kNull);
   }
 
   static Null _kNull(_) => null;

sdk/lib/_internal/wasm/lib/string_patch.dart

@@ -4,6 +4,7 @@
 
 import "dart:_internal" show patch;
 import "dart:_string";
+import "dart:_js_types" show JSStringImpl;
 
 @patch
 class String {
@@ -50,3 +51,17 @@ class String {
   external const factory String.fromEnvironment(String name,
       {String defaultValue = ""});
 }
+
+extension _StringExt on String {
+  int firstNonWhitespace() {
+    final value = this;
+    if (value is StringBase) return value.firstNonWhitespace();
+    return (value as JSStringImpl).firstNonWhitespace();
+  }
+
+  int lastNonWhitespace() {
+    final value = this;
+    if (value is StringBase) return value.lastNonWhitespace();
+    return (value as JSStringImpl).lastNonWhitespace();
+  }
+}

tests/corelib/regress_54800_test.dart

@@ -0,0 +1,11 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:expect/expect.dart';
+
+void main() {
+  final match = RegExp(r' ([0-9]+) ').allMatches('  1234   ').single;
+  print(match[1]!.runtimeType);
+  Expect.equals(0x1234, int.parse(match[1]!, radix: 16));
+}