[dart2wasm] Introduce a --minify flag to dart2wasm that uses "minified:Class<cid>" for class names

The `minified:...` encoding of class names mirrors the one used by
dart2js. So the added test will work in both modes.

This reduces optimized dart2wasm output

* hello world by 20%
* flute complex by 8.5%

Change-Id: I080de40919ee3f25f0f0d8c9b82aa662f7e734aa
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/347741
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>

pkg/dart2wasm/lib/dart2wasm.dart

@@ -27,6 +27,8 @@ final List<Option> options = [
       defaultsTo: _d.translatorOptions.inlining),
   Flag("name-section", (o, value) => o.translatorOptions.nameSection = value,
       defaultsTo: _d.translatorOptions.nameSection),
+  Flag("minify", (o, value) => o.translatorOptions.minify = value,
+      defaultsTo: _d.translatorOptions.minify),
   Flag("polymorphic-specialization",
       (o, value) => o.translatorOptions.polymorphicSpecialization = value,
       defaultsTo: _d.translatorOptions.polymorphicSpecialization),

pkg/dart2wasm/lib/translator.dart

@@ -38,6 +38,7 @@ class TranslatorOptions {
   bool polymorphicSpecialization = false;
   bool printKernel = false;
   bool printWasm = false;
+  bool minify = false;
   bool verifyTypeChecks = false;
   int inliningLimit = 0;
   int? sharedMemoryMaxPages;

pkg/dart2wasm/lib/types.dart

@@ -290,13 +290,16 @@ class Types {
     final arrayOfStringType = InterfaceType(
         translator.wasmArrayClass, Nullability.nonNullable, [stringType]);
 
-    final arrayOfStrings = translator.constants.makeArrayOf(
-        stringType, [for (final name in typeNames) StringConstant(name)]);
-
     final typeNamesType =
         translator.translateStorageType(arrayOfStringType).unpacked;
-    translator.constants
-        .instantiateConstant(null, b, arrayOfStrings, typeNamesType);
+    if (translator.options.minify) {
+      b.ref_null((typeNamesType as w.RefType).heapType);
+    } else {
+      final arrayOfStrings = translator.constants.makeArrayOf(
+          stringType, [for (final name in typeNames) StringConstant(name)]);
+      translator.constants
+          .instantiateConstant(null, b, arrayOfStrings, typeNamesType);
+    }
     return typeNamesType;
   }
 

sdk/lib/_internal/wasm/lib/type.dart

@@ -303,7 +303,7 @@ class _InterfaceType extends _Type {
   @override
   String toString() {
     StringBuffer s = StringBuffer();
-    s.write(_getTypeNames()[classId]);
+    s.write(_getTypeNames()?[classId] ?? 'minified:Class${classId}');
     if (typeArguments.isNotEmpty) {
       s.write("<");
       for (int i = 0; i < typeArguments.length; i++) {
@@ -602,7 +602,7 @@ class _RecordType extends _Type {
 
 external WasmArray<WasmArray<WasmI32>> _getTypeRulesSupers();
 external WasmArray<WasmArray<WasmArray<_Type>>> _getTypeRulesSubstitutions();
-external WasmArray<String> _getTypeNames();
+external WasmArray<String>? _getTypeNames();
 
 /// Type parameter environment used while comparing function types.
 ///

tests/web/wasm_js_shared/minify_test.dart

@@ -0,0 +1,33 @@
+// 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.
+
+// dart2jsOptions=--minify
+// dart2wasmOptions=--minify
+
+import 'package:expect/expect.dart';
+import 'package:expect/config.dart';
+
+void main() {
+  // This test is specific to testing dart2wasm & dart2js.
+  if (!isDart2jsConfiguration && !isDart2WasmConfiguration) return;
+
+  final obj = int.parse('1') == 1 ? Foo<Bar>() : Foo<Baz>();
+  final runtimeType = obj.runtimeType.toString();
+  final match = RegExp(r'^minified:[A-Za-z0-9]+<minified:[A-Za-z0-9]+>$')
+      .matchAsPrefix(runtimeType);
+  Expect.isNotNull(
+      match,
+      'Foo<Bar>().runtimeType should have format '
+      'minified:XXX<minified:YYY> but was $runtimeType');
+  Expect.isTrue(obj.isT(Bar()));
+  Expect.isTrue(!obj.isT(Baz()));
+}
+
+class Foo<T> {
+  bool isT(Object obj) => obj is T;
+}
+
+class Bar {}
+
+class Baz {}