Don't use sync*, as it is unimplemented in dart2wasm.

third_party/web_locale_keymap/lib/web_locale_keymap/key_mappings.g.dart

@@ -5,15 +5,15 @@
 
 // DO NOT EDIT -- DO NOT EDIT -- DO NOT EDIT
 //
-// This file is auto generated by flutter/engine:flutter/tools/gen_web_keyboard_layouts based on
-// https://github.com/microsoft/vscode/tree/ab7ccc9e872dfcdfc429f8f2815109ec0ca926e3/src/vs/workbench/services/keybinding/browser/keyboardLayouts
+// This file is auto generated by flutter/engine:flutter/tools/gen_web_keyboard_keymap based on
+// https://github.com/microsoft/vscode/tree/422b581e3802e30cfb780c21d9cc1a2cd0c9f0aa/src/vs/workbench/services/keybinding/browser/keyboardLayouts
 //
 // Edit the following files instead:
 //
 //  - Script: lib/main.dart
 //  - Templates: data/*.tmpl
 //
-// See flutter/engine:flutter/tools/gen_web_keyboard_layouts/README.md for more information.
+// See flutter/engine:flutter/tools/gen_web_locale_keymap/README.md for more information.
 
 /// Used in the final mapping indicating the logical key should be derived from
 /// KeyboardEvent.keyCode.
@@ -100,16 +100,17 @@ bool isLetter(int charCode) {
 ///
 /// This greatly reduces the entries needed in the final mapping.
 int? heuristicMapper(String code, String key) {
-  // Digit code: return the digit.
+  // Digit code: return the digit by event code.
   if (code.startsWith('Digit')) {
     assert(code.length == 6);
     return code.codeUnitAt(5); // The character immediately after 'Digit'
   }
   final int charCode = key.codeUnitAt(0);
+  // Non-ascii: return the goal (i.e. US mapping by event code).
   if (key.length > 1 || !_isAscii(charCode)) {
     return kLayoutGoals[code]?.codeUnitAt(0);
   }
-  // Letter key: return the letter.
+  // Letter key: return the event key letter.
   if (isLetter(charCode)) {
     return key.toLowerCase().codeUnitAt(0);
   }
@@ -167,22 +168,20 @@ class _StringStream {
 
 Map<String, int> _unmarshallCodeMap(_StringStream stream) {
   final int entryNum = stream.readIntAsVerbatim();
-  return Map<String, int>.fromEntries((() sync* {
-    for (int entryIndex = 0; entryIndex < entryNum; entryIndex += 1) {
-      yield MapEntry<String, int>(stream.readEventKey(), stream.readIntAsChar());
-    }
-  })());
+  return <String, int>{
+    for (int i = 0; i < entryNum; i++)
+      stream.readEventKey(): stream.readIntAsChar(),
+  };
 }
 
 /// Decode a key mapping data out of the string.
 Map<String, Map<String, int>> unmarshallMappingData(String compressed) {
   final _StringStream stream = _StringStream(compressed);
   final int eventCodeNum = stream.readIntAsVerbatim();
-  return Map<String, Map<String, int>>.fromEntries((() sync* {
-    for (int eventCodeIndex = 0; eventCodeIndex < eventCodeNum; eventCodeIndex += 1) {
-      yield MapEntry<String, Map<String, int>>(stream.readEventCode(), _unmarshallCodeMap(stream));
-    }
-  })());
+  return <String, Map<String, int>>{
+    for (int i = 0; i < eventCodeNum; i++)
+      stream.readEventCode() : _unmarshallCodeMap(stream),
+  };
 }
 
 /// Data for [LocaleKeymap] on Windows.

third_party/web_locale_keymap/test/test_cases.g.dart

@@ -5,15 +5,15 @@
 
 // DO NOT EDIT -- DO NOT EDIT -- DO NOT EDIT
 //
-// This file is auto generated by flutter/engine:flutter/tools/gen_web_keyboard_layouts based on
+// This file is auto generated by flutter/engine:flutter/tools/gen_web_keyboard_keymap based on
 // https://github.com/microsoft/vscode/tree/@@@COMMIT_ID@@@/src/vs/workbench/services/keybinding/browser/keyboardLayouts
 //
 // Edit the following files instead:
 //
 //  - Script: lib/main.dart
 //  - Templates: data/*.tmpl
 //
-// See flutter/engine:flutter/tools/gen_web_keyboard_layouts/README.md for more information.
+// See flutter/engine:flutter/tools/gen_web_keyboard_keymap/README.md for more information.
 
 import 'package:test/test.dart';
 import 'package:web_locale_keymap/web_locale_keymap.dart';

tools/gen_web_locale_keymap/bin/gen_web_locale_keymap.dart

@@ -5,10 +5,10 @@
 import 'dart:io';
 
 import 'package:args/args.dart';
-import 'package:gen_web_keyboard_layouts/benchmark_planner.dart';
-import 'package:gen_web_keyboard_layouts/common.dart';
-import 'package:gen_web_keyboard_layouts/github.dart';
-import 'package:gen_web_keyboard_layouts/layout_types.dart';
+import 'package:gen_web_keyboard_keymap/benchmark_planner.dart';
+import 'package:gen_web_keyboard_keymap/common.dart';
+import 'package:gen_web_keyboard_keymap/github.dart';
+import 'package:gen_web_keyboard_keymap/layout_types.dart';
 import 'package:path/path.dart' as path;
 
 const String kEnvGithubToken = 'GITHUB_TOKEN';

tools/gen_web_locale_keymap/data/key_mappings.dart.tmpl

@@ -5,15 +5,15 @@
 
 // DO NOT EDIT -- DO NOT EDIT -- DO NOT EDIT
 //
-// This file is auto generated by flutter/engine:flutter/tools/gen_web_keyboard_layouts based on
+// This file is auto generated by flutter/engine:flutter/tools/gen_web_keyboard_keymap based on
 // @@@COMMIT_URL@@@
 //
 // Edit the following files instead:
 //
 //  - Script: lib/main.dart
 //  - Templates: data/*.tmpl
 //
-// See flutter/engine:flutter/tools/gen_web_keyboard_layouts/README.md for more information.
+// See flutter/engine:flutter/tools/gen_web_locale_keymap/README.md for more information.
 @@@COMMON@@@
 
 /// Data for [LocaleKeymap] on Windows.

tools/gen_web_locale_keymap/data/test_cases.dart.tmpl

@@ -5,15 +5,15 @@
 
 // DO NOT EDIT -- DO NOT EDIT -- DO NOT EDIT
 //
-// This file is auto generated by flutter/engine:flutter/tools/gen_web_keyboard_layouts based on
+// This file is auto generated by flutter/engine:flutter/tools/gen_web_keyboard_keymap based on
 // https://github.com/microsoft/vscode/tree/@@@COMMIT_ID@@@/src/vs/workbench/services/keybinding/browser/keyboardLayouts
 //
 // Edit the following files instead:
 //
 //  - Script: lib/main.dart
 //  - Templates: data/*.tmpl
 //
-// See flutter/engine:flutter/tools/gen_web_keyboard_layouts/README.md for more information.
+// See flutter/engine:flutter/tools/gen_web_keyboard_keymap/README.md for more information.
 
 import 'package:test/test.dart';
 import 'package:web_locale_keymap/web_locale_keymap.dart';

tools/gen_web_locale_keymap/lib/common.dart

@@ -159,22 +159,20 @@ class _StringStream {
 
 Map<String, int> _unmarshallCodeMap(_StringStream stream) {
   final int entryNum = stream.readIntAsVerbatim();
-  return Map<String, int>.fromEntries((() sync* {
-    for (int entryIndex = 0; entryIndex < entryNum; entryIndex += 1) {
-      yield MapEntry<String, int>(stream.readEventKey(), stream.readIntAsChar());
-    }
-  })());
+  return <String, int>{
+    for (int i = 0; i < entryNum; i++)
+      stream.readEventKey(): stream.readIntAsChar(),
+  };
 }
 
 /// Decode a key mapping data out of the string.
 Map<String, Map<String, int>> unmarshallMappingData(String compressed) {
   final _StringStream stream = _StringStream(compressed);
   final int eventCodeNum = stream.readIntAsVerbatim();
-  return Map<String, Map<String, int>>.fromEntries((() sync* {
-    for (int eventCodeIndex = 0; eventCodeIndex < eventCodeNum; eventCodeIndex += 1) {
-      yield MapEntry<String, Map<String, int>>(stream.readEventCode(), _unmarshallCodeMap(stream));
-    }
-  })());
+  return <String, Map<String, int>>{
+    for (int i = 0; i < eventCodeNum; i++)
+      stream.readEventCode() : _unmarshallCodeMap(stream),
+  };
 }
 
 /*@@@ SHARED SEGMENT END @@@*/

tools/gen_web_locale_keymap/pubspec.yaml

@@ -1,4 +1,4 @@
-name: gen_web_keyboard_layouts
+name: gen_web_keyboard_keymap
 description: Generates keyboard layouts for Web from external sources.
 
 environment: