Steps to Reproduce
Note: This is a compilation error with Flutter 3.38's dart2wasm compiler, not a runtime HTML rendering issue.
- Update to Flutter 3.38.0 or later
- Attempt to build a web app using WASM:
flutter build web --release --wasm
- The build fails during dart2wasm compilation
HTML
N/A - This is a build-time compilation error
`HtmlWidget` configuration
N/A - This is a build-time compilation error
Testing environment
[✓] Flutter (Channel stable, 3.38.2, on macOS 15.4.0 darwin-arm64)
• Flutter version 3.38.2 on channel stable
• Dart version 3.10.0
• Package: flutter_widget_from_html_core 0.17.0
Building with: flutter build web --release --wasm
Expected results
The app should compile successfully with WASM as it did in Flutter 3.35 and earlier versions.
Actual results
Build fails with compilation error:
Target dart2wasm failed: ProcessException: Process exited abnormally with exit code 255:
Exception in SwitchStatement at
file:///.../.pub-cache/hosted/pub.dev/flutter_widget_from_html_core-0.17.0/lib/src/data/build_op.dart:172:17
Unhandled exception:
type 'NullConstant' is not a subtype of type 'IntConstant' in type cast
#0 new SwitchInfo (package:dart2wasm/code_generator.dart:4543)
#1 AstCodeGenerator.visitSwitchStatement (package:dart2wasm/code_generator.dart:1368)
Root cause: The switch statement at build_op.dart:172-183 mixes null and integer case values:
switch (children?.length) {
case null: // NullConstant
return placeholder;
case 0: // IntConstant
return widget0;
case 1: // IntConstant
return children?.first ?? widget0;
default:
throw UnsupportedError(...);
}The dart2wasm compiler in Flutter 3.38+ is stricter and no longer allows mixing NullConstant and IntConstant types in the same switch statement.
Proposed fix: Refactor to use if-else logic instead of a switch statement.
Steps to Reproduce
Note: This is a compilation error with Flutter 3.38's dart2wasm compiler, not a runtime HTML rendering issue.
flutter build web --release --wasmHTML
`HtmlWidget` configuration
Testing environment
Expected results
The app should compile successfully with WASM as it did in Flutter 3.35 and earlier versions.
Actual results
Build fails with compilation error:
Root cause: The switch statement at
build_op.dart:172-183mixesnulland integer case values:The dart2wasm compiler in Flutter 3.38+ is stricter and no longer allows mixing
NullConstantandIntConstanttypes in the same switch statement.Proposed fix: Refactor to use if-else logic instead of a switch statement.