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Published
20 hours ago •
dart-lang
dart-lang
Bug with dart2js
Hello team ! Not sure that it is still actual, but I found this bug on Dart 3.8.0 and Dart 3.10.3.
Consider the following Dart Code:
import 'dart:async';
void main() {
final processor = TestProcessor();
processor.test();
Timer(Duration(milliseconds: 100), () {
print('Expected: scheduleMicrotask called 1 time');
print('Actual: scheduleMicrotask called ${processor.microtaskCount} times');
if (processor.microtaskCount > 1) {
print('BUG!: Code after for+break is duplicated!');
}
});
}
class TestProcessor {
int microtaskCount = 0;
void test() {
print('test() called');
final items = <String>[];
for (final item in items) {
print('Processing item: $item');
break;
}
scheduleMicrotask(() {
microtaskCount++;
print('scheduleMicrotask callback executed');
});
print('test() completed');
}
}
Now the output from VM version:
dart run bug.dart
test() called
test() completed
scheduleMicrotask callback executed
Expected: scheduleMicrotask called 1 time
Actual: scheduleMicrotask called 1 times
Now the output from JS version (D8 environment):
./dart-sdk/bin/dart compile js -O0 bug.dart -o bug.js
./d8 --snapshot_blob=snapshot_blob.bin preamble.js bug.js
test() called
test() completed
test() completed
scheduleMicrotask callback executed
scheduleMicrotask callback executed
Expected: scheduleMicrotask called 1 time
Actual: scheduleMicrotask called 2 times
BUG!: Code after for+break is duplicated!
In browser (vscode internal):
<!DOCTYPE html>
<html>
<head><title>Test</title></head>
<body>
<script>
</script>
<script src="bug.js"></script>
</body>
</html>
___vscode_livepreview_injected_script:141 test() called
___vscode_livepreview_injected_script:141 test() completed
___vscode_livepreview_injected_script:141 test() completed
___vscode_livepreview_injected_script:141 scheduleMicrotask callback executed
___vscode_livepreview_injected_script:141 scheduleMicrotask callback executed
___vscode_livepreview_injected_script:141 Expected: scheduleMicrotask called 1 time
___vscode_livepreview_injected_script:141 Actual: scheduleMicrotask called 2 times
___vscode_livepreview_injected_script:141 BUG!: Code after for+break is duplicated!
And consider the generated JS code:
A.TestProcessor.prototype = {
test$0() {
A.print("test() called");
var t1 = B.JSArray_methods.get$iterator(A._setArrayType([], type$.JSArray_String));
$loop$0: {
if (t1.moveNext$0()) {
A.print("Processing item: " + t1.get$current());
break $loop$0;
}
A.scheduleMicrotask(new A.TestProcessor_test_closure(this));
A.print("test() completed");
}
A.scheduleMicrotask(new A.TestProcessor_test_closure(this));
A.print("test() completed");
}
};
The generated instructions are inside the $loop$0.
A.scheduleMicrotask(new A.TestProcessor_test_closure(this));
A.print("test() completed");
