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[listen] Makes error context non-null #30

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[listen] Makes error context non-null #30

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4 changes: 4 additions & 0 deletions packages/listen/CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,3 +1,7 @@
## 1.0.0-beta.4

- `ErrorContext` is now a non-nullable parameter.

@gemini-code-assist gemini-code-assist Bot Jul 11, 2026

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medium

The changelog mentions that ErrorContext is now non-nullable, but it does not mention that it has been changed from an optional named parameter ({ErrorContext? context}) to a required positional parameter (ErrorContext context). Since this is a breaking change that requires updating call sites (removing the context: label), it would be highly beneficial to document this explicitly in the changelog.

Suggested change
- `ErrorContext` is now a non-nullable parameter.
- `ErrorContext` is now a required positional, non-nullable parameter.


## 1.0.0-beta.3

- Updates `ErrorCallback` to pass the raw error object and original `StackTrace`.
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9 changes: 4 additions & 5 deletions packages/listen/lib/src/listen.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -20,8 +20,7 @@ enum ErrorContext {
}

/// Signature of callbacks that are called when an error is reported by a listener or assertion.
typedef ErrorCallback =
void Function(Object error, StackTrace? stackTrace, {ErrorContext? context});
typedef ErrorCallback = void Function(Object error, StackTrace? stackTrace, ErrorContext context);

/// Signature of callbacks that are called when an object is created.
///
Expand Down Expand Up @@ -71,7 +70,7 @@ abstract class Listenable {
/// Error callback that is called when an error is thrown by a listener or assertion.
///
/// By default, errors are rethrown preserving their original [StackTrace].
static ErrorCallback onError = (Object error, StackTrace? stackTrace, {ErrorContext? context}) {
static ErrorCallback onError = (Object error, StackTrace? stackTrace, ErrorContext context) {
Error.throwWithStackTrace(error, stackTrace ?? StackTrace.current);
};

Expand Down Expand Up @@ -187,7 +186,7 @@ mixin class ChangeNotifier implements Listenable {
'can no longer be used.',
),
StackTrace.current,
context: ErrorContext.assertion,
ErrorContext.assertion,
);
}
return true;
Expand Down Expand Up @@ -437,7 +436,7 @@ mixin class ChangeNotifier implements Listenable {
try {
_listeners[i]?.call();
} catch (exception, stack) {
Listenable.onError(exception, stack, context: ErrorContext.listener);
Listenable.onError(exception, stack, ErrorContext.listener);
}
}

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2 changes: 1 addition & 1 deletion packages/listen/pubspec.yaml
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ name: listen
description: A package to notify state changes to interested listeners in pure Dart.
repository: https://github.com/flutter/core-packages/tree/main/packages/listen
issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+listen%22
version: 1.0.0-beta.3
version: 1.0.0-beta.4

environment:
sdk: ^3.10.0
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10 changes: 5 additions & 5 deletions packages/listen/test/listen_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,7 @@ void main() {
setUp(() {
lastError = null;
lastContext = null;
Listenable.onError = (Object error, StackTrace? stackTrace, {ErrorContext? context}) {
Listenable.onError = (Object error, StackTrace? stackTrace, ErrorContext context) {
lastError = error;
lastContext = context;
};
Expand Down Expand Up @@ -116,7 +116,7 @@ void main() {

final ErrorCallback original = Listenable.onError;
final List<Object> errors = [];
Listenable.onError = (Object error, StackTrace? stackTrace, {ErrorContext? context}) {
Listenable.onError = (Object error, StackTrace? stackTrace, ErrorContext context) {
errors.add(error);
};
addTearDown(() {
Expand Down Expand Up @@ -190,7 +190,7 @@ void main() {
test('Listenable.onError preserves runtime exception types', () {
final List<Object> errors = [];
final ErrorCallback original = Listenable.onError;
Listenable.onError = (Object error, StackTrace? stackTrace, {ErrorContext? context}) {
Listenable.onError = (Object error, StackTrace? stackTrace, ErrorContext context) {
errors.add(error);
};
addTearDown(() {
Expand All @@ -210,7 +210,7 @@ void main() {
test('Listenable.onError default implementation rethrows and preserves StackTrace', () {
final stack = StackTrace.fromString('test_stack_trace_marker');
try {
originalOnError(const FormatException('bad format'), stack);
originalOnError(const FormatException('bad format'), stack, ErrorContext.listener);
fail('Expected originalOnError to throw');
} catch (e, s) {
expect(e, isA<FormatException>());
Expand All @@ -221,7 +221,7 @@ void main() {
test('Listenable.onError reports correct ErrorContext across all failure types', () {
final List<ErrorContext?> contexts = [];
final ErrorCallback original = Listenable.onError;
Listenable.onError = (Object error, StackTrace? stackTrace, {ErrorContext? context}) {
Listenable.onError = (Object error, StackTrace? stackTrace, ErrorContext context) {
contexts.add(context);
};
addTearDown(() {
Expand Down
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