Do not trigger use_build_context_synchronously on context.mounted

[kzrnm]

Description

Do not trigger use_build_context_synchronously on context.mounted.

Fixes dart-lang/sdk#59009 partially.

Fixed

class AsyncContextTestWidget extends StatelessWidget {
  const AsyncContextTestWidget({super.key});

  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: () async {
        await Future<void>.delayed(Duration.zero);

        // This line is marked as using context across async gaps
        if (!context.mounted) {
          return;
        }
      },
      child: const Text('Test'),
    );
  }
}

Not fixed

// This line triggers a warning too
final isMounted = context.mounted;

if (!isMounted) {
  return;
}

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[coveralls]

Coverage: 95.581% (+0.0005%) from 95.58% when pulling a06ce3c on kzrnm:fix/use_build_context_synchronously-/4007 into b3fb9e5 on dart-lang:main.

[kj415j45]

Looks good to me.

The not-fixed example you provided is against the lint.

Storing BuildContext for later usage can easily lead to difficult to diagnose crashes.

When a BuildContext is used, its mounted property must be checked after an asynchronous gap.

Consider the following code smell.

// Storing BuildContext.mounted
final isMounted = context.mounted;

// For developers unaware of this lint
// may insert some code here like below
await doSomething();

if (!isMounted) { // break the mounted guard
  return;
}

[srawlins]

I love it, thanks for the test.