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Merged
auto-submit merged 1 commit into from
Sep 12, 2025
Merged

[CP-beta][shell] Fix engineId not being set after hot restart #175254

auto-submit merged 1 commit into from
Sep 12, 2025

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@flutteractionsbot flutteractionsbot commented Sep 12, 2025 •
edited by HosseinYousefi
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This pull request is created by automatic cherry pick workflow
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

Issue Link:

What is the link to the issue this cherry-pick is addressing?

#173474

Changelog Description:

Explain this cherry pick in one line that is accessible to most Flutter developers. See best practices for examples

PlatformDispatchers.instance.engineId returns null after hot restart

Impact Description:

What is the impact (ex. visual jank on Samsung phones, app crash, cannot ship an iOS app)? Does it impact development (ex. flutter doctor crashes when Android Studio is installed), or the shipping production app (the app crashes on launch)

It affects anyone who uses engineId while in development (since it happens after hot-restart).

Workaround:

Is there a workaround for this issue?

Not doing any hot-restarting while development which is not ideal.

Risk:

What is the risk level of this cherry-pick?

  • Low
  • Medium
  • High

Test Coverage:

Are you confident that your fix is well-tested by automated tests?

  • Yes
  • No

Validation Steps:

What are the steps to validate that this fix works?

Running this app and hot restarting no longer prints null:

class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  void initState() {
    super.initState();
    print('engineId: ${PlatformDispatcher.instance.engineId}');
  }
  // ...
}

@knopp
[shell] Fix engineId not being set after hot restart (flutter#174451)
c409735 
Fixes flutter#173474

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@flutteractionsbot flutteractionsbot added the cp: review Cherry-picks in the review queue label Sep 12, 2025
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flutteractionsbot commented Sep 12, 2025

@HosseinYousefi please fill out the PR description above, afterwards the release team will review this request.

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This pull request was opened from and to a release candidate branch. This should only be done as part of the official Flutter release process. If you are attempting to make a regular contribution to the Flutter project, please close this PR and follow the instructions at Tree Hygiene for detailed instructions on contributing to Flutter.

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@github-actions github-actions bot added the engine flutter/engine related. See also e: labels. label Sep 12, 2025
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Code Review

This pull request correctly fixes an issue where the engineId was not being preserved during a hot restart. The changes involve caching the engineId in the Engine from the RunConfiguration and then using this cached value to populate the new RunConfiguration during a hot restart. The change is logical and includes a new unit test to verify the behavior. I've added one suggestion to use std::move in a setter to align with modern C++ best practices.

engine/src/flutter/shell/common/run_configuration.cc
Comment on lines +108 to 110
void RunConfiguration::SetEngineId(std::optional<int64_t> engine_id) {
engine_id_ = engine_id;
}
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medium

For better performance and to follow modern C++ idioms, it's preferable to use std::move here.1 Since the engine_id parameter is passed by value and then stored in a member variable, moving it avoids an unnecessary copy when the argument is an rvalue.

Suggested change
void RunConfiguration::SetEngineId(std::optional<int64_t> engine_id) {
engine_id_ = engine_id;
}
void RunConfiguration::SetEngineId(std::optional<int64_t> engine_id) {
engine_id_ = std::move(engine_id);
}

Style Guide References

Footnotes

  1. The Google C++ Style Guide recommends passing parameters by value and moving them if the function needs to take ownership, which is the case here. ↩

@matanlurey matanlurey added the autosubmit Merge PR when tree becomes green via auto submit App label Sep 12, 2025
@auto-submit auto-submit bot merged commit 51c836f into flutter:flutter-3.37-candidate.0 Sep 12, 2025
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