description

iOS has support for os_signposts which gives allows you to identify certain regions of activity inside of Instruments. Dart appears to have support for emitting os_signpost events, but there is no way I can determine to enable it for Flutter projects.

It is my understanding that --trace-systrace is supposed to turn them on, but they don't.

Ideally there should be a way to make sure they are enabled when launching from Instruments as well. Typically this is done on iOS by caching the last arguments for launching the app from the command line.

steps to reproduce

1. flutter run --profile --trace-systrace
2. attach Instruments to the running process
3. tap around the app to make it update

Notice that no "Points of interest" are generated.

doctor

[✓] Flutter (Channel unknown, 3.1.0-0.0.pre.1072, on macOS 12.4 21F79
    darwin-x64, locale en-US)
    • Flutter version 3.1.0-0.0.pre.1072 at /Users/aaclarke/dev/flutter
    • Upstream repository unknown
    • Framework revision ff110fb958 (48 minutes ago), 2022-06-02 13:11:28 -0700
    • Engine revision 00a64bf4f2
    • Dart version 2.18.0 (build 2.18.0-163.0.dev)
    • DevTools version 2.13.1

fixes

• tool: Pass run and drive --trace-systrace for iOS #105321
• engine: Added plist flag for enabling trace-systrace. engine#33889
• dart: os_signposts aren't showing up correctly in Instruments dart-lang/sdk#49178