widget_preview_scaffold/build folder can grow very large #179139
Description
Steps to reproduce
I was cleaning up a disk (after running out of space!) and found that some of the widget preview build folders were very large.
I don't have good steps to reproduce because this happened over time, but (based on a brief chat with @bkonyi) I suspect if you use the widget preview a lot and trigger lots of reloads, this will happen.
Expected results
If these folders are created for each build/reload, the old versions should be cleaned up.
Actual results
The files just build up over time.
Code sample
N/A
Screenshots or Video
Logs
N/A
Flutter Doctor output
Doctor output
Note: These files built up over time, so may not have come from this specific version of Flutter.
[!] Flutter (Channel master, 3.39.0-1.0.pre-302, on Microsoft Windows [Version 10.0.26100.7171], locale en-GB) [2.5s]
• Flutter version 3.39.0-1.0.pre-302 on channel master at D:\Dev\Google\Flutter\Flutter main
! Warning: `dart` on your path resolves to D:\Tools\Dart\Stable\bin\dart.exe, which is not inside your current Flutter SDK checkout at
D:\Dev\Google\Flutter\Flutter main. Consider adding D:\Dev\Google\Flutter\Flutter main\bin to the front of your path.
! Upstream repository git@github.com:DanTup/flutter.git is not a standard remote.
Set environment variable "FLUTTER_GIT_URL" to git@github.com:DanTup/flutter.git to dismiss this error.
• Framework revision fde117b7b1 (2 hours ago), 2025-11-26 08:17:53 -0500
• Engine revision fde117b7b1
• Dart version 3.11.0 (build 3.11.0-169.0.dev)
• DevTools version 2.52.0
• Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop, enable-android, enable-ios, cli-animations,
enable-native-assets, omit-legacy-version-file, enable-lldb-debugging, enable-uiscene-migration
• If those were intentional, you can disregard the above warnings; however it is recommended to use "git" directly to perform update checks and
upgrades.
[✓] Windows Version (11 Pro 64-bit, 24H2, 2009) [871ms]
[!] Android toolchain - develop for Android devices (Android SDK version 35.0.0) [2.2s]
• Android SDK at C:\Users\danny\AppData\Local\Android\sdk
• Emulator version 35.4.9.0 (build_id 13025442) (CL:N/A)
• Platform android-36, build-tools 35.0.0
• Java binary at: C:\Program Files\Android\Android Studio\jbr\bin\java
This is the JDK bundled with the latest Android Studio installation on this machine.
To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
• Java version OpenJDK Runtime Environment (build 21.0.6+-13355223-b631.42)
! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses
[✓] Chrome - develop for the web [62ms]
• Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe
[✓] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.10.5) [62ms]
• Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Community
• Visual Studio Community 2022 version 17.10.35122.118
• Windows 10 SDK version 10.0.26100.0
[✓] Connected device (3 available) [146ms]
• Windows (desktop) • windows • windows-x64 • Microsoft Windows [Version 10.0.26100.7171]
• Chrome (web) • chrome • web-javascript • Google Chrome 142.0.7444.176
• Edge (web) • edge • web-javascript • Microsoft Edge 142.0.3595.80
[✓] Network resources [202ms]
• All expected network resources are available.
! Doctor found issues in 2 categories.