FlClash/.agents/flutter-upgrade.md

Flutter Upgrade Checklist

Read this before changing FLUTTER_VERSION in .github/workflows/build.yaml or .fvmrc. Each entry is a workaround tied to a Flutter bug: what it does, where it lives, and what has to be true before it can go. Remove an entry together with its workaround; add one whenever a new workaround is pinned to the SDK.

Stable cadence

Flutter ships a stable release about once a quarter, three minor versions apart (3.41 in February, 3.44 in May, 3.47 in August 2026). The two minors in between (3.48, 3.49) are beta only, so a fix that lands on main reaches stable in the next multiple, 3.50, expected around mid-November 2026. Hotfix releases (3.47.x) carry only cherry-picks listed in the SDK's CHANGELOG.md.

Impeller disabled on Intel macOS release builds

• Bug: flutter/flutter#191538. From 3.47, when Impeller became the default desktop renderer, Intel (x86_64) Macs flicker across the whole window while scrolling or animating, and text can render garbled. Apple Silicon is not affected.
• Fix upstream: landed on main before 2026-08-25 and verified on 3.48.0-1.0.pre-404; it is not in any 3.47.x hotfix (checked through 3.47.6).
• Workaround: the release job for macos-15-intel (arch: amd64) runs plutil -replace FLTEnableImpeller -bool NO macos/Runner/Info.plist before dart setup.dart, so only the Intel DMG falls back to Skia. The checked-in Info.plist does not set the key, so local builds and the arm64 DMG keep Impeller. The macOS embedder reads the key at launch in FlutterDartProject.mm (enableImpeller), release builds included.
• Side effect: Skia on Intel renders blur, shadows and text slightly differently; judge Intel-only visual reports against Skia, not Impeller.
• Remove when: FLUTTER_VERSION moves to a stable that contains the fix (3.50 or later, or a 3.47.x whose changelog lists #191538). Before dropping the step, build the Intel DMG without it and scroll the proxies and dashboard pages on an Intel Mac with its integrated GPU driving the built-in display; an external display can switch to the discrete GPU and hide the flicker.

Wrong-size back buffer on macOS

• Bug: flutter/flutter#185394. removeSurfaceForSize: in the macOS engine's FlutterSurfaceManager.mm hands out the youngest idle cached surface without checking its size. When the window flips between sizes while the window server still holds the previous surface, which dragging a window edge back and forth does, a request for one size gets a surface of another. Impeller's Metal texture then disagrees with its descriptor, the render target drops it, and Canvas::SetupRenderPass dereferences a null texture on the raster thread. Debug builds log The texture and its descriptor disagree about its size and Store action needs resolve but no valid resolve texture specified first; release builds just crash.
• Fix upstream: flutter/flutter#192522, still open; 3.47.6 ships the same FlutterSurfaceManager.mm as 3.47.4.
• Workaround: BackBufferCacheGuard in the window plugin's macos/window/Sources/window/BackBufferCacheGuard.swift, installed from WindowPlugin.register, replaces -[FlutterBackBufferCache removeSurfaceForSize:] at runtime and answers nil when the cached surface is not the requested size, so the engine allocates a new one. It does nothing if the engine no longer has that class or selector.
• Remove when: FLUTTER_VERSION moves to a stable that contains #192522 (check the SDK CHANGELOG.md for a 3.47.x cherry-pick). Before dropping it, run a debug build without the guard on that SDK and drag a window edge back and forth for a minute; neither validation line may appear.

Windows view visibility forwarded by the runner

• Bug: the Windows embedder's WindowsLifecycleManager counts the Flutter view as a window of its own and keeps it visible until the view is sized to zero. Hiding the top-level window never resizes the view, and the window plugin keeps it sized while minimized, so the app was never told hidden: animations kept rendering in the tray and appVisibleProvider stayed true.
• Workaround: WindowPluginForwardVisibility in the window plugin's windows/include/window/window_plugin_runner.h hands the top-level window's WM_SHOWWINDOW and WM_SIZE to ProcessExternalWindowMessage for the view's HWND, so the view shows and hides with its window. FlutterWindow::MessageHandler in windows/runner/flutter_window.cpp calls it before HandleTopLevelWindowProc; the Flutter runner template has no such call, so keep it when regenerating the runner.
• Remove when: the engine hides the view together with its top-level window. Check with the proxy running and the window focused: hiding it to the tray and minimizing it must each log AppLifecycleState.hidden.

macOS activation resumes a hidden window

• Bug: handleWillBecomeActive in the macOS engine's FlutterEngine.mm resumes when any window in NSApp.windows is visible, and the tray's NSStatusBarWindow always is. Activating the app while its window was minimized or hidden, such as Cmd-Tab back to a minimized window, reported resumed, and the next deactivation inactive, so frames ran until the window was shown again.
• Workaround: the window plugin observes will-become-active and will-resign-active and, once the engine has answered, sends AppLifecycleState.hidden on flutter/lifecycle while its window is not visible (applicationActivityChanged in WindowPlugin.swift). A window brought back without another activation change would then wait on an occlusion notification macOS does not always post, keeping its last frame, so show and a deminiaturize hand the state back (windowBecameVisible).
• Remove when: the engine ignores status item windows on activation. Check without the workaround: minimize the window, switch to another app, then Cmd-Tab back without restoring it; the log must stay at AppLifecycleState.hidden.

Linux minimize on Wayland reads as inactive

• Bug: the Linux engine reports hidden for GDK_WINDOW_STATE_ICONIFIED, but xdg-shell has no minimized state, so GTK 3 never sets it on Wayland. A minimized window reported only its focus loss, as inactive, and kept rendering at the display rate (GNOME 46).
• Workaround: the window plugin's Linux minimize records the time, and a focus loss within 500 ms of it sends AppLifecycleState.hidden. Its window-state-event handler is connected after the engine's, so that message follows the engine's inactive; the compositor focuses the window when it restores it, which the engine reports as resumed. A minimize the compositor starts itself (Super+H, the dock) is not covered.
• Remove when: the Linux engine reports minimized windows on Wayland, which needs GTK 4 or xdg-shell's suspended state. Check in a GNOME Wayland session without the workaround: minimizing from the caption button must log AppLifecycleState.hidden.

Liquid glass saves around the transform of a blurring layer

• Bug: not filed upstream. On 3.47 Impeller scales a saveLayer's image filter by a transform set inside the layer that is still in effect when the layer is restored. A host's capture shrinks each pane's slot inside the layer that blurs it, so its blur vanished at a quarter scale and spread half again as far at 1.5.
• Workaround: _LiquidGlassHostLayer._snapshot sets each slot's transform inside a save of its own, and each band's offset, restored before the layer is.
• Remove when: without that save, the frosted-pane case of test/widgets/liquid_glass_host_test.dart passes under flutter test --enable-impeller.