fix(windows): unblock release build on MSVC 14.51 coroutine hard error

[ByYudkowskysTentacle]

Problem

flutter build windows --release fails on windows-latest. Android, iOS and Linux are unaffected.

...\MSVC\14.51.36231\include\experimental\coroutine(37,1): error C2338:
static assertion failed: 'error STL1011: The /await compiler option,
<experimental/coroutine>, <experimental/generator>, and <experimental/resumable>
are deprecated by Microsoft and will be REMOVED SOON. ... You can define
_SILENCE_EXPERIMENTAL_COROUTINE_DEPRECATION_WARNINGS to suppress this error for now.'

Failing projects: flutter_inappwebview_windows_plugin and permission_handler_windows_plugin.

MSVC 14.51 (Visual Studio 2026) promoted the <experimental/coroutine> deprecation from a warning to a hard static_assert. This is a toolchain change on the hosted runner, so the build broke with no code change in the repo.

Why those two plugins

Both reach the experimental header through C++/WinRT, for different reasons:

• flutter_inappwebview_windows compiles as C++17, so __cpp_lib_coroutine is undefined and <winrt/base.h> falls back to <experimental/coroutine>.
• permission_handler_windows builds with /await, which selects the pre-C++20 coroutine machinery outright.

Neither is patchable in-repo: both live under windows/flutter/ephemeral/.plugin_symlinks/ and are regenerated by flutter pub get.

Fix

One line in windows/CMakeLists.txt, beside the existing add_definitions(-DUNICODE -D_UNICODE):

add_definitions(-D_SILENCE_EXPERIMENTAL_COROUTINE_DEPRECATION_WARNINGS)

add_definitions sets a directory property that subdirectories inherit when they're added, and the plugins are added further down via include(flutter/generated_plugins.cmake). Setting it here reaches each plugin target, including flutter_inappwebview_windows, which does not call apply_standard_settings (it defines its own copy to drop /WX), so patching that function alone would miss it.

Also points the Inno Setup shortcuts at OpenlibExtended.exe, matching BINARY_NAME. They previously said OpenLibExtended.exe; NTFS resolved that case-insensitively, but this seemed like a better-safe-than-sorry situation.

Testing

• Windows build succeeds on windows-latest, Flutter 3.38.6, MSVC 14.51.36231
• Inno Setup produces openlib-windows-x64-1.0.11.exe; the bundle contains all five plugin DLLs plus Webview2Loader.dll
• Installer run on Windows: app launches, webview and permission flows work, book download tested successfully

No new dependencies, no app code touched. 2 files changed, +13 −3.

[warreth]

Book download tested? so downloading of books is working?

[ByYudkowskysTentacle]

Book download tested? so downloading of books is working?

Yes! All tests downloaded successfully, whatever you did seems to be working on Windows. The user gets a pop-up with the page itself on search and on title-selection, so from a UX point of view that's not ideal, but it works, and that's an improvement over the last version. I can take a swing at resolving that if you'd like (though I am still only getting familiar with the codebase).