Flutter 3.19.x made wayland an unconditional requirement

[aduskett]

When compiling without Wayland, the following errors occur:

flutter/third_party/swiftshader/src/WSI/libWaylandClient.hpp:18:10: fatal error: 'wayland-client.h' file not found
../../flutter/third_party/swiftshader/src/WSI/WaylandSurfaceKHR.hpp:22:10: fatal error: 'wayland-client.h' file not found

I am not sure what exact commit caused the above error, but the above does not happen when compiling Flutter 3.16.8 using the Buildroot linux embedded sdk when cross-compiling an arm64 build

My testing was done via the Buildroot embedded Linux SDK and updating from Flutter 3.16.8 to 3.19.2 cross-compiling an ARM64 build of Flutter using an X64 host without Wayland.

Edit: Here are the configure commands:

>>> flutter-engine 3.16.8 Configuring
/usr/bin/sed -i -e "s%vulkan_use_x11.*%vulkan_use_x11 = false%g" output/build/flutter-engine-3.16.8/build_overrides/vulkan_headers.gni
/usr/bin/sed -i -e "s%vulkan_use_wayland.*%vulkan_use_wayland = false%g" output/build/flutter-engine-3.16.8/build_overrides/vulkan_headers.gni


cd output/build/flutter-engine-3.16.8 && rm -rf output/build/flutter-engine-3.16.8/out/linux_release_arm64 && PATH=output/host/share/depot_tools:"output/host/bin:output/host/sbin:/home/adam/.local/bin:/home/adam/Applications/bin:/home/adam/Applications/depot_tools:/home/adam/Applications/scripts:/snap/bin:/opt/zscaler/bin/:/usr/local/bin:/usr/lib64/ccache:/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/var/lib/snapd/snap/bin" PUB_CACHE=dl/br-flutter-pub-cache HOME=output/host/share/flutter/sdk ./flutter/tools/gn \
--clang \
--embedder-for-target \
--linux-cpu arm64 \
--no-build-embedder-examples \
--no-clang-static-analyzer \
--no-enable-unittests \
--no-goma \
--no-prebuilt-dart-sdk \
--no-stripped \
--use-mallinfo2 \
--runtime-mode release \
--target-os linux \
--target-sysroot output/host/aarch64-buildroot-linux-gnu/sysroot \
--target-toolchain output/build/flutter-engine-3.16.8/buildtools/linux-x64/clang \
--target-triple aarch64-unknown-linux-gnu \
--no-lto \
--enable-impeller-opengles \
--no-build-glfw-shell \
--disable-desktop-embeddings

[aduskett]

I have yet to figure out what has caused this issue. At this point, I assume it's because of the update to swiftshader.

[aduskett]

It looks like flutter/engine@1750693 is the culprit.
Specifically, this file: https://github.com/flutter/engine/blame/main/build_overrides/vulkan_headers.gni

[aduskett]

Thanks to @jwinarske for tracking down the real culprit:
meta-flutter/meta-flutter#452 (comment)

> @aduskett Looks like build parameters are not correctly being passed to swiftshader. Let me take a look at the swiftshader tree

meta-flutter/meta-flutter#452 (comment)

> @aduskett In swiftshader tip of tree there is support for either DirectFB or Direct2Display (D2D). It should be the same for flutter-engine swiftshader DEP commit.
> 
> ```
> if(SWIFTSHADER_BUILD_WSI_DIRECTFB)
>     find_library(DIRECTFB directfb)
>     find_path(DIRECTFB_INCLUDE_DIR directfb/directfb.h)
> endif(SWIFTSHADER_BUILD_WSI_DIRECTFB)
> if(SWIFTSHADER_BUILD_WSI_D2D)
>     find_library(D2D drm)
>     find_path(D2D_INCLUDE_DIR libdrm/drm.h)
> endif(SWIFTSHADER_BUILD_WSI_D2D)
> ...
> if(LINUX)
>     option_if_not_defined(SWIFTSHADER_BUILD_WSI_XCB "Build the XCB WSI support" TRUE)
>     option_if_not_defined(SWIFTSHADER_BUILD_WSI_WAYLAND "Build the Wayland WSI support" TRUE)
>     option_if_not_defined(SWIFTSHADER_BUILD_WSI_DIRECTFB "Build the DirectFB WSI support" FALSE)
>     option_if_not_defined(SWIFTSHADER_BUILD_WSI_D2D "Build the Direct-to-Display WSI support" FALSE)
> endif()
> ```
> 
> You just need to add some logic in flutter engine land to set it correctly.

meta-flutter/meta-flutter#452 (comment)

> In here: flutter/third_party/swiftshader/src/Vulkan/BUILD.gn
> 
> ```
>     if (ozone_platform_x11) {
>       defines += [ "VK_USE_PLATFORM_XCB_KHR" ]
>     }
>     if (ozone_platform_wayland) {
>       defines += [ "VK_USE_PLATFORM_WAYLAND_KHR" ]
>     }
> ```
> 
> It skips the desired options all together.
> 
> Work also needed in here: flutter/third_party/swiftshader/src/WSI/BUILD.gn

meta-flutter/meta-flutter#452 (comment)

> @aduskett Changes would need to be made upstream in the swiftshader repo, then it would eventually get picked up by the flutter engine master. Until then you would need to patch it. Might be easier to patch.

So, the problem is that Swiftshader and Flutter do not pass proper build flags to Swiftshader. Do you have any thoughts?

[aduskett]

After digging around, here is the real culprit:
https://github.com/flutter/buildroot/blob/092e19a7caead03d25b161f33cff6ca520630aac/build/config/BUILDCONFIG.gn#L306

Specifically:
flutter/buildroot@d01da27

I am fixing the problem by running
sed "s%ozone_platform_x11.*%ozone_platform_x11 = false%g" -i build/config/BUILDCONFIG.gn and
sed "s%ozone_platform_wayland.*%ozone_platform_wayland = false%g" -i build/config/BUILDCONFIG.gn as a pre-configure hook if X11 or Wayland are unselected.

It's unfortunate that these values are hard coded, as Flutter works properly without Wayland or X11.