package/flutter-engine: new package

There are many issues with this package:

- The release tarballs from https://github.com/flutter/engine are in no state
  to compile. They are only for the use of gclient to download a source
  directory structure suitable to build the Flutter engine! If you download,
  extract and attempt to run `./tools/gn --no-goma --no-prebuilt-dart-sdk`, you
  receive the error message:
  `No such file or directory: 'flutter/flutter/third_party/gn/gn.'

  But wait! Wasn't the gn binary just called? No, that's a wrapper in the
  Flutter source tree that formats arguments to call the real gn binary.
  The real gn is not provided in the tarball but is downloaded via gclient
  (among many other supporting repositories.)

  Even worse, the flutter buildsystem depends on the .git dirs being present.
  (https://github.com/meta-flutter/meta-flutter/issues/271) This dependency
  means it is not possible to create a reproducible tarball from the downloaded
  sources, which is why there is no .hash file provided.

  I have asked the flutter project to release full tarballs suitable for
  compiling here: https://github.com/flutter/flutter/issues/130734

- Flutter engine includes a patched copy of clang that must be used to compile.
  Using a Buildroot-build clang results in linking warning and errors.
  As such, we depend on LLVM_ARCH_SUPPORTS but use the included clang for
  building. On the plus side, this saves time having to compile clang.

- flutter-engine relies on the "PUB_CACHE", that is provided by flutter-sdk,
  so we need a build dependency, even if no tool from host-flutter-sdk-bin
  is used to build flutter-engine

Tested with:
  - Debian 11 and 12
  - Ubuntu 18.04, 20.04, and 22.04
  - Fedora 38
  - Per-package directories

Signed-off-by: Adam Duskett <adam.duskett@amarulasolutions.com>
[yann.morin.1998@free.fr:
  - search gclient.py from PATH
  - indent shell script with 4 spaces
  - reorganise schell script with prepare/cleanup
  - tweak comment about weirdness of flutter buildsystem
  - use suitable-extactor and TAR_OPTIONS
  - use FLUTTER_SDK_BIN_PUB_CACHE
  - add dependency to host-futter-sdk-bin (Adam)
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

DEVELOPERS

@@ -33,6 +33,7 @@ F:	package/vulkan-tools/
 
 N:	Adam Duskett <adam.duskett@amarulasolutions.com>
 F:	package/depot-tools/
+F:	package/flutter-engine/
 F:	package/flutter-sdk-bin/
 
 N:	Adam Heinrich <adam@adamh.cz>

package/Config.in

@@ -1586,6 +1586,7 @@ menu "Graphics"
 	source "package/exempi/Config.in"
 	source "package/exiv2/Config.in"
 	source "package/fltk/Config.in"
+	source "package/flutter-engine/Config.in"
 	source "package/fontconfig/Config.in"
 	source "package/freetype/Config.in"
 	source "package/gd/Config.in"

package/flutter-engine/0001-disable-pre-canned-sysroot.patch

@@ -0,0 +1,32 @@
+From 49a14e693124dc34f2cccbfb755d01a1198aa6bf Mon Sep 17 00:00:00 2001
+From: Joel Winarske <joel.winarsk@gmail.com>
+Date: Wed, 19 Jul 2023 15:24:22 -0700
+Subject: [PATCH] disable pre-canned sysroot
+
+Override should be enabled if a custom sysroot using --target-sysroot is
+specified. If --target-sysroot is not set, then it should default to the
+pre-canned sysroot.
+
+Upstream: https://github.com/flutter/flutter/issues/123073
+Signed-off-by: Joel Winarske <joel.winarsk@gmail.com>
+Signed-off-by: Adam Duskett <adam.duskett@amarulasolutions.com>
+---
+ build/config/sysroot.gni | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/build/config/sysroot.gni b/build/config/sysroot.gni
+index 7987e519d..1de694263 100644
+--- a/build/config/sysroot.gni
++++ b/build/config/sysroot.gni
+@@ -14,7 +14,7 @@ declare_args() {
+ 
+   # Whether to use the default sysroot when building for Linux, if an explicit
+   # sysroot isn't set.
+-  use_default_linux_sysroot = true
++  use_default_linux_sysroot = false
+ }
+ 
+ if (current_toolchain == default_toolchain && target_sysroot != "") {
+-- 
+2.41.0
+

package/flutter-engine/0002-remove-explicit-x11-dependency.patch

@@ -0,0 +1,33 @@
+From b1a5db9318ca33a03f2700758d5debad907d21b6 Mon Sep 17 00:00:00 2001
+From: Joel Winarske <joel.winarsk@gmail.com>
+Date: Wed, 19 Jul 2023 15:26:40 -0700
+Subject: [PATCH] remove explicit x11 dependency
+
+This is superfluous and may conflict with the actual rendering system used in
+gtk3 (e.g. wayland.)
+
+Upstream: https://github.com/flutter/flutter/issues/123073
+Signed-off-by: Joel Winarske <joel.winarske@gmail.com>
+Signed-off-by: Adam Duskett <adam.duskett@amarulasolutions.com>
+---
+ flutter/shell/platform/linux/config/BUILD.gn | 4 ----
+ 1 file changed, 4 deletions(-)
+
+diff --git a/flutter/shell/platform/linux/config/BUILD.gn b/flutter/shell/platform/linux/config/BUILD.gn
+index da0ac056b..70c7a0ea1 100644
+--- a/flutter/shell/platform/linux/config/BUILD.gn
++++ b/flutter/shell/platform/linux/config/BUILD.gn
+@@ -5,10 +5,6 @@
+ import("//build/config/linux/pkg_config.gni")
+ import("//flutter/shell/platform/glfw/config.gni")
+ 
+-pkg_config("x11") {
+-  packages = [ "x11" ]
+-}
+-
+ pkg_config("gtk") {
+   packages = [ "gtk+-3.0" ]
+ }
+-- 
+2.41.0
+

package/flutter-engine/0003-fix-toolchain-paths.patch

@@ -0,0 +1,40 @@
+From ca175ef5bf7f96db57fb5aa562602dc424fab81c Mon Sep 17 00:00:00 2001
+From: Joel Winarske <joel.winarsk@gmail.com>
+Date: Sun, 5 Mar 2023 10:43:02 -0800
+Subject: [PATCH] fix toolchain paths
+
+Flutter includes a copy of clang which is required to build. However, by
+default, build/toolchain/custom/BUILD.gn attempts to use several gcc utilities
+such as ar, readelf, nm, and strip. Change these to the proper llvm provided
+utility.
+
+Upstream: https://github.com/flutter/flutter/issues/123073
+
+Signed-off-by: Joel Winarske <joel.winarsk@gmail.com>
+Signed-off-by: Adam Duskett <adam.duskett@amarulasolutions.com>
+---
+ build/toolchain/custom/BUILD.gn | 4 +++++------
+ 1 file changed, 5 insertions(+), 6 deletions(-)
+
+diff --git a/build/toolchain/custom/BUILD.gn b/build/toolchain/custom/BUILD.gn
+index 65b1623..8b3f6f8 100644
+--- a/build/toolchain/custom/BUILD.gn
++++ b/build/toolchain/custom/BUILD.gn
+@@ -12,11 +12,11 @@ toolchain("custom") {
+   # these values in our scope.
+   cc = "${toolchain_bin}/clang"
+   cxx = "${toolchain_bin}/clang++"
+-  ar = "${toolchain_bin}/${custom_target_triple}-ar"
++  ar = "${toolchain_bin}/llvm-ar"
+   ld = "${toolchain_bin}/clang++"
+-  readelf = "${toolchain_bin}/${custom_target_triple}-readelf"
+-  nm = "${toolchain_bin}/${custom_target_triple}-nm"
+-  strip = "${toolchain_bin}/${custom_target_triple}-strip"
++  readelf = "${toolchain_bin}/llvm-readelf"
++  nm = "${toolchain_bin}/llvm-nm"
++  strip = "${toolchain_bin}/llvm-strip"
+ 
+   target_triple_flags = "--target=${custom_target_triple}"
+   sysroot_flags = "--sysroot ${custom_sysroot}"
+-- 
+2.39.2

package/flutter-engine/0004-pkg-config.py-do-not-prepend-sysroot-path.patch

@@ -0,0 +1,37 @@
+From 51e8fed854fd9d373bb9b20d7ed8e7cf6ef12312 Mon Sep 17 00:00:00 2001
+From: Adam Duskett <adam.duskett@amarulasolutions.com>
+Date: Wed, 19 Jul 2023 11:48:59 -0700
+Subject: [PATCH] pkg-config.py: do not prepend sysroot path
+
+Buildroot uses the standard PKG_CONFIG_SYSROOT_DIR variable, so what the
+pkg-config.py script is doing doesn't make sense. There is no need to prepend
+the sysroot, and flutter should let pkg-config use the PKG_CONFIG_SYSROOT_DIR
+variable.
+
+Without this patch, the pkg-config.py script double prepends the sysroot path.
+IE: output/host/.../sysroot/output/host/.../sysroot
+
+Upstream: https://github.com/flutter/flutter/issues/132152
+Signed-off-by: Adam Duskett <adam.duskett@amarulasolutions.com>
+---
+ build/config/linux/pkg-config.py | 4 +---
+ 1 file changed, 1 insertion(+), 3 deletions(-)
+
+diff --git a/build/config/linux/pkg-config.py b/build/config/linux/pkg-config.py
+index b4a6aff17..44ffdcaea 100644
+--- a/build/config/linux/pkg-config.py
++++ b/build/config/linux/pkg-config.py
+@@ -207,9 +207,7 @@ def main():
+   all_flags = flag_string.strip().split(' ')
+ 
+ 
+-  sysroot = options.sysroot
+-  if not sysroot:
+-    sysroot = ''
++  sysroot = ''
+ 
+   includes = []
+   cflags = []
+-- 
+2.41.0
+

package/flutter-engine/Config.in

@@ -0,0 +1,55 @@
+# Flutter includes a vender copy of clang which is mandatory to use for
+# compiling. These are the supported architectures.
+config BR2_PACKAGE_FLUTTER_ENGINE_ARCH_SUPPORTS
+	bool
+	default y if BR2_aarch64
+	default y if BR2_arm && !BR2_ARM_CPU_ARMV4 && !BR2_ARM_CPU_ARMV5
+	default y if BR2_x86_64
+
+config BR2_PACKAGE_FLUTTER_ENGINE
+	bool "flutter-engine"
+	depends on BR2_PACKAGE_FLUTTER_ENGINE_ARCH_SUPPORTS
+	depends on BR2_TOOLCHAIN_USES_GLIBC
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_5
+	depends on BR2_TOOLCHAIN_HAS_THREADS_NPTL # pthreads
+	depends on BR2_INSTALL_LIBSTDCPP
+	depends on !BR2_TOOLCHAIN_HAS_GCC_BUG_64735 # std::shared_future
+	depends on !BR2_STATIC_LIBS
+	depends on BR2_USE_WCHAR # std::wstring
+	depends on BR2_HOST_GCC_AT_LEAST_5
+	depends on BR2_PACKAGE_HAS_LIBGL || BR2_PACKAGE_HAS_LIBGLES
+	select BR2_PACKAGE_FREETYPE
+	select BR2_PACKAGE_HOST_DEPOT_TOOLS
+	select BR2_PACKAGE_ZLIB
+	help
+	  Flutter is Google's SDK for crafting beautiful, fast user
+	  experience for mobile, web, and desktop from a single
+	  codebase. Flutter works with existing code, is used by
+	  developers and organizations around the world, and is
+	  free and open source.
+
+	  The Flutter Engine is a portable runtime for hosting
+	  Flutter applications. It implements Flutter's core
+	  libraries, including animation and graphics, file and
+	  network I/O, accessibility support, plugin architecture,
+	  and a Dart runtime and compile toolchain. Most developers
+	  will interact with Flutter via the Flutter Framework,
+	  which provides a modern, reactive framework, and a rich
+	  set of platform, layout and foundation widgets.
+
+	  https://github.com/flutter/engine
+
+comment "flutter-engine needs an OpenGL or OpenGLES backend"
+	depends on BR2_PACKAGE_FLUTTER_ENGINE_ARCH_SUPPORTS
+	depends on !BR2_PACKAGE_HAS_LIBGL && !BR2_PACKAGE_HAS_LIBGLES
+
+comment "flutter-engine needs a glibc toolchain w/ wchar, C++, gcc >= 5, dynamic library, host gcc >= 5, NPTL"
+	depends on BR2_PACKAGE_FLUTTER_ENGINE_ARCH_SUPPORTS
+	depends on !BR2_TOOLCHAIN_USES_GLIBC || !BR2_TOOLCHAIN_HAS_THREADS_NPTL \
+		|| !BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_GCC_AT_LEAST_5 \
+		|| BR2_STATIC_LIBS || !BR2_USE_WCHAR \
+		|| !BR2_HOST_GCC_AT_LEAST_5
+
+comment "flutter-engine needs a toolchain not affected by GCC bug 64735"
+	depends on BR2_PACKAGE_FLUTTER_ENGINE_ARCH_SUPPORTS
+	depends on BR2_TOOLCHAIN_HAS_GCC_BUG_64735

package/flutter-engine/dot-gclient

@@ -0,0 +1,13 @@
+# Definition file to download flutter-engine
+# Inspired by the output of meta-flutter/lib/gn.py
+
+solutions = [{
+    "managed": False,
+    "name": "src/flutter",
+    "url": "https://github.com/flutter/engine.git@!FLUTTER_VERSION!",
+    "custom_vars": {
+        "download_android_deps": False,
+        "download_windows_deps": False,
+        "download_linux_deps": False
+    },
+}]

package/flutter-engine/flutter-engine.mk

@@ -0,0 +1,239 @@
+################################################################################
+#
+# flutter-engine
+#
+################################################################################
+
+# Flutter-engine has a release on the GitHub page. However, that release is
+# only for Google. Its intended purpose is for the gclient tool provided by
+# Google in their depot-tools package. To use the source code, we must use
+# gclient to download the flutter-engine source code along with several other
+# projects. Unfortunately, the Buildroot download system does not have the
+# capability of using gclient, and considering this package is the only
+# package that uses gclient, we side-step the entire download process and
+# perform the following steps if a tarball does not exist already:
+#
+#  - Copy the pre-made gclient config file to a temporary scratch directory.
+#  - Run gclient sync to generate a source directory with the proper
+#    flutter-engine source code in the correct places.
+#  - Create a source tarball.
+#  - Copy the source tarball to the $(FLUTTER_ENGINE_DL_DIR) directory.
+#
+# There is no hash provided, as the gn binary (used for configuration) relies
+# on the .git directories. As such, a reproducible tarball is not possible.
+FLUTTER_ENGINE_VERSION = 3.13.4
+
+# There is nothing for Buildroot to download. This is handled by gclient.
+FLUTTER_ENGINE_SITE =
+FLUTTER_ENGINE_SOURCE =
+FLUTTER_ENGINE_LICENSE = BSD-3-Clause
+FLUTTER_ENGINE_LICENSE_FILES = LICENSE
+FLUTTER_ENGINE_TARBALL_PATH = $(FLUTTER_ENGINE_DL_DIR)/flutter-$(FLUTTER_ENGINE_VERSION).tar.gz
+FLUTTER_ENGINE_INSTALL_STAGING = YES
+FLUTTER_ENGINE_DOWNLOAD_DEPENDENCIES = host-depot-tools
+FLUTTER_ENGINE_DEPENDENCIES = \
+	host-flutter-sdk-bin \
+	host-ninja \
+	host-pkgconf \
+	freetype \
+	zlib
+
+# Dispatch all architectures of flutter
+# FLUTTER_ENGINE_TARGET_TRIPPLE must match the directory name found in
+# buildtools/linux-x64/clang/lib/clang/*/lib
+ifeq ($(BR2_aarch64),y)
+FLUTTER_ENGINE_TARGET_ARCH = arm64
+FLUTTER_ENGINE_TARGET_TRIPPLE = aarch64-unknown-linux-gnu
+else ifeq ($(BR2_arm)$(BR2_armeb),y)
+FLUTTER_ENGINE_TARGET_ARCH = arm
+FLUTTER_ENGINE_TARGET_TRIPPLE = armv7-unknown-linux-gnueabihf
+else ifeq ($(BR2_x86_64),y)
+FLUTTER_ENGINE_TARGET_ARCH = x64
+FLUTTER_ENGINE_TARGET_TRIPPLE = x86_64-unknown-linux-gnu
+endif
+
+ifeq ($(BR2_ENABLE_RUNTIME_DEBUG),y)
+FLUTTER_ENGINE_RUNTIME_MODE=debug
+else
+FLUTTER_ENGINE_RUNTIME_MODE=release
+endif
+
+FLUTTER_ENGINE_BUILD_DIR = \
+	$(@D)/out/linux_$(FLUTTER_ENGINE_RUNTIME_MODE)_$(FLUTTER_ENGINE_TARGET_ARCH)
+
+FLUTTER_ENGINE_INSTALL_FILES = libflutter_engine.so
+
+# Flutter engine includes a bundled patched clang that must be used for
+# compiling or else there are linking errors.
+FLUTTER_ENGINE_CLANG_PATH = $(@D)/buildtools/linux-x64/clang
+
+FLUTTER_ENGINE_CONF_OPTS = \
+	--clang \
+	--embedder-for-target \
+	--linux-cpu $(FLUTTER_ENGINE_TARGET_ARCH) \
+	--no-build-embedder-examples \
+	--no-clang-static-analyzer \
+	--no-enable-unittests \
+	--no-goma \
+	--no-prebuilt-dart-sdk \
+	--no-stripped \
+	--runtime-mode $(FLUTTER_ENGINE_RUNTIME_MODE) \
+	--target-os linux \
+	--target-sysroot $(STAGING_DIR) \
+	--target-toolchain $(FLUTTER_ENGINE_CLANG_PATH) \
+	--target-triple $(FLUTTER_ENGINE_TARGET_TRIPPLE)
+
+ifeq ($(BR2_arm)$(BR2_armeb),y)
+FLUTTER_ENGINE_CONF_OPTS += \
+	--arm-float-abi $(call qstrip,$(BR2_GCC_TARGET_FLOAT_ABI))
+endif
+
+# We must specify a full path to ccache and a full path to the flutter-engine
+# provided clang in order to use ccache, or else flutter-engine will error out
+# attempting to find ccache in the target-toolchain provided path.
+ifeq ($(BR2_CCACHE),y)
+define FLUTTER_ENGINE_COMPILER_PATH_FIXUP
+	$(SED) "s%cc =.*%cc = \"$(HOST_DIR)/bin/ccache $(FLUTTER_ENGINE_CLANG_PATH)/bin/clang\""%g \
+		$(@D)/build/toolchain/custom/BUILD.gn
+
+	$(SED) "s%cxx =.*%cxx = \"$(HOST_DIR)/bin/ccache $(FLUTTER_ENGINE_CLANG_PATH)/bin/clang++\""%g \
+		$(@D)/build/toolchain/custom/BUILD.gn
+endef
+FLUTTER_ENGINE_PRE_CONFIGURE_HOOKS += FLUTTER_ENGINE_COMPILER_PATH_FIXUP
+endif
+
+ifeq ($(BR2_ENABLE_LTO),y)
+FLUTTER_ENGINE_CONF_OPTS += --lto
+else
+FLUTTER_ENGINE_CONF_OPTS += --no-lto
+endif
+
+ifeq ($(BR2_OPTIMIZE_0),y)
+FLUTTER_ENGINE_CONF_OPTS += --unoptimized
+endif
+
+# There is no --disable-fontconfig option.
+ifeq ($(BR2_PACKAGE_FONTCONFIG),y)
+FLUTTER_ENGINE_DEPENDENCIES += fontconfig
+FLUTTER_ENGINE_CONF_OPTS += --enable-fontconfig
+endif
+
+ifeq ($(BR2_PACKAGE_HAS_LIBGL),y)
+FLUTTER_ENGINE_DEPENDENCIES += libgl
+endif
+
+ifeq ($(BR2_PACKAGE_HAS_LIBGLES),y)
+FLUTTER_ENGINE_DEPENDENCIES += libgles
+endif
+
+ifeq ($(BR2_PACKAGE_LIBGLFW),y)
+FLUTTER_ENGINE_DEPENDENCIES += libglfw
+FLUTTER_ENGINE_CONF_OPTS += --build-glfw-shell
+else
+FLUTTER_ENGINE_CONF_OPTS += --no-build-glfw-shell
+endif
+
+ifeq ($(BR2_PACKAGE_LIBGTK3),y)
+FLUTTER_ENGINE_DEPENDENCIES += libgtk3
+FLUTTER_ENGINE_INSTALL_FILES += libflutter_linux_gtk.so
+else
+FLUTTER_ENGINE_CONF_OPTS += --disable-desktop-embeddings
+endif
+
+# There is no --disable-vulkan option
+ifeq ($(BR2_PACKAGE_MESA3D_VULKAN_DRIVER),y)
+FLUTTER_ENGINE_CONF_OPTS += --enable-vulkan
+endif
+
+ifeq ($(BR2_PACKAGE_XORG7)$(BR2_PACKAGE_LIBXCB),yy)
+FLUTTER_ENGINE_DEPENDENCIES += libxcb
+else
+define FLUTTER_ENGINE_VULKAN_X11_SUPPORT_FIXUP
+	$(SED) "s%vulkan_use_x11.*%vulkan_use_x11 = false%g" -i \
+		$(@D)/build_overrides/vulkan_headers.gni
+endef
+FLUTTER_ENGINE_PRE_CONFIGURE_HOOKS += FLUTTER_ENGINE_VULKAN_X11_SUPPORT_FIXUP
+endif
+
+ifeq ($(BR2_PACKAGE_WAYLAND),y)
+FLUTTER_ENGINE_DEPENDENCIES += wayland
+else
+define FLUTTER_ENGINE_VULKAN_WAYLAND_SUPPORT_FIXUP
+	$(SED) "s%vulkan_use_wayland.*%vulkan_use_wayland = false%g" \
+		$(@D)/build_overrides/vulkan_headers.gni
+endef
+FLUTTER_ENGINE_PRE_CONFIGURE_HOOKS += FLUTTER_ENGINE_VULKAN_WAYLAND_SUPPORT_FIXUP
+endif
+
+# Generate a tarball if one does not already exist.
+define FLUTTER_ENGINE_GENERATE_TARBALL
+	PATH=$(HOST_DIR)/share/depot_tools:$(BR_PATH) \
+	PYTHONPATH=$(HOST_DIR)/lib/python$(PYTHON3_VERSION_MAJOR) \
+	PUB_CACHE=$(FLUTTER_SDK_BIN_PUB_CACHE) \
+	$(FLUTTER_ENGINE_PKGDIR)/gen-tarball \
+		--dot-gclient $(TOPDIR)/$(FLUTTER_ENGINE_PKGDIR)/dot-gclient \
+		--jobs $(PARALLEL_JOBS) \
+		--scratch-dir $(@D)/dl-tmp \
+		--tarball-dl-path $(FLUTTER_ENGINE_TARBALL_PATH) \
+		--version $(FLUTTER_ENGINE_VERSION)
+endef
+FLUTTER_ENGINE_POST_DOWNLOAD_HOOKS += FLUTTER_ENGINE_GENERATE_TARBALL
+
+define FLUTTER_ENGINE_EXTRACT_CMDS
+	$(call suitable-extractor,$(FLUTTER_ENGINE_TARBALL_PATH)) $(FLUTTER_ENGINE_TARBALL_PATH) \
+	| $(TAR) --strip-components=1 -C $(@D) $(TAR_OPTIONS) -
+endef
+
+define FLUTTER_ENGINE_CONFIGURE_CMDS
+	cd $(@D) && \
+		rm -rf $(FLUTTER_ENGINE_BUILD_DIR) && \
+		PATH=$(HOST_DIR)/share/depot_tools:$(BR_PATH) \
+		PUB_CACHE=$(FLUTTER_SDK_BIN_PUB_CACHE) \
+		./flutter/tools/gn \
+			$(FLUTTER_ENGINE_CONF_OPTS)
+endef
+
+define FLUTTER_ENGINE_BUILD_CMDS
+	cd $(@D) && \
+		PATH=$(HOST_DIR)/share/depot_tools:$(BR_PATH) \
+		PUB_CACHE=$(FLUTTER_SDK_BIN_PUB_CACHE) \
+		$(HOST_DIR)/bin/ninja \
+			-j $(PARALLEL_JOBS) \
+			-C $(FLUTTER_ENGINE_BUILD_DIR)
+endef
+
+# Flutter-engine builds several host applications use for flutter development.
+# One of those applications is gen_snapshot, which turns applications into
+# usable .so files for the target architecture. Compiling a host version of
+# flutter-engine would result in binaries producing host-architecture
+# flutter applications .so files. As such, copy gen_snapshot to the host
+# directory here and name it flutter_gen_snapshot for clarity.
+FLUTTER_ENGINE_GEN_SNAPSHOT = $(HOST_DIR)/bin/flutter_gen_snapshot
+define FLUTTER_ENGINE_INSTALL_GEN_SNAPSHOT
+	$(INSTALL) -D -m 0755 $(FLUTTER_ENGINE_BUILD_DIR)/clang_x64/gen_snapshot \
+		$(HOST_DIR)/bin/flutter_gen_snapshot
+endef
+FLUTTER_ENGINE_POST_INSTALL_STAGING_HOOKS += FLUTTER_ENGINE_INSTALL_GEN_SNAPSHOT
+
+define FLUTTER_ENGINE_INSTALL_STAGING_CMDS
+	$(foreach i,$(FLUTTER_ENGINE_INSTALL_FILES),
+		$(INSTALL) -D -m 0755 $(FLUTTER_ENGINE_BUILD_DIR)/so.unstripped/$(i) \
+			$(STAGING_DIR)/usr/lib/$(i); \
+	)
+	$(INSTALL) -D -m 0755 $(FLUTTER_ENGINE_BUILD_DIR)/flutter_embedder.h \
+		$(STAGING_DIR)/usr/include/flutter_embedder.h
+
+	$(INSTALL) -D -m 0755 $(FLUTTER_ENGINE_BUILD_DIR)/icudtl.dat \
+		$(STAGING_DIR)/usr/share/flutter/$(FLUTTER_ENGINE_RUNTIME_MODE)/data/icudtl.dat
+endef
+
+define FLUTTER_ENGINE_INSTALL_TARGET_CMDS
+	$(foreach i,$(FLUTTER_ENGINE_INSTALL_FILES),
+		$(INSTALL) -D -m 0755 $(FLUTTER_ENGINE_BUILD_DIR)/so.unstripped/$(i) \
+			$(TARGET_DIR)/usr/lib/$(i); \
+	)
+	$(INSTALL) -D -m 0755 $(FLUTTER_ENGINE_BUILD_DIR)/icudtl.dat \
+		$(TARGET_DIR)/usr/share/flutter/$(FLUTTER_ENGINE_RUNTIME_MODE)/data/icudtl.dat
+endef
+
+$(eval $(generic-package))

package/flutter-engine/gen-tarball

@@ -0,0 +1,93 @@
+#!/usr/bin/env bash
+# Call gclient and generate a flutter-engine source tarball if one does not
+# already exist.
+set -eu
+
+DL_DIR=
+DOT_GCLIENT=
+JOBS=
+SCRATCH_DIR=
+TARBALL_DL_PATH=
+VERSION=
+TARBALL_NAME=
+
+term_bold="$(tput smso 2>/dev/null || true)"
+term_reset="$(tput rmso 2>/dev/null || true)"
+
+# Print status messages in the same style Buildroot prints.
+message() {
+    printf "%s>>> flutter-engine %s %s%s\n" "${term_bold}" "${VERSION}" "${1}" "${term_reset}"
+}
+
+parse_opts() {
+    local o O opts
+
+    o='d:j:s:t:v:'
+    O='dot-gclient:,jobs:,scratch-dir:,tarball-dl-path:,version:'
+    opts="$(getopt -o "${o}" -l "${O}" -- "${@}")"
+    eval set -- "${opts}"
+
+    while [ ${#} -gt 0 ]; do
+        case "${1}" in
+          (-d|--dot-gclient)        DOT_GCLIENT="${2}"; shift 2;;
+          (-j|--jobs)               JOBS="${2}"; shift 2;;
+          (-s|--scratch-dir)        SCRATCH_DIR="${2}"; shift 2;;
+          (-t|--tarball-dl-path)    DL_DIR=$(dirname "${2}"); TARBALL_DL_PATH="${2}"; shift 2;;
+          (-v|--version)            VERSION="${2}"; TARBALL_NAME=flutter-"${VERSION}".tar.gz; shift 2;;
+          (--)                      shift; break;;
+        esac
+    done
+}
+
+prepare() {
+    rm -rf "${SCRATCH_DIR}"
+    mkdir -p "${SCRATCH_DIR}"
+    pushd "${SCRATCH_DIR}" >/dev/null
+}
+
+copy_dot_gclient() {
+    sed "s%!FLUTTER_VERSION!%${VERSION}%g" "${DOT_GCLIENT}" >.gclient
+}
+
+run_gclient() {
+    message "Downloading"
+    gclient.py \
+        sync \
+        --delete_unversioned_trees \
+        --no-history \
+        --reset \
+        --shallow \
+        -j"${JOBS}"
+}
+
+gen_tarball() {
+    message "Generating tarball"
+    mkdir -p "${DL_DIR}"
+    # There are two issues with the flutter-engine buildsystem:
+    # - it expects empty directories created by gclient.py to be present; that
+    #   means we can't use the mk_tar_gz helper method from support/download/helpers,
+    #   becasue it does not include emnpty directories;
+    # - it insists on having a full git repositoy, with .git et al., which means
+    #   we can't generate a reproducible archive anyway.
+    # So we jsut create a plain tarball.
+    tar -C "${SCRATCH_DIR}"/src -czf "${TARBALL_NAME}" .
+    mv "${TARBALL_NAME}" "${TARBALL_DL_PATH}"
+}
+
+cleanup() {
+    popd >/dev/null
+    rm -rf "${SCRATCH_DIR}"
+}
+
+main() {
+    parse_opts "${@}"
+    if [[ ! -e "${TARBALL_DL_PATH}" ]]; then
+        prepare
+        copy_dot_gclient
+        run_gclient
+        gen_tarball
+        cleanup
+    fi
+}
+
+main "${@}"