The prebuilt version must match the sources in //third_party/dart exactly. The
update.py script downloads a package for the build host that matches the current Dart revision according to
jiri project. It's run automatically by the Jiri manifest but can also be run by hand at any time. Run it with
--help for details.
If there is no prebuilt for your build host, then you‘ll have to supply your own. It’s a normal
dart-sdk built for the build host, but it also needs
bin/gen_shapshot_product.OS-CPU. These run on the build host but target a corresponding Dart VM built for
OS-CPU. The Fuchsia GN build will run those for both
fuchsia-arm64). This all must be built from Dart sources that exactly match the version in //third_dart/dart that will be built in the Fuchsia GN build.
The GN build argument
prebuilt_dart_sdk sets the directory where GN will look for Dart. Its default is the
$host_os-$host_cpu subdirectory here, where the
update.py script unpacks it by default. To use a different build of Dart, just set that in