Make compatible with new GHC JS backend

[sevanspowell]

• We need to make a few changes to compile cborg with the new GHC Javascript backend.
• Tested with GHC 9.8.2.

[dcoutts]

Is there any way we can add GHCJS to the CI?

[sevanspowell]

Good question, I will have a look! 👍

[sevanspowell]

It seems using the new GHC Javascript backend is not yet possible using haskell-ci (which is used to generate the CI script in this repo), see haskell-CI/haskell-ci#723. So I'll have to take a look at submitting a PR against haskell-ci.

[sevanspowell]

I am attempting to use ghcup to build the javascript backend, but unfortunately the instructions in the user guide don't work (https://www.haskell.org/ghcup/guide/#ghc-js-cross-bindists-experimental). So far I've had limited success with:

docker run -it buildpack-deps:bionic bash
export VERSION="3.1.57"
git clone https://github.com/emscripten-core/emsdk.git
cd emsdk
./emsdk install "$VERSION"
./emsdk activate "$VERSION"
source ./emsdk_env.sh

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.7/install.sh | bash
nvm install 16.20.0
vi .emscripten > "NODE_JS = '/root/.nvm/versions/node/v16.20.0/bin/node'"

emconfigure ghcup install ghc 9.10.1 --set javascript-unknown-ghcjs

Failing with an issue regarding word size:

[ ghc-configure ] checking size of void *... 4
[ ghc-configure ] configure: error: This binary distribution produces binaries for a target with
[ ghc-configure ]                   word size of 8, but your target toolchain produces binaries
[ ghc-configure ]                   with a word size of 4. Are you sure your toolchain
[ ghc-configure ]                   targets the intended target platform of this compiler

I'll get back to this when I can.

[sevanspowell]

Had success building with ghcup!

docker run -it buildpack-deps:noble bash
apt-get update
apt-get install -y --no-install-recommends gnupg ca-certificates dirmngr curl git software-properties-common libtinfo5
mkdir -p "$HOME/.ghcup/bin"
curl -sL https://downloads.haskell.org/ghcup/0.1.22.0/x86_64-linux-ghcup-0.1.22.0 > "$HOME/.ghcup/bin/ghcup"
chmod a+x "$HOME/.ghcup/bin/ghcup"
export PATH="$HOME/.ghcup/bin":"${PATH}"

export EM_VERSION="3.1.57"
git clone https://github.com/emscripten-core/emsdk.git
cd emsdk
./emsdk install "$EM_VERSION"
./emsdk activate "$EM_VERSION"
source "/emsdk/emsdk_env.sh"

ghcup config add-release-channel https://raw.githubusercontent.com/haskell/ghcup-metadata/develop/ghcup-cross-0.0.8.yaml
emconfigure ghcup install ghc --set javascript-unknown-ghcjs-9.10.0.20240413
# emconfigure ghcup install ghc --set javascript-unknown-ghcjs-9.6.2

echo 'main = putStrLn "hello world"' > hello.hs
javascript-unknown-ghcjs-ghc -fforce-recomp hello.hs
./hello

I needed to:

• Set the release channel: ghcup config add-release-channel https://raw.githubusercontent.com/haskell/ghcup-metadata/develop/ghcup-cross-0.0.8.yaml
• Upgrade to Ubuntu Noble, in order to get the newer version of GLIBC.

So it is possible to build with ghcup, so it should be possible to submit a PR to haskell-ci to get GHCJS working with certain versions of GHC.