ghcjs-boot fails with cabal: can't find source for GHC/Platform/Host

[minoki]

I'm trying to build ghcjs with the following Dockerfile:

FROM ubuntu:20.04
RUN apt-get update && apt-get install -y autoconf curl gcc git libgmp-dev libtinfo-dev make python3
RUN curl --proto '=https' --tlsv1.2 -sSf https://get-ghcup.haskell.org | env BOOTSTRAP_HASKELL_NONINTERACTIVE=1 BOOTSTRAP_HASKELL_MINIMAL=1 sh
ENV PATH=/root/.cabal/bin:/root/.ghcup/bin:$PATH
RUN ghcup install ghc 8.10.7 --set && \
    ghcup install cabal 3.6.2.0 && \
    cabal v2-update && \
    cabal v2-install --constraint "happy==1.19.*" --overwrite-policy=always alex happy
WORKDIR /root
RUN git clone --depth 1 https://github.com/emscripten-core/emsdk.git
WORKDIR /root/emsdk
RUN ./emsdk install latest && ./emsdk activate latest
WORKDIR /root
RUN git clone --depth 1 --branch ghc-8.10 --recurse-submodules --shallow-submodules https://github.com/ghcjs/ghcjs.git
WORKDIR /root/ghcjs
RUN utils/makePackages.sh
RUN cabal v2-install --overwrite-policy=always --install-method=copy --installdir=inplace/bin --disable-documentation

# emsdk_env.sh doesn't work with plain shell
RUN bash -c 'source /root/emsdk/emsdk_env.sh && inplace/bin/ghcjs-boot --no-prof --no-haddock -s lib/boot'

...but the last stage (ghcjs-boot) fails with the following error:

...
Registering library for parsec-3.1.14.0..
installing package ghc-boot
configuring package: ghc-boot
/root/ghcjs/lib/boot/pkg/ghc-boot$ /root/.ghcup/bin/cabal "v1-configure" "--global" "--ghcjs" "--builddir" "dist" "--with-compiler" "/root/ghcjs/inplace/bin/ghcjs" "--with-hc-pkg" "/root/ghcjs/inplace/bin/ghcjs-pkg" "--with-haddock" "/root/ghcjs/inplace/bin/haddock" "--with-gcc" "/root/ghcjs/inplace/lib/bin/emcc" "--prefix" "/root/ghcjs/inplace" "--configure-option" "--host=js-unknown-ghcjs" "--ghcjs-options=-fwrite-ide-info" "--enable-debug-info" "--disable-library-stripping" "--disable-executable-stripping" "-fghci" "--disable-profiling" "--enable-shared"
Warning: Unknown/unsupported 'ghc' version detected (Cabal 3.6.2.0 supports
'ghc' version < 8.8): /root/ghcjs/inplace/bin/ghcjs is based on GHC version
8.10.7
Warning: ghc-boot.cabal:25:23: Packages with 'cabal-version: 1.12' or later
should specify a specific version of the Cabal spec of the form
'cabal-version: x.y'. Use 'cabal-version: 1.22'.
Resolving dependencies...
Warning: ghc-boot.cabal:25:23: Packages with 'cabal-version: 1.12' or later
should specify a specific version of the Cabal spec of the form
'cabal-version: x.y'. Use 'cabal-version: 1.22'.
Configuring ghc-boot-8.10.7...
/root/ghcjs/lib/boot/pkg/ghc-boot$ /root/.ghcup/bin/cabal "v1-build"
Warning: ghc-boot.cabal:25:23: Packages with 'cabal-version: 1.12' or later
should specify a specific version of the Cabal spec of the form
'cabal-version: x.y'. Use 'cabal-version: 1.22'.
Preprocessing library for ghc-boot-8.10.7..
cabal: can't find source for GHC/Platform/Host in ., dist/build/autogen,
dist/build/global-autogen

fatal: program /root/.ghcup/bin/cabal returned a nonzero exit code