Refactor the Docker image

Dockerfile

@@ -1,7 +1,3 @@
-# this is a pinned ubuntu:22.04 (newer versions have incomptible
-# library versions for souffle)
-FROM ubuntu@sha256:67211c14fa74f070d27cc59d69a7fa9aeff8e28ea118ef3babc295a0428a6d21
-
 ARG GID=1000
 ARG UID=1000
 
@@ -15,6 +11,12 @@ ARG GHCID_VERSION=0.8.9
 ARG GHC_TAGS_VERSION=1.9
 ARG POSTGRESQL_MIGRATION_VERSION=0.2.1.8
 
+# this is a pinned ubuntu:22.04 (newer versions have incomptible
+# library versions for souffle)
+FROM ubuntu@sha256:67211c14fa74f070d27cc59d69a7fa9aeff8e28ea118ef3babc295a0428a6d21 AS base
+ARG USER ${USER}
+ARG GID
+ARG UID
 # generate a working directory
 USER "root"
 ARG USER="local"
@@ -32,6 +34,7 @@ WORKDIR /flora-server
 RUN apt update && \
     apt install -y build-essential curl libffi-dev libffi8 libgmp-dev libgmp10 libncurses-dev libncurses5 libtinfo5 git libsodium-dev pkg-config
 
+FROM base AS ghcup
 # install dependencies (pg_config, postgresql-client, yarn)
 ENV BOOTSTRAP_HASKELL_NONINTERACTIVE="YES"
 ENV BOOTSTRAP_HASKELL_INSTALL_NO_STACK="YES"
@@ -52,8 +55,8 @@ RUN ghcup install hls $HLS_VERSION \
     && ghcup set ghc $GHC_VERSION \
     && ghcup install cabal $CABAL_VERSION
 
-USER ${USER}
 
+FROM base AS souffle
 # install soufflé
 USER "root"
 RUN wget --content-disposition https://github.com/souffle-lang/souffle/releases/download/2.2/x86_64-ubuntu-2004-souffle-2.2-Linux.deb
@@ -62,23 +65,38 @@ USER ${USER}
 
 RUN echo $PATH
 
-# install Haskell tooling (note that for cabal, it's probably better
-# to run `cabal update` as separate step, as cabal doesn't delete
-# package versions)
+FROM ghcup AS haskell-tools
+
+USER ${USER}
+
+ARG APPLY_REFACT_VERSION
+ARG CABAL_FMT_VERSION
+ARG CABAL_VERSION
+ARG FOURMOLU_VERSION
+ARG GHCID_VERSION
+ARG GHC_TAGS_VERSION
+ARG HLINT_VERSION
+ARG POSTGRESQL_MIGRATION_VERSION
+
 RUN cabal update
-RUN cabal install -j postgresql-migration-$POSTGRESQL_MIGRATION_VERSION
-RUN cabal install -j hlint-$HLINT_VERSION
 RUN cabal install -j apply-refact-$APPLY_REFACT_VERSION
-RUN cabal install -j fourmolu-$FOURMOLU_VERSION
 RUN cabal install -j cabal-fmt-$CABAL_FMT_VERSION
+RUN cabal install -j fourmolu-$FOURMOLU_VERSION
 RUN cabal install -j ghcid-$GHCID_VERSION
 RUN cabal install -j ghc-tags-$GHC_TAGS_VERSION
+RUN cabal install -j hlint-$HLINT_VERSION
+RUN cabal install -j postgresql-migration-$POSTGRESQL_MIGRATION_VERSION
 
+FROM base AS shell-config
 # configure the shell
+
+USER ${USER}
+
 RUN sh -c "$(curl -fsSL https://raw.github.com/ohmyzsh/ohmyzsh/master/tools/install.sh)"
 COPY --chown=${USER} scripts/shell-welcome.txt /etc/motd
 COPY --chown=${USER} scripts/.zshrc /home/$USER/.zshrc
 
+FROM ghcup AS server
 # build Haskell dependencies
 COPY --chown=${USER} cabal.project flora.cabal cabal.project.freeze ./
 RUN cabal build --only-dependencies -j