Update with tips from hasufell

Author: AlistairB

8.10/ghcup/Dockerfile

@@ -2,6 +2,7 @@ FROM debian:buster AS builder
 
 ENV LANG C.UTF-8
 
+# prereqs for ghcup + installing ghc, cabal + stack
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
         ca-certificates \
@@ -16,24 +17,41 @@ RUN apt-get update && \
         curl && \
     rm -rf /var/lib/apt/lists/*
 
+# install ghcup
 ARG GHCUP_VERSION=0.1.16.2
+RUN curl --proto '=https' --tlsv1.2 -sSf https://downloads.haskell.org/~ghcup/$GHCUP_VERSION/x86_64-linux-ghcup-$GHCUP_VERSION > /usr/bin/ghcup && \
+    chmod +x /usr/bin/ghcup
 
-RUN curl -fSL https://downloads.haskell.org/~ghcup/$GHCUP_VERSION/x86_64-linux-ghcup-$GHCUP_VERSION -o ghcup && \
-    chmod +x ghcup
-
+# install cabal
 ARG CABAL_VERSION=3.4.0.0
+RUN ghcup install cabal -i /usr/local/bin $CABAL_VERSION
 
-RUN ./ghcup install cabal $CABAL_VERSION && \
-    ./ghcup set cabal $CABAL_VERSION
+# install stack
+ARG STACK_VERSION=2.7.3
+RUN ghcup install stack -i /usr/local/bin $STACK_VERSION
 
+# install GHC into /opt/ghc
 ARG GHC_VERSION=8.10.6
+RUN ghcup install ghc -i /opt/ghc $GHC_VERSION
 
-RUN ./ghcup install ghc $GHC_VERSION && \
-    ./ghcup set ghc $GHC_VERSION
+FROM debian:buster
 
-ARG STACK_VERSION=2.7.3
+ENV LANG C.UTF-8
+
+# prereqs just for using ghc, cabal + stack
+# more would be added, main point is it will be slightly different
+# than the builder deps
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        libgmp-dev \
+        libgmp10 \
+        build-essential && \
+    rm -rf /var/lib/apt/lists/*
 
-RUN ./ghcup install stack $STACK_VERSION && \
-    ./ghcup set stack $STACK_VERSION
+COPY --from=builder /usr/local/bin /usr/local/bin
+COPY --from=builder /opt/ghc /opt/ghc
 
-RUN cp -H /root/.ghcup/bin/* /usr/local/bin
+# Adjust PATH
+RUN echo 'export PATH="/opt/ghc/bin:$PATH"' >> /etc/profile.d/ghcup_path.sh && \
+	chmod +x /etc/profile.d/ghcup_path.sh
+ENV PATH="/opt/ghc/bin:$PATH"