Create wrappers around nix / nix-build that divert the store to the n…

…etlify cache directory

Dockerfile

@@ -405,9 +405,10 @@ RUN mkdir -m 0755 /nix && chown buildbot /nix
 USER buildbot
 WORKDIR /tmp
 RUN curl -o install-nix https://nixos.org/nix/install && USER=buildbot sh ./install-nix && rm install-nix
+RUN mkdir -p /opt/buildhome/.nix/bin
 
-ENV PATH=/nix/var/nix/profiles/per-user/$USER/profile/bin:/nix/var/nix/profiles/per-user/$USER/profile/sbin:$PATH
-ENV NIX_PATH=/nix/var/nix/profiles/per-user/$USER/channels
+ENV PATH=/opt/buildhome/.nix/bin:$PATH
+ENV NIX_PATH=/nix/var/nix/profiles/per-user/buildbot/channels
 ENV NIX_SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt
 
 # Cleanup

run-build-functions.sh

@@ -202,7 +202,7 @@ install_dependencies() {
   fi
 
   if nvm install $NODE_VERSION
-  then 
+  then
     NODE_VERSION=$(nvm current)
     # no echo needed because nvm does that for us
     export NODE_VERSION=$NODE_VERSION
@@ -276,7 +276,7 @@ install_dependencies() {
       exit 1
     fi
   fi
-  
+
   if ! gem list -i "^bundler$" > /dev/null 2>&1
   then
     if ! gem install bundler
@@ -607,6 +607,23 @@ install_missing_commands() {
       export PATH=$(npm bin):$PATH
     fi
   fi
+
+  # Create wrappers around nix / nix-build that divert the store to the cache
+  # directory. This must be done at runtime and can not be baked into the
+  # docker image because it depends on NETLIFY_CACHE_DIR which is available
+  # only during execution.
+  #
+  # Furthermore, these commands must be provided to the user command as normal
+  # executables. I'd love to just make wrapper functions in the shell but anything
+  # that's defined in this file is *not* available to the user command.
+
+  echo '#!/bin/sh
+CMD=$1;shift;exec /nix/var/nix/profiles/per-user/buildbot/profile/bin/nix $CMD --store '$NETLIFY_CACHE_DIR' "$@"
+' > $HOME/.nix/bin/nix
+  echo '#!/bin/sh
+exec /nix/var/nix/profiles/per-user/buildbot/profile/bin/nix-build --store '$NETLIFY_CACHE_DIR' "$$@"
+' > $HOME/.nix/bin/nix-build
+  chmod +x $HOME/.nix/bin/nix $HOME/.nix/bin/nix-build
 }
 
 set_go_import_path() {