Move compilation into entrypoint; Call entrypoint on build

Dockerfile

@@ -70,8 +70,7 @@ RUN \
 
 # Precompile
 RUN \
-       mix deps.get \
-    && mix compile
+       NO_CONFIG=1 COMPILE_ONLY=1 /entrypoint.sh
 
 # Prepare runtime config
 RUN \
@@ -80,5 +79,3 @@ RUN \
 
 # Insert overrides
 COPY --chown=pleroma:pleroma ./custom.d /home/pleroma/pleroma
-
-# Recompiles at runtime if custom.d contained elixir code.

entrypoint.sh

@@ -3,15 +3,20 @@
 set -e
 set -x
 
-# Generate a config file
+if [[ -z "$NO_CONFIG" ]]; then
     ruby /conf/parser.rb /conf/config.yml > config/runtime-config.exs
+fi
 
-# Recompile if needed
-if [[ ! -z "$RECOMPILE" ]]; then
+if [[ -n "$COMPILE_ONLY" ]]; then
     mix deps.get
     mix compile
+    exit 0
 fi
 
+# Assume that dependencies are compiled and ready to go.
+# Remove this assumption when https://github.com/erlang/rebar3/issues/1627 is fixed.
+mix compile
+
 # Migrate db
 mix ecto.create
 mix ecto.migrate