mix: add build mix and mix-release configure-hook

pkgs/development/beam-modules/build-mix.nix

@@ -42,6 +42,14 @@ let
     nativeBuildInputs = nativeBuildInputs ++ [ elixir hex ];
     propagatedBuildInputs = propagatedBuildInputs ++ beamDeps;
 
+    configurePhase = attrs.configurePhase or ''
+      runHook preConfigure
+
+      ${./mix-configure-hook.sh}
+
+      runHook postConfigure
+    '';
+
     buildPhase = attrs.buildPhase or ''
       runHook preBuild
       export HEX_HOME="$TEMPDIR/hex"
@@ -83,3 +91,4 @@ let
   });
 in
 fix pkg
+

pkgs/development/beam-modules/mix-configure-hook.sh

@@ -0,0 +1,18 @@
+# shellcheck shell=bash
+# this hook will symlink all dependencies found in ERL_LIBS
+# since Elixir 1.12.2 elixir does not look into ERL_LIBS for
+# elixir depencencies anymore, so those have to be symlinked to the _build directory
+mkdir -p _build/"$MIX_ENV"/lib
+while read -r -d ':' lib; do
+    for dir in "$lib"/*; do
+    # Strip version number for directory name if it exists, so naming of
+    # all libs matches what mix's expectation.
+    dest=$(basename "$dir" | cut -d '-' -f1)
+    build_dir="_build/$MIX_ENV/lib/$dest"
+    ((MIX_DEBUG == 1)) && echo "Linking $dir to $build_dir"
+    # Symlink libs to _build so that mix can find them when compiling.
+    # This is what allows mix to compile the package without searching
+    # for dependencies over the network.
+    ln -s "$dir" "$build_dir"
+    done
+done <<< "$ERL_LIBS:"

pkgs/development/beam-modules/mix-release.nix

@@ -58,20 +58,7 @@ stdenv.mkDerivation (overridable // {
   configurePhase = attrs.configurePhase or ''
     runHook preConfigure
 
-    mkdir -p _build/$MIX_ENV/lib
-    while read -d ':' lib; do
-      for dir in $lib/*; do
-        # Strip version number for directory name if it exists, so naming of
-        # all libs matches what mix's expectation.
-        dest=$(basename $dir | cut -d '-' -f1)
-        echo "Linking $dir to _build/$MIX_ENV/lib/$dest"
-        # Symlink libs to _build so that mix can find them when compiling.
-        # This is what allows mix to compile the package without searching
-        # for dependencies over the network.
-        ln -s $dir _build/$MIX_ENV/lib/$dest
-      done
-    done <<< "$ERL_LIBS:"
-
+    ${./mix-configure-hook.sh}
     # this is needed for projects that have a specific compile step
     # the dependency needs to be compiled in order for the task
     # to be available