From a7fb18c80422580b4d305fbe90a4b6508bf91b2a Mon Sep 17 00:00:00 2001
From: superherointj <5861043+superherointj@users.noreply.github.com>
Date: Mon, 13 Feb 2023 16:57:36 -0300
Subject: [PATCH] beam/fetchMixDeps: disable --only flag when mixEnv is empty

* mixEnv being empty will include all dependencies.
---
 doc/languages-frameworks/beam.section.md         | 1 +
 pkgs/development/beam-modules/fetch-mix-deps.nix | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/doc/languages-frameworks/beam.section.md b/doc/languages-frameworks/beam.section.md
index 6b3a369c291f..707da43e9dd7 100644
--- a/doc/languages-frameworks/beam.section.md
+++ b/doc/languages-frameworks/beam.section.md
@@ -171,6 +171,7 @@ let
     inherit src version;
     # nix will complain and tell you the right value to replace this with
     hash = lib.fakeHash;
+    mixEnv = ""; # default is "prod", when empty includes all dependencies, such as "dev", "test".
     # if you have build time environment variables add them here
     MY_ENV_VAR="my_value";
   };
diff --git a/pkgs/development/beam-modules/fetch-mix-deps.nix b/pkgs/development/beam-modules/fetch-mix-deps.nix
index ac6d5f3c8b92..2bba3a93c294 100644
--- a/pkgs/development/beam-modules/fetch-mix-deps.nix
+++ b/pkgs/development/beam-modules/fetch-mix-deps.nix
@@ -45,7 +45,7 @@ stdenvNoCC.mkDerivation (attrs // {
 
   installPhase = attrs.installPhase or ''
     runHook preInstall
-    mix deps.get --only ${mixEnv}
+    mix deps.get ''${mixEnv:+--only $mixEnv}
     find "$TEMPDIR/deps" -path '*/.git/*' -a ! -name HEAD -exec rm -rf {} +
     cp -r --no-preserve=mode,ownership,timestamps $TEMPDIR/deps $out
     runHook postInstall