restore buildMix and its bootstrapper (#122374)

* restore mixBuild

remove bootstrapper by going through ERL_LIBS
mix will use ERL_LIBS to find compiled dependencies

Co-authored-by: Zach <zach@hipcreativeinc.com>

2 files changed, 86 insertions, 0 deletions

diff --git a/pkgs/development/beam-modules/build-mix.nix b/pkgs/development/beam-modules/build-mix.nix
new file mode 100644
index 00000000000..7e19f19a093
--- /dev/null
+++ b/pkgs/development/beam-modules/build-mix.nix
@@ -0,0 +1,85 @@
+{ stdenv, writeText, elixir, erlang, hex, lib }:
+
+{ name
+, version
+, src
+, buildInputs ? [ ]
+, beamDeps ? [ ]
+, propagatedBuildInputs ? [ ]
+, postPatch ? ""
+, compilePorts ? false
+, meta ? { }
+, enableDebugInfo ? false
+, mixEnv ? "prod"
+, ...
+}@attrs:
+
+with lib;
+let
+  shell = drv: stdenv.mkDerivation {
+    name = "interactive-shell-${drv.name}";
+    buildInputs = [ drv ];
+  };
+
+  pkg = self: stdenv.mkDerivation (attrs // {
+    name = "${name}-${version}";
+    inherit version;
+    inherit src;
+
+    MIX_ENV = mixEnv;
+    MIX_DEBUG = if enableDebugInfo then 1 else 0;
+    HEX_OFFLINE = 1;
+
+    # stripping does not have any effect on beam files
+    dontStrip = true;
+
+    # add to ERL_LIBS so other modules can find at runtime.
+    # http://erlang.org/doc/man/code.html#code-path
+    # Mix also searches the code path when compiling with the --no-deps-check
+    # flag, which is why there is no complicated booterstrapper like the one
+    # used by buildRebar3.
+    setupHook = attrs.setupHook or
+      writeText "setupHook.sh" ''
+      addToSearchPath ERL_LIBS "$1/lib/erlang/lib"
+    '';
+
+    buildInputs = buildInputs ++ [ elixir hex ];
+    propagatedBuildInputs = propagatedBuildInputs ++ beamDeps;
+
+    buildPhase = attrs.buildPhase or ''
+      runHook preBuild
+      export HEX_HOME="$TEMPDIR/hex"
+      export MIX_HOME="$TEMPDIR/mix"
+      mix compile --no-deps-check
+      runHook postBuild
+    '';
+
+    installPhase = attrs.installPhase or ''
+      runHook preInstall
+
+      # This uses the install path convention established by nixpkgs maintainers
+      # for all beam packages. Changing this will break compatibility with other
+      # builder functions like buildRebar3 and buildErlangMk.
+      mkdir -p "$out/lib/erlang/lib/${name}-${version}"
+
+      # Some packages like db_connection will use _build/shared instead of
+      # honoring the $MIX_ENV variable.
+      for reldir in _build/{$MIX_ENV,shared}/lib/${name}/{src,ebin,priv,include} ; do
+        if test -d $reldir ; then
+          # Some builds produce symlinks (eg: phoenix priv dircetory). They must
+          # be followed with -H flag.
+          cp  -Hrt "$out/lib/erlang/lib/${name}-${version}" "$reldir"
+        fi
+      done
+
+      runHook postInstall
+    '';
+
+    passthru = {
+      packageName = name;
+      env = shell self;
+      inherit beamDeps;
+    };
+  });
+in
+fix pkg
diff --git a/pkgs/development/beam-modules/default.nix b/pkgs/development/beam-modules/default.nix
index f63ecd95083..3375fd61260 100644
--- a/pkgs/development/beam-modules/default.nix
+++ b/pkgs/development/beam-modules/default.nix
@@ -32,6 +32,7 @@ let
       buildRebar3 = callPackage ./build-rebar3.nix { };
       buildHex = callPackage ./build-hex.nix { };
       buildErlangMk = callPackage ./build-erlang-mk.nix { };
+      buildMix = callPackage ./build-mix.nix { };
       fetchMixDeps = callPackage ./fetch-mix-deps.nix { };
       mixRelease = callPackage ./mix-release.nix { };