Add "compilePorts" enabling rebar3 "pc" plugin

If compilePorts is enabled plugin "pc" is added to the rebar.config
during postPatch. This makes rebar3 compile download the plugin, hence
added TODO.

pkgs/development/erlang-modules/build-hex.nix

@@ -4,6 +4,7 @@
 , hexPkg ? name
 , buildInputs ? [], erlangDeps ? []
 , postPatch ? ""
+, compilePorts ? false
 , ... }@attrs:
 
 with stdenv.lib;
@@ -18,6 +19,16 @@ stdenv.mkDerivation (attrs // {
     if [ -e "src/${name}.app.src" ]; then
       sed -i -e 's/{ *vsn *,[^}]*}/{vsn, "${version}"}/' "src/${name}.app.src"
     fi
+
+    # TODO: figure out how to provide 'pc' plugin hermetically
+    ${if compilePorts then ''
+    echo "{plugins, [pc]}.
+    {provider_hooks,
+    [{post,
+     [{compile, {pc, compile}},
+      {clean, {pc, clean}}]}]}." >> rebar.config
+    '' else ''''}
+
     ${postPatch}
   '';
 
@@ -43,6 +54,8 @@ stdenv.mkDerivation (attrs // {
     runHook postConfigure
   '';
 
+  # TODO: figure out how to provide rebar3 a static registry snapshot to make
+  # this hermetic
   buildPhase = ''
     runHook preBuild
     HOME=. rebar3 update

pkgs/development/erlang-modules/default.nix

@@ -7,6 +7,7 @@ let
     buildErlang = callPackage ./build-erlang.nix {};
     buildHex = callPackage ./build-hex.nix {};
 
+    esqlite = callPackage ./hex/esqlite.nix {};
     goldrush = callPackage ./hex/goldrush.nix {};
     ibrowse = callPackage ./hex/ibrowse.nix {};
     jiffy = callPackage ./hex/jiffy.nix {};

pkgs/development/erlang-modules/hex/esqlite.nix

@@ -0,0 +1,8 @@
+{ buildHex }:
+
+buildHex {
+  name = "esqlite";
+  version = "0.2.1";
+  sha256 = "1296fn1lz4lz4zqzn4dwc3flgkh0i6n4sydg501faabfbv8d3wkr";
+  compilePorts = true;
+}