Fix UndefinedFunctionError on custom allowlist modules

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Dev
 
+### Bug fixes
+
+- Fix `UndefinedFunctionError` when using external modules in a custom allowlist
+
 ## v0.3.3 (2023-08-13)
 
 ### Bug fixes

lib/dune/allowlist.ex

@@ -171,6 +171,16 @@ defmodule Dune.Allowlist do
     quote do
       unquote(def_spec(spec))
       unquote(def_fun_status(spec))
+
+      @on_load :ensure_alias_atoms
+
+      # Aliases like Foo.Bar are represented on the AST level as {:alias, _, [:Foo, :Bar]}
+      # We need to force the creation of these atoms, which might otherwise not be
+      # available when we parse due to atom encoding logic.
+      def ensure_alias_atoms do
+        # do nothing and returns :ok
+        Enum.each(unquote(alias_atoms(spec)), & &1)
+      end
     end
   end
 
@@ -236,4 +246,19 @@ defmodule Dune.Allowlist do
         :ok
     end
   end
+
+  defp alias_atoms(spec) do
+    spec.modules
+    |> Enum.flat_map(fn {mod, _} ->
+      try do
+        Module.split(mod)
+      rescue
+        ArgumentError ->
+          # "expected an Elixir module" error -> erlang module
+          []
+      end
+    end)
+    |> Enum.map(&String.to_atom/1)
+    |> Enum.uniq()
+  end
 end

lib/dune/parser/atom_encoder.ex

@@ -125,16 +125,9 @@ defmodule Dune.Parser.AtomEncoder do
     WithClauseError
   ]
 
-  # TODO add
-  @erlang_modules [:math]
-
-  @elixir_reprs @elixir_modules
+  @module_reprs @elixir_modules
                 |> Enum.flat_map(&Module.split/1)
-                |> Enum.map(&{&1, String.to_existing_atom(&1)})
-
-  @erlang_reprs Enum.map(@erlang_modules, &{Atom.to_string(&1), &1})
-
-  @module_reprs Map.new(@elixir_reprs ++ @erlang_reprs)
+                |> Map.new(&{&1, String.to_existing_atom(&1)})
 
   @spec load_atom_mapping(AtomMapping.t() | nil) :: :ok
   def load_atom_mapping(nil), do: :ok