Avoid compile-time dependencies between parent and

polymorphic embedded schemas

Author: mathieuprog

CHANGELOG.md

@@ -4,6 +4,7 @@
 
   * Default value for polymorphic list of embeds is `[]` instead of `nil` (following `embeds_many/3`)
   * Support Phoenix HTML 4.0
+  * Avoid compile-time dependencies between parent and polymorphic embedded schemas
 
 ### Migration from 2.x to 3.x
 

lib/polymorphic_embed.ex

@@ -1,22 +1,71 @@
 defmodule PolymorphicEmbed do
   use Ecto.ParameterizedType
 
+  require Logger
+
   alias Ecto.Changeset
 
   defmacro polymorphic_embeds_one(field_name, opts) do
+    opts = Keyword.update!(opts, :types, &expand_alias(&1, __CALLER__))
+
     quote do
       field(unquote(field_name), PolymorphicEmbed, unquote(opts))
     end
   end
 
   defmacro polymorphic_embeds_many(field_name, opts) do
-    opts = Keyword.merge(opts, default: [])
+    opts =
+      opts
+      |> Keyword.put_new(:default, [])
+      |> Keyword.update!(:types, &expand_alias(&1, __CALLER__))
 
     quote do
       field(unquote(field_name), {:array, PolymorphicEmbed}, unquote(opts))
     end
   end
 
+  # Expand module aliases to avoid creating compile-time dependencies between the
+  # parent schema that uses `polymorphic_embeds_one` or `polymorphic_embeds_many`
+  # and the embedded schemas.
+  defp expand_alias(types, env) when is_list(types) do
+    Enum.map(types, fn
+      {type_name, type_opts} when is_list(type_opts) ->
+        {type_name, Keyword.update!(type_opts, :module, &do_expand_alias(&1, env))}
+
+      {type_name, module} ->
+        {type_name, do_expand_alias(module, env)}
+    end)
+  end
+
+  # If it's not a list or a map, it means it's being defined by a reference of some kind,
+  # possibly via module attribute like:
+  # @types [twilio: PolymorphicEmbed.Channel.TwilioSMSProvider]
+  # # ...
+  #   polymorphic_embeds_one(:fallback_provider, types: @types)
+  # which means we can't expand aliases
+  defp expand_alias(types, env) do
+    Logger.warning("""
+    Aliases could not be expanded for the given types in #{inspect(env.module)}.
+
+    This likely means the types are defined using a module attribute or another reference
+    that cannot be expanded at compile time. As a result, this may lead to unnecessary
+    compile-time dependencies, causing longer compilation times and unnecessary
+    re-compilation of modules (the parent defining the embedded types).
+
+    Ensure that the types are specified directly within the macro call to avoid these issues,
+    or refactor your code to eliminate references that cannot be expanded.
+    """)
+    types
+  end
+
+  defp do_expand_alias({:__aliases__, _, _} = ast, env) do
+    Macro.expand(ast, %{env | function: {:__schema__, 2}})
+  end
+
+  defp do_expand_alias(ast, _env) do
+    ast
+  end
+
   @impl true
   def type(_params), do: :map