misc fixes for error traversing function

config/dev.exs

@@ -0,0 +1 @@
+# dummy comment to suppress failing tests

lib/polymorphic_embed.ex

@@ -1,6 +1,8 @@
 defmodule PolymorphicEmbed do
   use Ecto.ParameterizedType
 
+  @relations [:embed, :assoc]
+
   defmacro polymorphic_embeds_one(field_name, opts) do
     quote do
       field(unquote(field_name), PolymorphicEmbed, unquote(opts))
@@ -418,10 +420,14 @@ defmodule PolymorphicEmbed do
   defp raise_cannot_infer_type_from_data(data),
     do: raise("could not infer polymorphic embed from data #{inspect(data)}")
 
-  def traverse_errors(%Ecto.Changeset{changes: changes, types: types} = changeset, msg_func)
+  def traverse_errors(
+        %Ecto.Changeset{changes: changes, types: types, errors: errors} = changeset,
+        msg_func
+      )
       when is_function(msg_func, 1) or is_function(msg_func, 3) do
-    changeset
-    |> Ecto.Changeset.traverse_errors(msg_func)
+    errors
+    |> Enum.reverse()
+    |> merge_keyword_keys(msg_func, changeset)
     |> merge_polymorphic_keys(changes, types, msg_func)
   end
 
@@ -433,6 +439,20 @@ defmodule PolymorphicEmbed do
     %{}
   end
 
+  defp merge_keyword_keys(keyword_list, msg_func, _) when is_function(msg_func, 1) do
+    Enum.reduce(keyword_list, %{}, fn {key, val}, acc ->
+      val = msg_func.(val)
+      Map.update(acc, key, [val], &[val | &1])
+    end)
+  end
+
+  defp merge_keyword_keys(keyword_list, msg_func, changeset) when is_function(msg_func, 3) do
+    Enum.reduce(keyword_list, %{}, fn {key, val}, acc ->
+      val = msg_func.(changeset, key, val)
+      Map.update(acc, key, [val], &[val | &1])
+    end)
+  end
+
   defp merge_polymorphic_keys(map, changes, types, msg_func) do
     Enum.reduce(types, map, fn
       {field, {:parameterized, PolymorphicEmbed, _opts}}, acc ->
@@ -445,6 +465,11 @@ defmodule PolymorphicEmbed do
           acc
         end
 
+      {field, {:parameterized, parameterized_type, _opts}}, acc ->
+        if function_exported?(parameterized_type, :traverse_errors, 4),
+          do: parameterized_type.traverse_errors(field, changes, msg_func, acc),
+          else: acc
+
       {field, {:array, {:parameterized, PolymorphicEmbed, _opts}}}, acc ->
         if changesets = Map.get(changes, field) do
           {errors, all_empty?} =
@@ -461,6 +486,42 @@ defmodule PolymorphicEmbed do
           acc
         end
 
+      # `Ecto.Schema.embeds_one()` field(s) inside of ecto-based schemas gets translated
+      # to the changeset type {:embed, %Ecto.Embedded{cardinality: :one, field: field}}
+      # and `Ecto.Schema.belongs_to()` get translated to
+      # {:assoc, %Ecto.Association.Has{cardinality: :one, field: field}}
+      # where the :cardinality atom can be one of: `:one` or `:many`, hence can be
+      # pattern-matched in order to distinguish between `one` and `many` cardinality
+      {field, {tag, %{cardinality: :one, field: field}}}, acc when tag in @relations ->
+        if changeset = Map.get(changes, field) do
+          case traverse_errors(changeset, msg_func) do
+            errors when errors == %{} -> acc
+            errors -> Map.put(acc, field, errors)
+          end
+        else
+          acc
+        end
+
+      # `Ecto.Schema.embeds_many()` field(s) inside of ecto-based schemas gets translated
+      # to the changeset type {:embed, %Ecto.Embedded{cardinality: :many, field: field}}
+      # and `Ecto.Schema.has_many()` get translated to
+      # {:assoc, %Ecto.Association.Has{cardinality: :many, field: field}}
+      # where the :cardinality atom can be one of: `:one` or `:many`, hence can be
+      # pattern-matched in order to distinguish between `one` and `many` cardinality
+      {field, {tag, %{cardinality: :many, field: field}}}, acc when tag in @relations ->
+        multiple_changesets = Map.get(changes, field)
+
+        if not is_nil(multiple_changesets) and is_list(multiple_changesets) do
+          Enum.reduce(multiple_changesets, acc, fn changeset, acc ->
+            case traverse_errors(changeset, msg_func) do
+              errors when errors == %{} -> acc
+              errors -> Map.update(acc, field, [errors], &[errors | &1])
+            end
+          end)
+        else
+          acc
+        end
+
       {_, _}, acc ->
         acc
     end)

mix.exs

@@ -48,7 +48,7 @@ defmodule PolymorphicEmbed.MixProject do
   defp deps do
     [
       {:ecto, "~> 3.9"},
-      {:jason, "~> 1.4"},
+      {:jason, "~> 1.2"},
       {:phoenix_html, "~> 2.14 or ~> 3.2", optional: true},
       {:ex_doc, "~> 0.28", only: :dev},
       {:ecto_sql, "~> 3.9", only: :test},