Modifications to merge logic (#9)

lib/splode.ex

@@ -57,6 +57,8 @@ defmodule Splode do
                          "must supply the `unknown_error` option, pointing at a splode error to use in situations where we cannot convert an error."
                        )
 
+      @merge_with List.wrap(opts[:merge_with])
+
       if Enum.empty?(opts[:error_classes]) do
         raise ArgumentError,
               "must supply at least one error class to `use Splode`, via `use Splode, error_classes: [class: ModuleForClass]`"
@@ -180,19 +182,27 @@ defmodule Splode do
           if Keyword.keyword?(values) && values != [] do
             [to_error(values, Keyword.delete(opts, :bread_crumbs))]
           else
-            Enum.map(values, &to_error(&1, Keyword.delete(opts, :bread_crumbs)))
+            values
+            |> flatten_preserving_keywords()
+            |> Enum.map(fn error ->
+              if Enum.any?([__MODULE__ | @merge_with], &splode_error?(error, &1)) do
+                error
+              else
+                to_error(error, Keyword.delete(opts, :bread_crumbs))
+              end
+            end)
           end
 
         if Enum.count_until(errors, 2) == 1 &&
-             Enum.at(errors, 0).class == :special do
+             (Enum.at(errors, 0).class == :special || Enum.at(errors, 0).__struct__.error_class?()) do
           List.first(errors)
         else
-          values
-          |> flatten_preserving_keywords()
+          errors
+          |> flatten_errors()
           |> Enum.uniq_by(&clear_stacktraces/1)
           |> Enum.map(fn value ->
-            if splode_error?(value, __MODULE__) do
-              Map.put(value, :splode, __MODULE__)
+            if Enum.any?([__MODULE__ | @merge_with], &splode_error?(value, &1)) do
+              Map.put(value, :splode, value.splode || __MODULE__)
             else
               exception_opts =
                 if opts[:stacktrace] do
@@ -219,16 +229,17 @@ defmodule Splode do
       end
 
       defp choose_error(errors) do
-        errors = Enum.map(errors, &to_error/1)
-
         [error | other_errors] =
           Enum.sort_by(errors, fn error ->
             # the second element here sorts errors that are already parent errors
-            {Map.get(@error_class_indices, error.class),
+            {Map.get(@error_class_indices, error.class) ||
+               Map.get(@error_class_indices, :unknown),
              @error_classes[error.class] != error.__struct__}
           end)
 
-        parent_error_module = @error_classes[error.class]
+        parent_error_module =
+          @error_classes[error.class] || Keyword.get(@error_classes, :unknown) ||
+            Splode.Error.Unknown
 
         if parent_error_module == error.__struct__ do
           %{error | errors: (error.errors || []) ++ other_errors}
@@ -271,16 +282,15 @@ defmodule Splode do
 
       def to_error(other, opts) do
         cond do
-          splode_error?(other, __MODULE__) ->
+          Enum.any?([__MODULE__ | @merge_with], &splode_error?(other, &1)) ->
             other
-            |> Map.put(:splode, __MODULE__)
+            |> Map.put(:splode, other.splode || __MODULE__)
             |> add_stacktrace(opts[:stacktrace])
             |> accumulate_bread_crumbs(opts[:bread_crumbs])
 
           is_exception(other) ->
             [error: Exception.format(:error, other), splode: __MODULE__]
             |> @unknown_error.exception()
-            |> Map.put(:stacktrace, nil)
             |> add_stacktrace(opts[:stacktrace])
             |> accumulate_bread_crumbs(opts[:bread_crumbs])
 
@@ -293,6 +303,22 @@ defmodule Splode do
         end
       end
 
+      defp flatten_errors(errors) do
+        errors
+        |> Enum.flat_map(&List.wrap/1)
+        |> Enum.flat_map(fn error ->
+          if Enum.any?([__MODULE__ | @merge_with], &splode_error?(error, &1)) do
+            if error.__struct__.error_class?() do
+              flatten_errors(error.errors)
+            else
+              [error]
+            end
+          else
+            [error]
+          end
+        end)
+      end
+
       defp flatten_preserving_keywords(list) do
         if Keyword.keyword?(list) do
           [list]

test/splode_test.exs

@@ -13,6 +13,11 @@ defmodule SplodeTest do
     use Splode.ErrorClass, class: :sw
   end
 
+  defmodule ContainerErrorClass do
+    @moduledoc false
+    use Splode.ErrorClass, class: :ui
+  end
+
   # Errors
 
   defmodule CpuError do
@@ -45,6 +50,18 @@ defmodule SplodeTest do
     def message(err), do: err |> inspect()
   end
 
+  defmodule ExampleContainerError do
+    @moduledoc false
+    use Splode.Error, fields: [:description], class: :ui
+    def message(err), do: err |> inspect()
+  end
+
+  defmodule ContainerUnknownError do
+    @moduledoc false
+    use Splode.Error, fields: [:error], class: :unknown
+    def message(err), do: err |> inspect()
+  end
+
   defmodule SystemError do
     @moduledoc false
     use Splode,
@@ -55,6 +72,28 @@ defmodule SplodeTest do
       unknown_error: UnknownError
   end
 
+  defmodule ContainerError do
+    @moduledoc false
+    use Splode,
+      error_classes: [
+        interaction: ContainerErrorClass,
+        hw: HwError,
+        sw: SwError
+      ],
+      unknown_error: ContainerUnknownError,
+      merge_with: [SystemError]
+  end
+
+  defmodule ContainerWithoutMergeWith do
+    @moduledoc false
+    use Splode,
+      error_classes: [
+        interaction: ContainerErrorClass
+      ],
+      unknown_error: ContainerUnknownError,
+      merge_with: []
+  end
+
   test "splode_error?" do
     refute SystemError.splode_error?(:error)
     refute SystemError.splode_error?(%{})
@@ -83,8 +122,15 @@ defmodule SplodeTest do
       ram = RamError.exception() |> SystemError.to_error()
       div = DivByZeroException.exception() |> SystemError.to_error()
       null = NullReferenceException.exception() |> SystemError.to_error()
-
-      %{cpu: cpu, ram: ram, div: div, null: null}
+      example_container_error = ExampleContainerError.exception() |> ContainerError.to_error()
+
+      %{
+        cpu: cpu,
+        ram: ram,
+        div: div,
+        null: null,
+        example_container_error: example_container_error
+      }
     end
 
     test "wraps errors in error class with same class", %{
@@ -123,6 +169,31 @@ defmodule SplodeTest do
 
       assert error == error |> SystemError.to_class()
     end
+
+    test "to_error flattens nested errors when included in merge_with", %{
+      cpu: cpu,
+      ram: ram,
+      example_container_error: example_container_error
+    } do
+      hw_error = [cpu, ram] |> SystemError.to_class()
+
+      interaction_error = ContainerError.to_class([hw_error, example_container_error])
+
+      assert %{errors: [^cpu, ^ram, ^example_container_error]} = interaction_error
+    end
+
+    test "to_error doesn't flatten nested errors when not included in merge_with", %{
+      cpu: cpu,
+      ram: ram,
+      example_container_error: example_container_error
+    } do
+      hw_error = [cpu, ram] |> SystemError.to_class()
+
+      interaction_error = ContainerWithoutMergeWith.to_class([hw_error, example_container_error])
+
+      assert %{errors: [%SplodeTest.ContainerUnknownError{}, %SplodeTest.ContainerUnknownError{}]} =
+               interaction_error
+    end
   end
 
   test "to_error" do