fix: support passing a forbidden error to policies per the docs

fixes #1443

lib/ash/error/forbidden/policy.ex

@@ -70,6 +70,12 @@ defmodule Ash.Error.Forbidden.Policy do
 
   - `:help_text?`: Defaults to true. Displays help text at the top of the policy breakdown.
   """
+  def report(%Ash.Error.Forbidden{errors: errors}) do
+    errors
+    |> Enum.filter(&(&1.__struct__ == __MODULE__))
+    |> Enum.map_join("\n\n", &report/1)
+  end
+
   def report(error, opts \\ []) do
     error
     |> get_errors()

test/policy/simple_test.exs

@@ -190,6 +190,19 @@ defmodule Ash.Test.Policy.SimpleTest do
                  end
   end
 
+  test "breakdowns can be shown for all policy errors in a forbidden error" do
+    res =
+      assert_raise Ash.Error.Forbidden,
+                   ~r/No policy conditions applied to this request/,
+                   fn ->
+                     ResourceWithAPolicyThatDoesntApply
+                     |> Ash.read!()
+                   end
+
+    assert Ash.Error.Forbidden.Policy.report(res) =~
+             ~r/No policy conditions applied to this request/
+  end
+
   test "an impossible create policy shows the correct error message" do
     assert_raise Ash.Error.Forbidden, ~r/Cannot use a filter to authorize a create/, fn ->
       ResourceWithAnImpossibleCreatePolicy