fix: don't raise when an operator on two literals yields a struct (ash-project#2847)

Author: matt-beanland

lib/ash/filter/filter.ex

@@ -4086,10 +4086,13 @@ defmodule Ash.Filter do
     end
   end
 
-  defp maybe_operator_expression(operator, context) when is_struct(operator) do
+  # Over two literals the operator is evaluated on construction, so the result arrives here.
+  defp maybe_operator_expression(
+         %{__operator__?: true, left: left, right: right} = operator,
+         context
+       ) do
     case Ash.Query.Operator.operator_expression(operator) do
       {:ok, expr_module} ->
-        %{left: left, right: right} = operator
         arguments = [left, right]
         resource = context[:resource]
 

test/expr_test.exs

@@ -162,6 +162,36 @@ defmodule Ash.Test.ExprTest do
     end
   end
 
+  describe "operators over two literals" do
+    test "a result that is not a struct" do
+      assert eval!(expr(^1 + ^2)) == 3
+    end
+
+    test "a decimal result" do
+      assert eval!(expr(^Decimal.new(1) + ^Decimal.new(2))) == Decimal.new(3)
+    end
+
+    test "a datetime result" do
+      now = DateTime.utc_now()
+      duration = Duration.new!(day: 7)
+
+      assert eval!(expr(^now + ^duration)) == DateTime.shift(now, duration)
+    end
+
+    test "a date result" do
+      today = Date.utc_today()
+      duration = Duration.new!(day: 7)
+
+      assert eval!(expr(^today + ^duration)) == Date.shift(today, duration)
+    end
+
+    test "a duration result" do
+      duration = Duration.new!(day: 7)
+
+      assert eval!(expr(^duration + ^duration)) == Duration.add(duration, duration)
+    end
+  end
+
   describe "rem expressions" do
     test "evaluates" do
       expr = expr(rem(1, 2) == 0)