Expand macros in window frames (#4730)

Author: dannote

lib/ecto/query/builder/windows.ex

@@ -72,8 +72,21 @@ defmodule Ecto.Query.Builder.Windows do
   defp escape_frame({:fragment, _, _} = fragment, params_acc, vars, env) do
     Builder.escape(fragment, :any, params_acc, vars, env)
   end
-  defp escape_frame(other, _, _, _) do
-    Builder.error!("expected a dynamic or fragment in `:frame`, got: `#{inspect other}`")
+
+  defp escape_frame(other, params_acc, vars, env) do
+    macro_env =
+      case env do
+        {env, _} -> env
+        env -> env
+      end
+
+    case Macro.expand_once(other, macro_env) do
+      ^other ->
+        Builder.error!("expected a dynamic or fragment in `:frame`, got: `#{inspect other}`")
+
+      expanded ->
+        escape_frame(expanded, params_acc, vars, env)
+    end
   end
 
   defp error!(other) do

test/ecto/query/builder/windows_test.exs

@@ -6,6 +6,18 @@ defmodule Ecto.Query.Builder.WindowsTest do
 
   import Ecto.Query
 
+  defmacrop rows_between_preceding(count) do
+    quote do
+      fragment(unquote("ROWS BETWEEN #{count} PRECEDING AND CURRENT ROW"))
+    end
+  end
+
+  defmacro invalid_frame do
+    quote do
+      [rows: -3, exclude: :current]
+    end
+  end
+
   describe "escape" do
     test "handles expressions and params" do
       assert {Macro.escape(quote(do: [partition_by: [&0.y()]])), [], {[], %{}}} ==
@@ -63,6 +75,26 @@ defmodule Ecto.Query.Builder.WindowsTest do
       query = "q" |> windows([p], w: [frame: fragment("FOOBAR")])
       assert query.windows[:w].expr[:frame] == {:fragment, [], [raw: "FOOBAR"]}
     end
+
+    test "defines frame with macro that expands to fragment" do
+      query = "q" |> windows([p], w: [frame: rows_between_preceding(6)])
+
+      assert query.windows[:w].expr[:frame] ==
+               {:fragment, [], [raw: "ROWS BETWEEN 6 PRECEDING AND CURRENT ROW"]}
+    end
+
+    test "raises on frame macro that does not expand to fragment" do
+      assert_raise Ecto.Query.CompileError, ~r"expected a dynamic or fragment in `:frame`", fn ->
+        Code.eval_quoted(
+          quote do
+            import Ecto.Query
+            import unquote(__MODULE__)
+
+            "q" |> windows([p], w: [frame: invalid_frame()])
+          end
+        )
+      end
+    end
   end
 
   describe "at runtime" do