test: add failing test for an aggregate of a calculation (#92)

An error occurs at compile time:

== Compilation error in file test/support/schema.ex ==
** (MatchError) no match of right hand side value: {:error, "Must provide field type for max"}
    lib/resource/resource.ex:2278: AshGraphql.Resource.filterable?/2
    (elixir 1.15.4) lib/enum.ex:4265: Enum.filter_list/2
    (elixir 1.15.4) lib/enum.ex:4266: Enum.filter_list/2
    lib/resource/resource.ex:2229: AshGraphql.Resource.aggregate_filter_fields/2
    lib/resource/resource.ex:2195: AshGraphql.Resource.resource_filter_fields/2
    lib/resource/resource.ex:1159: AshGraphql.Resource.args/5
    lib/resource/resource.ex:425: anonymous fn/6 in AshGraphql.Resource.queries/5
    (elixir 1.15.4) lib/enum.ex:1693: Enum."-map/2-lists^map/1-1-"/2

test/read_test.exs

@@ -594,6 +594,44 @@ defmodule AshGraphql.ReadTest do
     assert %{data: %{"getCompositePrimaryKey" => %{"id" => ^id}}} = result
   end
 
+  test "aggregate of a calculation" do
+    post =
+      AshGraphql.Test.Post
+      |> Ash.Changeset.for_create(:create,
+        text: "foo",
+        published: true,
+        score: 9.8
+      )
+      |> AshGraphql.Test.Api.create!()
+
+    post =
+      AshGraphql.Test.Post
+      |> Ash.Changeset.for_create(:create, text: "foo", published: true)
+      |> AshGraphql.Test.Api.create!()
+
+    AshGraphql.Test.Comment
+    |> Ash.Changeset.for_create(:create, %{text: "stuff"})
+    |> Ash.Changeset.force_change_attribute(:post_id, post.id)
+    |> AshGraphql.Test.Api.create!()
+
+    resp =
+      """
+      query Post($id: ID!) {
+        getPost(id: $id) {
+          latestCommentAt
+        }
+      }
+      """
+      |> Absinthe.run(AshGraphql.Test.Schema,
+        variables: %{
+          "id" => post.id
+        }
+      )
+
+    assert {:ok, result} = resp
+    assert result[:data]["getPost"]["latestCommentAt"]
+  end
+
   test "a read with custom types works" do
     AshGraphql.Test.Post
     |> Ash.Changeset.for_create(:create,

test/support/resources/comment.ex

@@ -38,6 +38,16 @@ defmodule AshGraphql.Test.Comment do
       writable?(false)
       default(:comment)
     end
+
+    create_timestamp(:created_at)
+  end
+
+  calculations do
+    calculate(
+      :timestamp,
+      :utc_datetime_usec,
+      expr(created_at)
+    )
   end
 
   relationships do

test/support/resources/post.ex

@@ -365,6 +365,7 @@ defmodule AshGraphql.Test.Post do
 
   aggregates do
     count(:comment_count, :comments)
+    max(:latest_comment_at, [:comments], :timestamp)
   end
 
   relationships do