fix: Use new attribute source in down migration (#604)

closes: #582

When an attribute is renamed, alongside other changes to it (like changing default or not null constraint), the generated up migration first renames the column, then modifies it.

For the generated down migration, the order of operations is reversed, so we need to use the new column name when modifying the column, before renaming it back.

Author: awerment

lib/migration_generator/operation.ex

@@ -752,7 +752,7 @@ defmodule AshPostgres.MigrationGenerator.Operation do
       up(%{
         op
         | old_attribute: op.new_attribute,
-          new_attribute: op.old_attribute,
+          new_attribute: Map.put(op.old_attribute, :source, op.new_attribute.source),
           old_multitenancy: op.multitenancy,
           multitenancy: op.old_multitenancy
       })

test/migration_generator_test.exs

@@ -825,8 +825,41 @@ defmodule AshPostgres.MigrationGeneratorTest do
                Enum.sort(Path.wildcard("test_migration_path/**/*_migrate_resources*.exs"))
                |> Enum.reject(&String.contains?(&1, "extensions"))
 
-      assert File.read!(file2) =~ ~S[rename table(:posts, prefix: "example"), :title, to: :name]
-      assert File.read!(file2) =~ ~S[modify :title, :text, null: true, default: nil]
+      contents = File.read!(file2)
+
+      [up_side, down_side] = String.split(contents, "def down", parts: 2)
+
+      up_side_parts =
+        String.split(up_side, "\n", trim: true)
+        |> Enum.map(&String.trim/1)
+
+      up_rename_index =
+        Enum.find_index(up_side_parts, fn x ->
+          x == ~S[rename table(:posts, prefix: "example"), :title, to: :name]
+        end)
+
+      up_modify_index =
+        Enum.find_index(up_side_parts, fn x ->
+          x == ~S[modify :name, :text, null: false, default: "fred"]
+        end)
+
+      assert up_rename_index < up_modify_index
+
+      down_side_parts =
+        String.split(down_side, "\n", trim: true)
+        |> Enum.map(&String.trim/1)
+
+      down_modify_index =
+        Enum.find_index(down_side_parts, fn x ->
+          x == ~S[modify :name, :text, null: true, default: nil]
+        end)
+
+      down_rename_index =
+        Enum.find_index(down_side_parts, fn x ->
+          x == ~S[rename table(:posts, prefix: "example"), :name, to: :title]
+        end)
+
+      assert down_modify_index < down_rename_index
     end
   end