Fix type casting column default in `change_column`

Since #31230, `change_column` is executed as a bulk statement.

That caused incorrect type casting column default by looking up the
before changed type, not the after changed type.

In a bulk statement, we can't use `change_column_default_for_alter` if
the statement changes the column type.

This fixes the type casting to use the constructed target sql_type.

Fixes #34938.

1 files changed, 13 insertions, 1 deletions

diff --git a/activerecord/test/cases/adapters/postgresql/array_test.rb b/activerecord/test/cases/adapters/postgresql/array_test.rb
index b12055a40a..2e7a4b498f 100644
--- a/activerecord/test/cases/adapters/postgresql/array_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/array_test.rb
@@ -17,7 +17,7 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     enable_extension!("hstore", @connection)
 
     @connection.transaction do
-      @connection.create_table("pg_arrays") do |t|
+      @connection.create_table "pg_arrays", force: true do |t|
         t.string "tags", array: true, limit: 255
         t.integer "ratings", array: true
         t.datetime :datetimes, array: true
@@ -112,6 +112,18 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     assert_predicate column, :array?
   end
 
+  def test_change_column_from_non_array_to_array
+    @connection.add_column :pg_arrays, :snippets, :string
+    @connection.change_column :pg_arrays, :snippets, :text, array: true, default: [], using: "string_to_array(\"snippets\", ',')"
+
+    PgArray.reset_column_information
+    column = PgArray.columns_hash["snippets"]
+
+    assert_equal :text, column.type
+    assert_equal [], PgArray.column_defaults["snippets"]
+    assert_predicate column, :array?
+  end
+
   def test_change_column_cant_make_non_array_column_to_array
     @connection.add_column :pg_arrays, :a_string, :string
     assert_raises ActiveRecord::StatementInvalid do