Allow mismatching bigint FK to integer PK types

lib/online_migrations/command_checker.rb

@@ -855,7 +855,8 @@ def check_mismatched_foreign_key_type(table_name, column_name, type, **options)
             primary_key = options[:primary_key] || connection.primary_key(foreign_table_name)
             primary_key_column = column_for(foreign_table_name, primary_key)
 
-            if primary_key_column && type != primary_key_column.sql_type.to_sym
+            if primary_key_column && type != (primary_key_column_type = primary_key_column.sql_type.to_sym) &&
+               !(type == :bigint && primary_key_column_type == :integer)
               raise_error :mismatched_foreign_key_type,
                 table_name: table_name, column_name: column_name
             end

test/command_checker/add_reference_test.rb

@@ -56,6 +56,22 @@ def test_add_reference_no_index
       assert_safe AddReferenceNoIndex
     end
 
+    class AddReferenceFromTypeBigIntToInt < TestMigration
+      disable_ddl_transaction!
+
+      def change
+        add_reference :projects, :user, type: :bigint, index: false
+      end
+    end
+
+    def test_add_reference_from_type_bigint_to_int
+      @connection.drop_table(:users, if_exists: true)
+      @connection.create_table(:users, id: :integer, force: :cascade)
+
+      assert_equal :integer, @connection.columns(:users).find { |c| c.name == "id" }.sql_type.to_sym
+      assert_safe AddReferenceFromTypeBigIntToInt
+    end
+
     class AddReferenceIndexConcurrently < TestMigration
       disable_ddl_transaction!
 
@@ -89,7 +105,7 @@ def change
     end
 
     def test_add_reference_concurrently_with_mismatching_type
-      assert_not_equal :uuid, @connection.columns(:users).find { |c| c.name == "id" }.type
+      assert_not_equal :uuid, @connection.columns(:users).find { |c| c.name == "id" }.sql_type.to_sym
       assert_unsafe AddReferenceConcurrentlyWithMismatchingType, <<~MSG
         projects.user_id references a column of different type - foreign keys should be of the same type as the referenced primary key.
         Otherwise, there's a risk of errors caused by IDs representable by one type but not the other.