Allow adding bigint foreign keys referencing integer primary keys

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## master (unreleased)
 
+- Allow adding bigint foreign keys referencing integer primary keys
 - Fix `add_reference_concurrently` to check for mismatched key types
 
 ## 0.14.1 (2024-02-21)

lib/online_migrations/command_checker.rb

@@ -854,8 +854,14 @@ def check_mismatched_foreign_key_type(table_name, column_name, type, **options)
           if connection.table_exists?(foreign_table_name)
             primary_key = options[:primary_key] || connection.primary_key(foreign_table_name)
             primary_key_column = column_for(foreign_table_name, primary_key)
+            return if primary_key_column.nil?
 
-            if primary_key_column && type != primary_key_column.sql_type.to_sym
+            primary_key_type = primary_key_column.sql_type.to_sym
+            # Having bigint foreign keys is safe and people should
+            # detect integer primary keys via some other tools.
+            return if type == :bigint && primary_key_type == :integer
+
+            if type != primary_key_type
               raise_error :mismatched_foreign_key_type,
                 table_name: table_name, column_name: column_name
             end

test/command_checker/add_reference_test.rb

@@ -96,6 +96,17 @@ def test_add_reference_concurrently_with_mismatching_type
       MSG
     end
 
+    class AddReferenceFromBigintToInteger < TestMigration
+      def change
+        add_reference :projects, :user, type: :bigint, index: false
+      end
+    end
+
+    def test_add_reference_from_bigint_to_integer
+      @connection.change_column(:users, :id, :integer)
+      assert_safe AddReferenceFromBigintToInteger
+    end
+
     class AddReferenceForeignKey < TestMigration
       def change
         add_reference :projects, :user, index: false, foreign_key: true