MySQL: Don't lose `auto_increment: true` in the `db/schema.rb`

Currently `AUTO_INCREMENT` is implicitly used in the default primary key
definition. But `AUTO_INCREMENT` is not only used for single column
primary key, but also for composite primary key. In that case,
`auto_increment: true` should be dumped explicitly in the
`db/schema.rb`.

Fixes #30894.

1 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
index 95eb77aea4..d23178e43c 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
@@ -8,6 +8,7 @@ module ActiveRecord
           def prepare_column_options(column)
             spec = super
             spec[:unsigned] = "true" if column.unsigned?
+            spec[:auto_increment] = "true" if column.auto_increment?
 
             if @connection.supports_virtual_columns? && column.virtual?
               spec[:as] = extract_expression_for_virtual_column(column)
@@ -18,6 +19,12 @@ module ActiveRecord
             spec
           end
 
+          def column_spec_for_primary_key(column)
+            spec = super
+            spec.delete(:auto_increment) if column.type == :integer && column.auto_increment?
+            spec
+          end
+
           def default_primary_key?(column)
             super && column.auto_increment? && !column.unsigned?
           end