Restore the behaviour of the compatibility layer for integer-like PKs

The PR #27384 changed migration compatibility behaviour.

```ruby
class CreateMasterData < ActiveRecord::Migration[5.0]
  def change
    create_table :master_data, id: :integer do |t|
      t.string :name
    end
  end
end

```

Previously this migration created non-autoincremental primary key
expected. But after the PR, the primary key changed to autoincremental,
it is unexpected.

This change restores the behaviour of the compatibility layer.

6 files changed, 111 insertions, 174 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
index c3e182b43d..0443bd8bdd 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
@@ -42,7 +42,7 @@ module ActiveRecord
         # a record (as primary keys cannot be +nil+). This might be done via the
         # +SecureRandom.uuid+ method and a +before_save+ callback, for instance.
         def primary_key(name, type = :primary_key, **options)
-          options[:auto_increment] = true if [:primary_key, :integer, :bigint].include?(type) && !options.key?(:default)
+          options[:auto_increment] = true if [:integer, :bigint].include?(type) && !options.key?(:default)
           if type == :uuid
             options[:default] = options.fetch(:default, "gen_random_uuid()")
           elsif options.delete(:auto_increment) == true && %i(integer bigint).include?(type)
diff --git a/activerecord/lib/active_record/migration/compatibility.rb b/activerecord/lib/active_record/migration/compatibility.rb
index ffeca2c91e..f6c9127d34 100644
--- a/activerecord/lib/active_record/migration/compatibility.rb
+++ b/activerecord/lib/active_record/migration/compatibility.rb
@@ -21,6 +21,12 @@ module ActiveRecord
             end
           end
 
+          unless adapter_name == "Mysql2" && options[:id] == :bigint
+            if [:integer, :bigint].include?(options[:id]) && !options.key?(:default)
+              options[:default] = nil
+            end
+          end
+
           # Since 5.1 Postgres adapter uses bigserial type for primary
           # keys by default and MySQL uses bigint. This compat layer makes old migrations utilize
           # serial/int type instead -- the way it used to work before 5.1.
diff --git a/activerecord/test/cases/adapters/mysql2/legacy_migration_test.rb b/activerecord/test/cases/adapters/mysql2/legacy_migration_test.rb
deleted file mode 100644
index 5d3125c2be..0000000000
--- a/activerecord/test/cases/adapters/mysql2/legacy_migration_test.rb
+++ /dev/null
@@ -1,60 +0,0 @@
-require "cases/helper"
-
-class MysqlLegacyMigrationTest < ActiveRecord::Mysql2TestCase
-  self.use_transactional_tests = false
-
-  class GenerateTableWithoutBigint < ActiveRecord::Migration[5.0]
-    def change
-      create_table :legacy_integer_pk do |table|
-        table.string :foo
-      end
-
-      create_table :override_pk, id: :bigint do |table|
-        table.string :bar
-      end
-    end
-  end
-
-  def setup
-    super
-    @connection = ActiveRecord::Base.connection
-
-    @migration_verbose_old = ActiveRecord::Migration.verbose
-    ActiveRecord::Migration.verbose = false
-
-    migrations = [GenerateTableWithoutBigint.new(nil, 1)]
-
-    ActiveRecord::Migrator.new(:up, migrations).migrate
-  end
-
-  def teardown
-    ActiveRecord::Migration.verbose = @migration_verbose_old
-    @connection.drop_table("legacy_integer_pk")
-    @connection.drop_table("override_pk")
-    ActiveRecord::SchemaMigration.delete_all rescue nil
-    super
-  end
-
-  def test_create_table_uses_integer_as_pkey_by_default
-    col = column(:legacy_integer_pk, :id)
-    assert_equal "int(11)", sql_type_for(col)
-    assert col.auto_increment?
-  end
-
-  def test_create_tables_respects_pk_column_type_override
-    col = column(:override_pk, :id)
-    assert_equal "bigint(20)", sql_type_for(col)
-  end
-
-  private
-
-    def column(table_name, column_name)
-      ActiveRecord::Base.connection
-        .columns(table_name.to_s)
-        .detect { |c| c.name == column_name.to_s }
-    end
-
-    def sql_type_for(col)
-      col && col.sql_type
-    end
-end
diff --git a/activerecord/test/cases/adapters/postgresql/legacy_migration_test.rb b/activerecord/test/cases/adapters/postgresql/legacy_migration_test.rb
deleted file mode 100644
index 082fe95053..0000000000
--- a/activerecord/test/cases/adapters/postgresql/legacy_migration_test.rb
+++ /dev/null
@@ -1,54 +0,0 @@
-require "cases/helper"
-
-class PostgresqlLegacyMigrationTest < ActiveRecord::PostgreSQLTestCase
-  class GenerateTableWithoutBigserial < ActiveRecord::Migration[5.0]
-    def change
-      create_table :legacy_integer_pk do |table|
-        table.string :foo
-      end
-
-      create_table :override_pk, id: :bigint do |table|
-        table.string :bar
-      end
-    end
-  end
-
-  def setup
-    super
-
-    @migration_verbose_old = ActiveRecord::Migration.verbose
-    ActiveRecord::Migration.verbose = false
-
-    migrations = [GenerateTableWithoutBigserial.new(nil, 1)]
-    ActiveRecord::Migrator.new(:up, migrations).migrate
-  end
-
-  def teardown
-    ActiveRecord::Migration.verbose = @migration_verbose_old
-
-    super
-  end
-
-  def test_create_table_uses_serial_as_pkey_by_default
-    col = column(:legacy_integer_pk, :id)
-    assert_equal "integer", sql_type_for(col)
-    assert col.serial?
-  end
-
-  def test_create_tables_respects_pk_column_type_override
-    col = column(:override_pk, :id)
-    assert_equal "bigint", sql_type_for(col)
-  end
-
-  private
-
-    def column(table_name, column_name)
-      ActiveRecord::Base.connection.
-        columns(table_name.to_s).
-        detect { |c| c.name == column_name.to_s }
-    end
-
-    def sql_type_for(col)
-      col && col.sql_type
-    end
-end
diff --git a/activerecord/test/cases/adapters/sqlite3/legacy_migration_test.rb b/activerecord/test/cases/adapters/sqlite3/legacy_migration_test.rb
deleted file mode 100644
index fcca8d66b5..0000000000
--- a/activerecord/test/cases/adapters/sqlite3/legacy_migration_test.rb
+++ /dev/null
@@ -1,59 +0,0 @@
-require "cases/helper"
-
-class SqliteLegacyMigrationTest < ActiveRecord::SQLite3TestCase
-  self.use_transactional_tests = false
-
-  class GenerateTableWithoutBigint < ActiveRecord::Migration[5.0]
-    def change
-      create_table :legacy_integer_pk do |table|
-        table.string :foo
-      end
-
-      create_table :override_pk, id: :bigint do |table|
-        table.string :bar
-      end
-    end
-  end
-
-  def setup
-    super
-    @connection = ActiveRecord::Base.connection
-
-    @migration_verbose_old = ActiveRecord::Migration.verbose
-    ActiveRecord::Migration.verbose = false
-
-    migrations = [GenerateTableWithoutBigint.new(nil, 1)]
-
-    ActiveRecord::Migrator.new(:up, migrations).migrate
-  end
-
-  def teardown
-    ActiveRecord::Migration.verbose = @migration_verbose_old
-    @connection.drop_table("legacy_integer_pk")
-    @connection.drop_table("override_pk")
-    ActiveRecord::SchemaMigration.delete_all rescue nil
-    super
-  end
-
-  def test_create_table_uses_integer_as_pkey_by_default
-    col = column(:legacy_integer_pk, :id)
-    assert_equal "INTEGER", sql_type_for(col)
-    assert primary_key?(:legacy_integer_pk, "id"), "id is not primary key"
-  end
-
-  private
-
-    def column(table_name, column_name)
-      ActiveRecord::Base.connection
-        .columns(table_name.to_s)
-        .detect { |c| c.name == column_name.to_s }
-    end
-
-    def sql_type_for(col)
-      col && col.sql_type
-    end
-
-    def primary_key?(table_name, column)
-      ActiveRecord::Base.connection.execute("PRAGMA table_info(#{table_name})").find { |col| col["name"] == column }["pk"] == 1
-    end
-end
diff --git a/activerecord/test/cases/migration/compatibility_test.rb b/activerecord/test/cases/migration/compatibility_test.rb
index 9296f3da90..fc3ec47825 100644
--- a/activerecord/test/cases/migration/compatibility_test.rb
+++ b/activerecord/test/cases/migration/compatibility_test.rb
@@ -1,4 +1,5 @@
 require "cases/helper"
+require "support/schema_dumping_helper"
 
 module ActiveRecord
   class Migration
@@ -111,3 +112,106 @@ module ActiveRecord
     end
   end
 end
+
+class LegacyPrimaryKeyTest < ActiveRecord::TestCase
+  include SchemaDumpingHelper
+
+  self.use_transactional_tests = false
+
+  class LegacyPrimaryKey < ActiveRecord::Base
+  end
+
+  def setup
+    @migration = nil
+    @verbose_was = ActiveRecord::Migration.verbose
+    ActiveRecord::Migration.verbose = false
+  end
+
+  def teardown
+    @migration.migrate(:down) if @migration
+    ActiveRecord::Migration.verbose = @verbose_was
+    ActiveRecord::SchemaMigration.delete_all rescue nil
+    LegacyPrimaryKey.reset_column_information
+  end
+
+  def test_legacy_primary_key_should_be_auto_incremented
+    @migration = Class.new(ActiveRecord::Migration[5.0]) {
+      def change
+        create_table :legacy_primary_keys do |t|
+        end
+      end
+    }.new
+
+    @migration.migrate(:up)
+
+    legacy_pk = LegacyPrimaryKey.columns_hash["id"]
+    assert_not legacy_pk.bigint?
+    assert_not legacy_pk.null
+
+    record1 = LegacyPrimaryKey.create!
+    assert_not_nil record1.id
+
+    record1.destroy
+
+    record2 = LegacyPrimaryKey.create!
+    assert_not_nil record2.id
+    assert_operator record2.id, :>, record1.id
+  end
+
+  def test_legacy_integer_primary_key_should_not_be_auto_incremented
+    skip if current_adapter?(:SQLite3Adapter)
+
+    @migration = Class.new(ActiveRecord::Migration[5.0]) {
+      def change
+        create_table :legacy_primary_keys, id: :integer do |t|
+        end
+      end
+    }.new
+
+    @migration.migrate(:up)
+
+    assert_raises(ActiveRecord::NotNullViolation) do
+      LegacyPrimaryKey.create!
+    end
+
+    schema = dump_table_schema "legacy_primary_keys"
+    assert_match %r{create_table "legacy_primary_keys", id: :integer, default: nil}, schema
+  end
+
+  if current_adapter?(:Mysql2Adapter)
+    def test_legacy_bigint_primary_key_should_be_auto_incremented
+      @migration = Class.new(ActiveRecord::Migration[5.0]) {
+        def change
+          create_table :legacy_primary_keys, id: :bigint
+        end
+      }.new
+
+      @migration.migrate(:up)
+
+      legacy_pk = LegacyPrimaryKey.columns_hash["id"]
+      assert legacy_pk.bigint?
+      assert legacy_pk.auto_increment?
+
+      schema = dump_table_schema "legacy_primary_keys"
+      assert_match %r{create_table "legacy_primary_keys", (?!id: :bigint, default: nil)}, schema
+    end
+  else
+    def test_legacy_bigint_primary_key_should_not_be_auto_incremented
+      @migration = Class.new(ActiveRecord::Migration[5.0]) {
+        def change
+          create_table :legacy_primary_keys, id: :bigint do |t|
+          end
+        end
+      }.new
+
+      @migration.migrate(:up)
+
+      assert_raises(ActiveRecord::NotNullViolation) do
+        LegacyPrimaryKey.create!
+      end
+
+      schema = dump_table_schema "legacy_primary_keys"
+      assert_match %r{create_table "legacy_primary_keys", id: :bigint, default: nil}, schema
+    end
+  end
+end