Fix longer sequence name detection for serial columns (#28339)

We already found the longer sequence name, but we could not consider
whether it was the sequence name created by serial type due to missed a
max identifier length limitation. I've addressed the sequence name
consideration to respect the max identifier length.

Fixes #28332.

activerecord/CHANGELOG.md

+*   Fix longer sequence name detection for serial columns.
+
+    Fixes #28332.
+
+    *Ryuta Kamizono*
+
 *   MySQL: Don't lose `auto_increment: true` in the `db/schema.rb`.
 
     Fixes #30894.

activerecord/lib/active_record/connection_adapters/column.rb

@@ -15,7 +15,7 @@ class Column
       # +default+ is the type-casted default value, such as +new+ in <tt>sales_stage varchar(20) default 'new'</tt>.
       # +sql_type_metadata+ is various information about the type of the column
       # +null+ determines if this column allows +NULL+ values.
-      def initialize(name, default, sql_type_metadata = nil, null = true, table_name = nil, default_function = nil, collation = nil, comment: nil)
+      def initialize(name, default, sql_type_metadata = nil, null = true, table_name = nil, default_function = nil, collation = nil, comment: nil, **)
         @name = name.freeze
         @table_name = table_name
         @sql_type_metadata = sql_type_metadata

activerecord/lib/active_record/connection_adapters/postgresql/column.rb

@@ -7,6 +7,11 @@ class PostgreSQLColumn < Column #:nodoc:
       delegate :array, :oid, :fmod, to: :sql_type_metadata
       alias :array? :array
 
+      def initialize(*, max_identifier_length: 63, **)
+        super
+        @max_identifier_length = max_identifier_length
+      end
+
       def serial?
         return unless default_function
 
@@ -15,8 +20,23 @@ def serial?
         end
       end
 
+      protected
+        attr_reader :max_identifier_length
+
       private
         def sequence_name_from_parts(table_name, column_name, suffix)
+          over_length = [table_name, column_name, suffix].map(&:length).sum + 2 - max_identifier_length
+
+          if over_length > 0
+            column_name_length = [(max_identifier_length - suffix.length - 2) / 2, column_name.length].min
+            over_length -= column_name.length - column_name_length
+            column_name = column_name[0, column_name_length - [over_length, 0].min]
+          end
+
+          if over_length > 0
+            table_name = table_name[0, table_name.length - over_length]
+          end
+
           "#{table_name}_#{column_name}_#{suffix}"
         end
     end

activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb

@@ -617,7 +617,8 @@ def new_column_from_field(table_name, field)
               table_name,
               default_function,
               collation,
-              comment: comment.presence
+              comment: comment.presence,
+              max_identifier_length: max_identifier_length
             )
           end
 

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -352,10 +352,11 @@ def extensions
       end
 
       # Returns the configured supported identifier length supported by PostgreSQL
-      def table_alias_length
+      def max_identifier_length
         @max_identifier_length ||= query_value("SHOW max_identifier_length", "SCHEMA").to_i
       end
-      alias index_name_length table_alias_length
+      alias table_alias_length max_identifier_length
+      alias index_name_length max_identifier_length
 
       # Set the authorized user for this session
       def session_auth=(user)

activerecord/test/cases/adapters/postgresql/serial_test.rb

@@ -121,4 +121,36 @@ def test_schema_dump_with_collided_sequence_name
       assert_match %r{t\.bigserial\s+"bar_baz_id",\s+null: false$}, output
     end
   end
+
+  class LongerSequenceNameDetectionTest < ActiveRecord::PostgreSQLTestCase
+    include SchemaDumpingHelper
+
+    def setup
+      @table_name = "long_table_name_to_test_sequence_name_detection_for_serial_cols"
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table @table_name, force: true do |t|
+        t.serial :seq
+        t.bigserial :bigseq
+      end
+    end
+
+    def teardown
+      @connection.drop_table @table_name, if_exists: true
+    end
+
+    def test_serial_columns
+      columns = @connection.columns(@table_name)
+      columns.each do |column|
+        assert_equal :integer, column.type
+        assert column.serial?
+      end
+    end
+
+    def test_schema_dump_with_long_table_name
+      output = dump_table_schema @table_name
+      assert_match %r{create_table "#{@table_name}", force: :cascade}, output
+      assert_match %r{t\.serial\s+"seq",\s+null: false$}, output
+      assert_match %r{t\.bigserial\s+"bigseq",\s+null: false$}, output
+    end
+  end
 end