Dump the database schema containing the current Rails version

Since #42297, Rails now generates
datetime columns on MySQL with a default precision of 6. This means
that users upgrading to Rails 7.0 from 6.1, when loading the database
schema, would get the new precision value, which would not match the
production schema.

To avoid problems like this in the future,
Rails will now freeze `ActiveRecord::Schema` class to
be the 7.0 implementation, and will allow access to other version
using the same mechanism of `ActiveRecord::Migration`.

The schema dumper will generate the new format which will include the
Rails version and will look like this:

```
ActiveRecord::Schema[7.0].define
```

Related to #43934 and #43909.

activerecord/lib/active_record/railties/databases.rake

@@ -548,7 +548,7 @@ db_namespace = namespace :db do
     # desc "Recreate the test database from an existent schema file (schema.rb or structure.sql, depending on `config.active_record.schema_format`)"
     task load_schema: %w(db:test:purge) do
       should_reconnect = ActiveRecord::Base.connection_pool.active_connection?
-      ActiveRecord::Schema.verbose = false
+      ActiveRecord::Schema::Current.verbose = false
       ActiveRecord::Base.configurations.configs_for(env_name: "test").each do |db_config|
         ActiveRecord::Tasks::DatabaseTasks.load_schema(db_config)
       end
@@ -584,7 +584,7 @@ db_namespace = namespace :db do
       namespace :load_schema do
         task name => "db:test:purge:#{name}" do
           should_reconnect = ActiveRecord::Base.connection_pool.active_connection?
-          ActiveRecord::Schema.verbose = false
+          ActiveRecord::Schema::Current.verbose = false
           db_config = ActiveRecord::Base.configurations.configs_for(env_name: "test", name: name)
           ActiveRecord::Tasks::DatabaseTasks.load_schema(db_config)
         ensure

activerecord/lib/active_record/schema.rb

@@ -10,7 +10,7 @@ module ActiveRecord
   #
   # Usage:
   #
-  #   ActiveRecord::Schema.define do
+  #   ActiveRecord::Schema[7.0].define do
   #     create_table :authors do |t|
   #       t.string :name, null: false
   #     end
@@ -29,33 +29,51 @@ module ActiveRecord
   #
   # ActiveRecord::Schema is only supported by database adapters that also
   # support migrations, the two features being very similar.
-  class Schema < Migration::Current
-    # Eval the given block. All methods available to the current connection
-    # adapter are available within the block, so you can easily use the
-    # database definition DSL to build up your schema (
-    # {create_table}[rdoc-ref:ConnectionAdapters::SchemaStatements#create_table],
-    # {add_index}[rdoc-ref:ConnectionAdapters::SchemaStatements#add_index], etc.).
-    #
-    # The +info+ hash is optional, and if given is used to define metadata
-    # about the current schema (currently, only the schema's version):
-    #
-    #   ActiveRecord::Schema.define(version: 2038_01_19_000001) do
-    #     ...
-    #   end
-    def self.define(info = {}, &block)
-      new.define(info, &block)
-    end
+  class Schema < Migration[7.0]
+    module Definition
+      extend ActiveSupport::Concern
+
+      module ClassMethods
+        # Eval the given block. All methods available to the current connection
+        # adapter are available within the block, so you can easily use the
+        # database definition DSL to build up your schema (
+        # {create_table}[rdoc-ref:ConnectionAdapters::SchemaStatements#create_table],
+        # {add_index}[rdoc-ref:ConnectionAdapters::SchemaStatements#add_index], etc.).
+        #
+        # The +info+ hash is optional, and if given is used to define metadata
+        # about the current schema (currently, only the schema's version):
+        #
+        #   ActiveRecord::Schema[7.0].define(version: 2038_01_19_000001) do
+        #     ...
+        #   end
+        def define(info = {}, &block)
+          new.define(info, &block)
+        end
+      end
 
-    def define(info, &block) # :nodoc:
-      instance_eval(&block)
+      def define(info, &block) # :nodoc:
+        instance_eval(&block)
 
-      if info[:version].present?
-        connection.schema_migration.create_table
-        connection.assume_migrated_upto_version(info[:version])
+        if info[:version].present?
+          connection.schema_migration.create_table
+          connection.assume_migrated_upto_version(info[:version])
+        end
+
+        ActiveRecord::InternalMetadata.create_table
+        ActiveRecord::InternalMetadata[:environment] = connection.migration_context.current_environment
       end
+    end
 
-      ActiveRecord::InternalMetadata.create_table
-      ActiveRecord::InternalMetadata[:environment] = connection.migration_context.current_environment
+    include Definition
+
+    class Current < Migration::Current
+      include Definition
+    end
+
+    def self.[](version)
+      Class.new(Migration::Compatibility.find(version)) do
+        include Definition
+      end
     end
   end
 end

activerecord/lib/active_record/schema_dumper.rb

@@ -73,23 +73,23 @@ def define_params
         @version ? "version: #{formatted_version}" : ""
       end
 
+      # TODO: Fix dumper
       def header(stream)
-        stream.puts <<HEADER
-# This file is auto-generated from the current state of the database. Instead
-# of editing this file, please use the migrations feature of Active Record to
-# incrementally modify your database, and then regenerate this schema definition.
-#
-# This file is the source Rails uses to define your schema when running `bin/rails
-# db:schema:load`. When creating a new database, `bin/rails db:schema:load` tends to
-# be faster and is potentially less error prone than running all of your
-# migrations from scratch. Old migrations may fail to apply correctly if those
-# migrations use external dependencies or application code.
-#
-# It's strongly recommended that you check this file into your version control system.
-
-ActiveRecord::Schema.define(#{define_params}) do
-
-HEADER
+        stream.puts <<~HEADER
+          # This file is auto-generated from the current state of the database. Instead
+          # of editing this file, please use the migrations feature of Active Record to
+          # incrementally modify your database, and then regenerate this schema definition.
+          #
+          # This file is the source Rails uses to define your schema when running `bin/rails
+          # db:schema:load`. When creating a new database, `bin/rails db:schema:load` tends to
+          # be faster and is potentially less error prone than running all of your
+          # migrations from scratch. Old migrations may fail to apply correctly if those
+          # migrations use external dependencies or application code.
+          #
+          # It's strongly recommended that you check this file into your version control system.
+
+          ActiveRecord::Schema[#{ActiveRecord::Migration.current_version}].define(#{define_params}) do
+        HEADER
       end
 
       def trailer(stream)

activerecord/test/cases/ar_schema_test.rb → activerecord/test/cases/active_record_schema_test.rb

@@ -37,8 +37,28 @@ def test_has_primary_key
     ActiveRecord::Base.primary_key_prefix_type = old_primary_key_prefix_type
   end
 
+  def test_schema_without_version_is_the_7_0_schema
+    schema_class = ActiveRecord::Schema
+    assert schema_class < ActiveRecord::Migration[7.0]
+    assert_not schema_class < ActiveRecord::Migration[6.1]
+    assert schema_class < ActiveRecord::Schema::Definition
+  end
+
+  def test_current_schema_is_the_current_version_schema
+    schema_class = ActiveRecord::Schema::Current
+    assert schema_class < ActiveRecord::Migration[ActiveRecord::Migration.current_version]
+    assert_not schema_class < ActiveRecord::Migration[6.1]
+    assert schema_class < ActiveRecord::Schema::Definition
+  end
+
+  def test_schema_version_accessor
+    schema_class = ActiveRecord::Schema[6.1]
+    assert schema_class < ActiveRecord::Migration[6.1]
+    assert schema_class < ActiveRecord::Schema::Definition
+  end
+
   def test_schema_define
-    ActiveRecord::Schema.define(version: 7) do
+    ActiveRecord::Schema::Current.define(version: 7) do
       create_table :fruits do |t|
         t.column :color, :string
         t.column :fruit_size, :string  # NOTE: "size" is reserved in Oracle
@@ -57,7 +77,7 @@ def test_schema_define_with_table_name_prefix
     ActiveRecord::Base.table_name_prefix = "nep_"
     @schema_migration.reset_table_name
     ActiveRecord::InternalMetadata.reset_table_name
-    ActiveRecord::Schema.define(version: 7) do
+    ActiveRecord::Schema::Current.define(version: 7) do
       create_table :fruits do |t|
         t.column :color, :string
         t.column :fruit_size, :string  # NOTE: "size" is reserved in Oracle
@@ -74,7 +94,7 @@ def test_schema_define_with_table_name_prefix
 
   def test_schema_raises_an_error_for_invalid_column_type
     assert_raise NoMethodError do
-      ActiveRecord::Schema.define(version: 8) do
+      ActiveRecord::Schema::Current.define(version: 8) do
         create_table :vegetables do |t|
           t.unknown :color
         end
@@ -97,7 +117,7 @@ def test_normalize_version
   end
 
   def test_schema_load_with_multiple_indexes_for_column_of_different_names
-    ActiveRecord::Schema.define do
+    ActiveRecord::Schema::Current.define do
       create_table :multiple_indexes do |t|
         t.string "foo"
         t.index ["foo"], name: "multiple_indexes_foo_1"
@@ -113,7 +133,7 @@ def test_schema_load_with_multiple_indexes_for_column_of_different_names
 
   if current_adapter?(:PostgreSQLAdapter)
     def test_timestamps_with_and_without_zones
-      ActiveRecord::Schema.define do
+      ActiveRecord::Schema::Current.define do
         create_table :has_timestamps do |t|
           t.datetime "default_format"
           t.datetime "without_time_zone"
@@ -130,7 +150,7 @@ def test_timestamps_with_and_without_zones
   end
 
   def test_timestamps_without_null_set_null_to_false_on_create_table
-    ActiveRecord::Schema.define do
+    ActiveRecord::Schema::Current.define do
       create_table :has_timestamps do |t|
         t.timestamps
       end
@@ -141,7 +161,7 @@ def test_timestamps_without_null_set_null_to_false_on_create_table
   end
 
   def test_timestamps_without_null_set_null_to_false_on_change_table
-    ActiveRecord::Schema.define do
+    ActiveRecord::Schema::Current.define do
       create_table :has_timestamps
 
       change_table :has_timestamps do |t|
@@ -155,7 +175,7 @@ def test_timestamps_without_null_set_null_to_false_on_change_table
 
   if ActiveRecord::Base.connection.supports_bulk_alter?
     def test_timestamps_without_null_set_null_to_false_on_change_table_with_bulk
-      ActiveRecord::Schema.define do
+      ActiveRecord::Schema::Current.define do
         create_table :has_timestamps
 
         change_table :has_timestamps, bulk: true do |t|
@@ -169,7 +189,7 @@ def test_timestamps_without_null_set_null_to_false_on_change_table_with_bulk
   end
 
   def test_timestamps_without_null_set_null_to_false_on_add_timestamps
-    ActiveRecord::Schema.define do
+    ActiveRecord::Schema::Current.define do
       create_table :has_timestamps
       add_timestamps :has_timestamps, default: Time.now
     end
@@ -180,7 +200,7 @@ def test_timestamps_without_null_set_null_to_false_on_add_timestamps
 
   if supports_datetime_with_precision?
     def test_timestamps_sets_precision_on_create_table
-      ActiveRecord::Schema.define do
+      ActiveRecord::Schema::Current.define do
         create_table :has_timestamps do |t|
           t.timestamps
         end
@@ -191,7 +211,7 @@ def test_timestamps_sets_precision_on_create_table
     end
 
     def test_timestamps_sets_precision_on_change_table
-      ActiveRecord::Schema.define do
+      ActiveRecord::Schema::Current.define do
         create_table :has_timestamps
 
         change_table :has_timestamps do |t|
@@ -205,7 +225,7 @@ def test_timestamps_sets_precision_on_change_table
 
     if ActiveRecord::Base.connection.supports_bulk_alter?
       def test_timestamps_sets_precision_on_change_table_with_bulk
-        ActiveRecord::Schema.define do
+        ActiveRecord::Schema::Current.define do
           create_table :has_timestamps
 
           change_table :has_timestamps, bulk: true do |t|
@@ -219,7 +239,7 @@ def test_timestamps_sets_precision_on_change_table_with_bulk
     end
 
     def test_timestamps_sets_precision_on_add_timestamps
-      ActiveRecord::Schema.define do
+      ActiveRecord::Schema::Current.define do
         create_table :has_timestamps
         add_timestamps :has_timestamps, default: Time.now
       end

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

@@ -113,7 +113,7 @@ def test_schema_dump
   def test_schema_load
     original, $stdout = $stdout, StringIO.new
 
-    ActiveRecord::Schema.define do
+    ActiveRecord::Schema::Current.define do
       create_enum :color, ["blue", "green"]
 
       change_table :postgresql_enums do |t|

activerecord/test/cases/migrator_test.rb

@@ -226,7 +226,7 @@ def test_migrations_status_with_schema_define_in_subdirectories
     schema_migration = ActiveRecord::Base.connection.schema_migration
     ActiveRecord::Migrator.migrations_paths = path
 
-    ActiveRecord::Schema.define(version: 3) do
+    ActiveRecord::Schema::Current.define(version: 3) do
     end
 
     assert_equal [

activerecord/test/cases/schema_dumper_test.rb

@@ -38,6 +38,11 @@ def test_dump_schema_information_outputs_lexically_ordered_versions
     ActiveRecord::SchemaMigration.delete_all
   end
 
+  def test_schema_dump_include_migration_version
+    output = standard_dump
+    assert_match %r{ActiveRecord::Schema\[#{ActiveRecord::Migration.current_version}\]\.define}, output
+  end
+
   def test_schema_dump
     output = standard_dump
     assert_match %r{create_table "accounts"}, output

activerecord/test/schema/mysql2_specific_schema.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   if supports_datetime_with_precision?
     create_table :datetime_defaults, force: true do |t|
       t.datetime :modified_datetime, precision: nil, default: -> { "CURRENT_TIMESTAMP" }

activerecord/test/schema/oracle_specific_schema.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   execute "drop table test_oracle_defaults" rescue nil
   execute "drop sequence test_oracle_defaults_seq" rescue nil
   execute "drop sequence companies_nonstd_seq" rescue nil

activerecord/test/schema/postgresql_specific_schema.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   enable_extension!("uuid-ossp", ActiveRecord::Base.connection)
   enable_extension!("pgcrypto",  ActiveRecord::Base.connection) if ActiveRecord::Base.connection.supports_pgcrypto_uuid?
 

activerecord/test/schema/schema.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   # ------------------------------------------------------------------- #
   #                                                                     #
   #   Please keep these create table statements in alphabetical order   #

activerecord/test/schema/sqlite_specific_schema.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   create_table :defaults, force: true do |t|
     t.date :modified_date, default: -> { "CURRENT_DATE" }
     t.date :fixed_date, default: "2004-01-01"

guides/bug_report_templates/action_mailbox_gem.rb

@@ -45,7 +45,7 @@ class TestApp < Rails::Application
 require ActiveStorage::Engine.root.join("db/migrate/20170806125915_create_active_storage_tables.rb").to_s
 require ActionMailbox::Engine.root.join("db/migrate/20180917164000_create_action_mailbox_tables.rb").to_s
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   CreateActiveStorageTables.new.change
   CreateActionMailboxTables.new.change
 end

guides/bug_report_templates/action_mailbox_main.rb

@@ -44,7 +44,7 @@ class TestApp < Rails::Application
 require ActiveStorage::Engine.root.join("db/migrate/20170806125915_create_active_storage_tables.rb").to_s
 require ActionMailbox::Engine.root.join("db/migrate/20180917164000_create_action_mailbox_tables.rb").to_s
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   CreateActiveStorageTables.new.change
   CreateActionMailboxTables.new.change
 end

guides/bug_report_templates/active_record_gem.rb

@@ -20,7 +20,7 @@
 ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
 ActiveRecord::Base.logger = Logger.new(STDOUT)
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   create_table :posts, force: true do |t|
   end
 

guides/bug_report_templates/active_record_main.rb

@@ -19,7 +19,7 @@
 ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
 ActiveRecord::Base.logger = Logger.new(STDOUT)
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   create_table :posts, force: true do |t|
   end
 

guides/bug_report_templates/active_record_migrations_gem.rb

@@ -20,7 +20,7 @@
 ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
 ActiveRecord::Base.logger = Logger.new(STDOUT)
 
-ActiveRecord::Schema.define do
+ActiveRecord::Schema::Current.define do
   create_table :payments, force: true do |t|
     t.decimal :amount, precision: 10, scale: 0, default: 0, null: false
   end