Load environment file in `dbconsole` command

Currently the environment file is not loaded in `dbconsole` command.
Therefore, for example, if use encrypted secrets values in database.yml,
`read_encrypted_secrets` will not be true, so the value can not be
used correctly.

Fixes #29717

railties/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Load environment file in `dbconsole` command.
+
+    Fixes #29717
+
+    *Yuji Yaginuma*
+
 *   Add `rails secrets:show` command.
 
     *Yuji Yaginuma*

railties/lib/rails/commands/dbconsole/dbconsole_command.rb

@@ -148,6 +148,7 @@ module Rails
       def perform
         extract_environment_option_from_argument
 
+        require_application_and_environment!
         Rails::DBConsole.start(options)
       end
     end

railties/test/application/dbconsole_test.rb

@@ -0,0 +1,66 @@
+require "isolation/abstract_unit"
+begin
+  require "pty"
+rescue LoadError
+end
+
+module ApplicationTests
+  class DBConsoleTest < ActiveSupport::TestCase
+    include ActiveSupport::Testing::Isolation
+
+    def setup
+      build_app
+    end
+
+    def teardown
+      teardown_app
+    end
+
+    def test_use_value_defined_in_environment_file_in_database_yml
+      skip "PTY unavailable" unless available_pty?
+      Dir.chdir(app_path) do
+        app_file "config/database.yml", <<-YAML
+          development:
+             database: <%= Rails.application.config.database %>
+             adapter: sqlite3
+             pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
+             timeout: 5000
+        YAML
+
+        app_file "config/environments/development.rb", <<-RUBY
+          Rails.application.configure do
+            config.database = "db/development.sqlite3"
+          end
+        RUBY
+      end
+
+      master, slave = PTY.open
+      spawn_dbconsole(slave)
+      assert_output("sqlite>", master)
+    ensure
+      master.puts ".exit"
+    end
+
+    private
+      def spawn_dbconsole(fd)
+        Process.spawn("#{app_path}/bin/rails dbconsole", in: fd, out: fd, err: fd)
+      end
+
+      def assert_output(expected, io, timeout = 5)
+        timeout = Time.now + timeout
+
+        output = ""
+        until output.include?(expected) || Time.now > timeout
+          if IO.select([io], [], [], 0.1)
+            output << io.read(1)
+          end
+        end
+
+        assert_includes output, expected, "#{expected.inspect} expected, but got:\n\n#{output}"
+      end
+
+      def available_pty?
+        defined?(PTY) && PTY.respond_to?(:open)
+      end
+  end
+end