Don't allow mutations on configuration_hash

We want to introduce an object-based DSL for building and modifying
configuration objects. As part of that we want to make sure that users
don't think they can modify configuration_hash values and have them
change the configuration. For that reason we're going to freeze the
Hash here, and have modified places in tests where we were modifying
these hashes.

The commit here also adds a test for the Test Databases and in that work
we found that we were calling `Rails.env` and Active Record doesn't load
Rails.

Co-authored-by: John Crepezzi <john.crepezzi@gmail.com>

activerecord/lib/active_record/database_configurations/hash_config.rb

@@ -36,7 +36,7 @@ def config
       end
 
       def configuration_hash
-        @config
+        @config.freeze
       end
 
       # Determines whether a database configuration is for a replica / readonly

activerecord/lib/active_record/test_databases.rb

@@ -5,18 +5,25 @@
 module ActiveRecord
   module TestDatabases # :nodoc:
     ActiveSupport::Testing::Parallelization.after_fork_hook do |i|
-      create_and_load_schema(i, env_name: Rails.env)
+      create_and_load_schema(i, env_name: ActiveRecord::ConnectionHandling::DEFAULT_ENV.call.to_sym)
     end
 
     def self.create_and_load_schema(i, env_name:)
       old, ENV["VERBOSE"] = ENV["VERBOSE"], "false"
 
       ActiveRecord::Base.configurations.configs_for(env_name: env_name).each do |db_config|
-        db_config.configuration_hash[:database] += "-#{i}"
-        ActiveRecord::Tasks::DatabaseTasks.reconstruct_from_schema(db_config, ActiveRecord::Base.schema_format, nil)
+        database = "#{db_config.database}-#{i}"
+
+        db_config_copy = ActiveRecord::DatabaseConfigurations::HashConfig.new(
+          env_name,
+          db_config.spec_name,
+          db_config.configuration_hash.merge(database: database)
+        )
+
+        ActiveRecord::Tasks::DatabaseTasks.reconstruct_from_schema(db_config_copy, ActiveRecord::Base.schema_format, nil)
       end
     ensure
-      ActiveRecord::Base.establish_connection(Rails.env.to_sym)
+      ActiveRecord::Base.establish_connection(ActiveRecord::ConnectionHandling::DEFAULT_ENV.call.to_sym)
       ENV["VERBOSE"] = old
     end
   end

activerecord/test/cases/connection_adapters/connection_handler_test.rb

@@ -385,8 +385,8 @@ def test_pool_from_any_process_for_uses_most_recent_spec
           wr.binmode
 
           pid = fork do
-            ActiveRecord::Base.configurations["arunit"]["database"] = file.path
-            ActiveRecord::Base.establish_connection(:arunit)
+            config_hash = ActiveRecord::Base.configurations.configs_for(env_name: "arunit", spec_name: "primary").configuration_hash.merge(database: file.path)
+            ActiveRecord::Base.establish_connection(config_hash)
 
             pid2 = fork do
               wr.write ActiveRecord::Base.connection_db_config.database

activerecord/test/cases/connection_pool_test.rb

@@ -200,8 +200,11 @@ def test_reap_inactive
 
       def test_idle_timeout_configuration
         @pool.disconnect!
-        @db_config.configuration_hash.merge!(idle_timeout: "0.02")
-        pool_config = ActiveRecord::ConnectionAdapters::PoolConfig.new("primary", @db_config)
+
+        config = @db_config.configuration_hash.merge(idle_timeout: "0.02")
+        db_config = ActiveRecord::DatabaseConfigurations::HashConfig.new(@db_config.env_name, @db_config.spec_name, config)
+
+        pool_config = ActiveRecord::ConnectionAdapters::PoolConfig.new("primary", db_config)
         @pool = ConnectionPool.new(pool_config)
         idle_conn = @pool.checkout
         @pool.checkin(idle_conn)
@@ -225,8 +228,10 @@ def test_idle_timeout_configuration
 
       def test_disable_flush
         @pool.disconnect!
-        @db_config.configuration_hash.merge!(idle_timeout: -5)
-        pool_config = ActiveRecord::ConnectionAdapters::PoolConfig.new("primary", @db_config)
+
+        config = @db_config.configuration_hash.merge(idle_timeout: -5)
+        db_config = ActiveRecord::DatabaseConfigurations::HashConfig.new(@db_config.env_name, @db_config.spec_name, config)
+        pool_config = ActiveRecord::ConnectionAdapters::PoolConfig.new("primary", db_config)
         @pool = ConnectionPool.new(pool_config)
         idle_conn = @pool.checkout
         @pool.checkin(idle_conn)
@@ -720,12 +725,10 @@ def test_public_connections_access_threadsafe
 
       private
         def with_single_connection_pool
-          old_config = @db_config.configuration_hash
-          db_config = ActiveRecord::DatabaseConfigurations::HashConfig.new("arunit", "primary", old_config.dup)
-
-          db_config.configuration_hash[:pool] = 1 # this is safe to do, because .dupped PoolConfig also auto-dups its config
-
+          config = @db_config.configuration_hash.merge(pool: 1)
+          db_config = ActiveRecord::DatabaseConfigurations::HashConfig.new("arunit", "primary", config)
           pool_config = ActiveRecord::ConnectionAdapters::PoolConfig.new("primary", db_config)
+
           yield(pool = ConnectionPool.new(pool_config))
         ensure
           pool.disconnect! if pool

activerecord/test/cases/reaper_test.rb

@@ -68,9 +68,7 @@ def test_pool_has_reaper
       end
 
       def test_reaping_frequency_configuration
-        pool_config = duplicated_pool_config
-        pool_config.db_config.configuration_hash[:reaping_frequency] = "10.01"
-
+        pool_config = duplicated_pool_config(reaping_frequency: "10.01")
         pool = ConnectionPool.new(pool_config)
 
         assert_equal 10.01, pool.reaper.frequency
@@ -79,9 +77,7 @@ def test_reaping_frequency_configuration
       end
 
       def test_connection_pool_starts_reaper
-        pool_config = duplicated_pool_config
-        pool_config.db_config.configuration_hash[:reaping_frequency] = "0.0001"
-
+        pool_config = duplicated_pool_config(reaping_frequency: "0.0001")
         pool = ConnectionPool.new(pool_config)
 
         conn, child = new_conn_in_thread(pool)
@@ -97,8 +93,7 @@ def test_connection_pool_starts_reaper
       end
 
       def test_reaper_works_after_pool_discard
-        pool_config = duplicated_pool_config
-        pool_config.db_config.configuration_hash[:reaping_frequency] = "0.0001"
+        pool_config = duplicated_pool_config(reaping_frequency: "0.0001")
 
         2.times do
           pool = ConnectionPool.new(pool_config)
@@ -129,9 +124,7 @@ def test_reap_flush_on_discarded_pool
 
       if Process.respond_to?(:fork)
         def test_connection_pool_starts_reaper_in_fork
-          pool_config = duplicated_pool_config
-          pool_config.db_config.configuration_hash[:reaping_frequency] = "0.0001"
-
+          pool_config = duplicated_pool_config(reaping_frequency: "0.0001")
           pool = ConnectionPool.new(pool_config)
           pool.checkout
 
@@ -175,8 +168,8 @@ def test_reaper_does_not_reap_discarded_connection_pools
       end
 
       private
-        def duplicated_pool_config
-          old_config = ActiveRecord::Base.connection_pool.db_config.configuration_hash
+        def duplicated_pool_config(merge_config_options = {})
+          old_config = ActiveRecord::Base.connection_pool.db_config.configuration_hash.merge(merge_config_options)
           db_config = ActiveRecord::DatabaseConfigurations::HashConfig.new("arunit", "primary", old_config.dup)
           PoolConfig.new("primary", db_config)
         end

activerecord/test/cases/test_databases_test.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+class TestDatabasesTest < ActiveRecord::TestCase
+  unless in_memory_db?
+    def test_databases_are_created
+      previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "arunit"
+
+      base_db_config = ActiveRecord::Base.configurations.configs_for(env_name: "arunit", spec_name: "primary")
+      expected_database = "#{base_db_config.database}-2"
+
+      ActiveRecord::Tasks::DatabaseTasks.stub(:reconstruct_from_schema, ->(db_config, _, _) {
+        assert_equal expected_database, db_config.database
+      }) do
+        ActiveRecord::TestDatabases.create_and_load_schema(2, env_name: "arunit")
+      end
+    ensure
+      ENV["RAILS_ENV"] = previous_env
+    end
+  end
+end