Only merge DATABASE_URL settings into the current env

This commit fixes a regression where when the `DATABASE_URL` environment
variable was set and the current Rails environment had a valid configuration
defined in the database config, settings from the environment variable would
affect _all_ environments (not just the current one).

activerecord/lib/active_record/database_configurations.rb

@@ -105,18 +105,20 @@ def build_configs(configs)
         return configs if configs.is_a?(Array)
 
         db_configs = configs.flat_map do |env_name, config|
-          if config.is_a?(Hash) && config.all? { |k, v| v.is_a?(Hash) }
+          if config.is_a?(Hash) && config.all? { |_, v| v.is_a?(Hash) }
             walk_configs(env_name.to_s, config)
           else
             build_db_config_from_raw_config(env_name.to_s, "primary", config)
           end
-        end.compact
+        end
 
-        if url = ENV["DATABASE_URL"]
-          merge_url_with_configs(url, db_configs)
-        else
-          db_configs
+        current_env = ActiveRecord::ConnectionHandling::DEFAULT_ENV.call.to_s
+
+        unless db_configs.find(&:for_current_env?)
+          db_configs << environment_url_config(current_env, "primary", {})
         end
+
+        merge_db_environment_variables(current_env, db_configs.compact)
       end
 
       def walk_configs(env_name, config)
@@ -156,22 +158,22 @@ def build_db_config_from_hash(env_name, spec_name, config)
         end
       end
 
-      def merge_url_with_configs(url, configs)
-        env = ActiveRecord::ConnectionHandling::DEFAULT_ENV.call.to_s
+      def merge_db_environment_variables(current_env, configs)
+        configs.map do |config|
+          next config if config.url_config? || config.env_name != current_env
 
-        if configs.find(&:for_current_env?)
-          configs.map do |config|
-            if config.url_config?
-              config
-            else
-              ActiveRecord::DatabaseConfigurations::UrlConfig.new(config.env_name, config.spec_name, url, config.config)
-            end
-          end
-        else
-          configs + [ActiveRecord::DatabaseConfigurations::UrlConfig.new(env, "primary", url)]
+          url_config = environment_url_config(current_env, config.spec_name, config.config)
+          url_config || config
         end
       end
 
+      def environment_url_config(env, spec_name, config)
+        url = ENV["DATABASE_URL"]
+        return unless url
+
+        ActiveRecord::DatabaseConfigurations::UrlConfig.new(env, spec_name, url, config)
+      end
+
       def method_missing(method, *args, &blk)
         case method
         when :each, :first

activerecord/test/cases/connection_adapters/merge_and_resolve_default_url_config_test.rb

@@ -347,6 +347,22 @@ def test_tiered_configs_with_database_url
           assert_equal expected, actual
         end
       end
+
+      def test_does_not_change_other_environments
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
+        config = { "production" => { "adapter" => "not_postgres", "database" => "not_foo", "host" => "localhost" }, "default_env" => {} }
+
+        actual = resolve_spec(:production, config)
+        assert_equal config["production"].merge("name" => "production"), actual
+
+        actual = resolve_spec(:default_env, config)
+        assert_equal({
+          "host" => "localhost",
+          "database" => "foo",
+          "adapter" => "postgresql",
+          "name" => "default_env"
+        }, actual)
+      end
     end
   end
 end