Tell the user which file is missing when config/database.yml was not found

Since cc03675d30b58e28f585720dad14e947a57ff5b the error message became like
"Could not load database configuration. No such file -"
which doesn't really tell what's actually missing.

railties/lib/rails/application/configuration.rb

@@ -93,9 +93,10 @@ def paths
       # Loads and returns the entire raw configuration of database from
       # values stored in `config/database.yml`.
       def database_configuration
-        yaml = Pathname.new(paths["config/database"].existent.first || "")
+        path = paths["config/database"].existent.first
+        yaml = Pathname.new(path) if path
 
-        config = if yaml.exist?
+        config = if yaml && yaml.exist?
           require "yaml"
           require "erb"
           YAML.load(ERB.new(yaml.read).result) || {}
@@ -104,7 +105,7 @@ def database_configuration
           # by Active Record.
           {}
         else
-          raise "Could not load database configuration. No such file - #{yaml}"
+          raise "Could not load database configuration. No such file - #{paths["config/database"].instance_variable_get(:@paths)}"
         end
 
         config

railties/test/application/configuration_test.rb

@@ -980,6 +980,15 @@ def index
       assert_kind_of Hash, Rails.application.config.database_configuration
     end
 
+    test 'raises with proper error message if no database configuration found' do
+      FileUtils.rm("#{app_path}/config/database.yml")
+      require "#{app_path}/config/environment"
+      err = assert_raises RuntimeError do
+        Rails.application.config.database_configuration
+      end
+      assert_match 'config/database', err.message
+    end
+
     test 'config.action_mailer.show_previews defaults to true in development' do
       Rails.env = "development"
       require "#{app_path}/config/environment"