Extract internal ActiveSupport::ConfigurationFile object

Rails has a number of places where a YAML configuration file is read,
then ERB is evaluated and finally the YAML is parsed.

This consolidates that into one common class.

Co-authored-by: Kasper Timm Hansen <kaspth@gmail.com>

activerecord/lib/active_record/fixture_set/file.rb

@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
-require "erb"
-require "yaml"
+require "active_support/configuration_file"
 
 module ActiveRecord
   class FixtureSet
@@ -51,24 +50,14 @@ def config_row
 
         def raw_rows
           @raw_rows ||= begin
-            data = YAML.load(render(IO.read(@file)))
+            data = ActiveSupport::ConfigurationFile.parse(@file, context:
+              ActiveRecord::FixtureSet::RenderContext.create_subclass.new.get_binding)
             data ? validate(data).to_a : []
-          rescue ArgumentError, Psych::SyntaxError => error
-            raise Fixture::FormatError, "a YAML error occurred parsing #{@file}. Please note that YAML must be consistently indented using spaces. Tabs are not allowed. Please have a look at https://www.yaml.org/faq.html\nThe exact error was:\n  #{error.class}: #{error}", error.backtrace
+          rescue RuntimeError => error
+            raise Fixture::FormatError, error.message
           end
         end
 
-        def prepare_erb(content)
-          erb = ERB.new(content)
-          erb.filename = @file
-          erb
-        end
-
-        def render(content)
-          context = ActiveRecord::FixtureSet::RenderContext.create_subclass.new
-          prepare_erb(content).result(context.get_binding)
-        end
-
         # Validate our unmarshalled data.
         def validate(data)
           unless Hash === data || YAML::Omap === data

activerecord/lib/active_record/railties/databases.rake

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "active_record"
+require "active_support/configuration_file"
 
 databases = ActiveRecord::Tasks::DatabaseTasks.setup_initial_database_yaml
 
@@ -369,7 +370,7 @@ db_namespace = namespace :db do
       base_dir = ActiveRecord::Tasks::DatabaseTasks.fixtures_path
 
       Dir["#{base_dir}/**/*.yml"].each do |file|
-        if data = YAML.load(ERB.new(IO.read(file)).result)
+        if data = ActiveSupport::ConfigurationFile.parse(file)
           data.each_key do |key|
             key_id = ActiveRecord::FixtureSet.identify(key)
 

activerecord/test/cases/fixture_set/file_test.rb

@@ -137,12 +137,6 @@ def test_extracts_model_class_from_config_row
         end
       end
 
-      def test_erb_filename
-        filename = "filename.yaml"
-        erb = File.new(filename).send(:prepare_erb, "<% Rails.env %>\n")
-        assert_equal erb.filename, filename
-      end
-
       private
         def tmp_yaml(name, contents)
           t = Tempfile.new name

activerecord/test/support/config.rb

@@ -1,9 +1,8 @@
 # frozen_string_literal: true
 
-require "yaml"
-require "erb"
 require "fileutils"
 require "pathname"
+require "active_support/configuration_file"
 
 module ARTest
   class << self
@@ -21,8 +20,7 @@ def read_config
           FileUtils.cp TEST_ROOT + "/config.example.yml", config_file
         end
 
-        erb = ERB.new(config_file.read)
-        expand_config(YAML.parse(erb.result(binding)).transform)
+        expand_config ActiveSupport::ConfigurationFile.parse(config_file)
       end
 
       def expand_config(config)

activestorage/lib/active_storage/engine.rb

@@ -106,17 +106,10 @@ class Engine < Rails::Engine # :nodoc:
       ActiveSupport.on_load(:active_storage_blob) do
         configs = Rails.configuration.active_storage.service_configurations ||=
           begin
-            config_file = Pathname.new(Rails.root.join("config/storage.yml"))
+            config_file = Rails.root.join("config/storage.yml")
             raise("Couldn't find Active Storage configuration in #{config_file}") unless config_file.exist?
 
-            require "yaml"
-            require "erb"
-
-            YAML.load(ERB.new(config_file.read).result) || {}
-          rescue Psych::SyntaxError => e
-            raise "YAML syntax error occurred while parsing #{config_file}. " \
-                  "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
-                  "Error: #{e.message}"
+            ActiveSupport::ConfigurationFile.parse(config_file)
           end
 
         ActiveStorage::Blob.services = ActiveStorage::Service::Registry.new(configs)

activestorage/test/test_helper.rb

@@ -8,6 +8,7 @@
 require "active_support/test_case"
 require "active_support/core_ext/object/try"
 require "active_support/testing/autorun"
+require "active_support/configuration_file"
 require "active_storage/service/mirror_service"
 require "image_processing/mini_magick"
 
@@ -23,11 +24,8 @@
 # Filter out the backtrace from minitest while preserving the one from other libraries.
 Minitest.backtrace_filter = Minitest::BacktraceFilter.new
 
-require "yaml"
 SERVICE_CONFIGURATIONS = begin
-  erb = ERB.new(Pathname.new(File.expand_path("service/configurations.yml", __dir__)).read)
-  configuration = YAML.load(erb.result) || {}
-  configuration.deep_symbolize_keys
+  ActiveSupport::ConfigurationFile.parse(File.expand_path("service/configurations.yml", __dir__)).deep_symbolize_keys
 rescue Errno::ENOENT
   puts "Missing service configuration file in test/service/configurations.yml"
   {}

activesupport/lib/active_support.rb

@@ -35,6 +35,7 @@ module ActiveSupport
 
   autoload :Concern
   autoload :ActionableError
+  autoload :ConfigurationFile
   autoload :CurrentAttributes
   autoload :Dependencies
   autoload :DescendantsTracker

activesupport/lib/active_support/configuration_file.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module ActiveSupport
+  # Reads a YAML configuration file, evaluating any ERB, then
+  # parsing the resulting YAML.
+  #
+  # Warns in case of YAML confusing characters, like invisible
+  # non-breaking spaces.
+  class ConfigurationFile # :nodoc:
+    class FormatError < StandardError; end
+
+    def initialize(content_path)
+      @content_path = content_path
+      @content = read content_path
+    end
+
+    def self.parse(content_path, **options)
+      new(content_path).parse(**options)
+    end
+
+    def parse(context: nil, **options)
+      yaml = context ? ERB.new(@content).result(context) : ERB.new(@content).result
+      YAML.load(yaml, **options) || {}
+    rescue Psych::SyntaxError => error
+      raise "YAML syntax error occurred while parsing #{@content_path}. " \
+            "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
+            "Error: #{error.message}"
+    end
+
+    private
+      def read(content_path)
+        require "yaml"
+        require "erb"
+
+        File.read(content_path).tap do |content|
+          if content.match?(/\U+A0/)
+            warn "File contains invisible non-breaking spaces, you may want to remove those"
+          end
+        end
+      end
+  end
+end

railties/lib/rails/application.rb

@@ -8,6 +8,7 @@
 require "active_support/encrypted_configuration"
 require "active_support/deprecation"
 require "active_support/hash_with_indifferent_access"
+require "active_support/configuration_file"
 require "rails/engine"
 require "rails/secrets"
 
@@ -224,7 +225,7 @@ def config_for(name, env: Rails.env)
 
       if yaml.exist?
         require "erb"
-        all_configs    = YAML.load(ERB.new(yaml.read).result, symbolize_names: true) || {}
+        all_configs    = ActiveSupport::ConfigurationFile.parse(yaml, symbolize_names: true)
         config, shared = all_configs[env.to_sym], all_configs[:shared]
 
         if config.is_a?(Hash)
@@ -235,10 +236,6 @@ def config_for(name, env: Rails.env)
       else
         raise "Could not load configuration. No such file - #{yaml}"
       end
-    rescue Psych::SyntaxError => error
-      raise "YAML syntax error occurred while parsing #{yaml}. " \
-        "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
-        "Error: #{error.message}"
     end
 
     # Stores some of the Rails initial environment parameters which

railties/lib/rails/application/configuration.rb

@@ -3,6 +3,7 @@
 require "ipaddr"
 require "active_support/core_ext/kernel/reporting"
 require "active_support/file_update_checker"
+require "active_support/configuration_file"
 require "rails/engine/configuration"
 require "rails/source_annotation_extractor"
 
@@ -247,12 +248,9 @@ def database_configuration
         path = paths["config/database"].existent.first
         yaml = Pathname.new(path) if path
 
-        config = if yaml && yaml.exist?
-          require "yaml"
-          require "erb"
-          loaded_yaml = YAML.load(ERB.new(yaml.read).result) || {}
-          shared = loaded_yaml.delete("shared")
-          if shared
+        config = if yaml&.exist?
+          loaded_yaml = ActiveSupport::ConfigurationFile.parse(yaml)
+          if (shared = loaded_yaml.delete("shared"))
             loaded_yaml.each do |_k, values|
               values.reverse_merge!(shared)
             end
@@ -267,10 +265,6 @@ def database_configuration
         end
 
         config
-      rescue Psych::SyntaxError => e
-        raise "YAML syntax error occurred while parsing #{paths["config/database"].first}. " \
-              "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
-              "Error: #{e.message}"
       rescue => e
         raise e, "Cannot load database configuration:\n#{e.message}", e.backtrace
       end