Don't require -o arg when running autogen (GoogleCloudPlatform#11474)

mmv1/compiler.rb

@@ -105,7 +105,8 @@
   if products_to_generate && all_products
 raise 'Either -p/--products OR -a/--all must be present' \
   if products_to_generate.nil? && !all_products
-raise 'Option -o/--output is a required parameter' if output_path.nil?
+raise 'Option -o/--output is a required parameter' \
+  if output_path.nil? && !openapi_generate
 raise 'Option -e/--engine is a required parameter' if provider_name.nil?
 
 if openapi_generate

mmv1/openapi_generate/parser.rb

@@ -25,7 +25,10 @@ def initialize(folder, output)
     end
 
     def run
-      Dir[@folder].each do |openapi_file|
+      openapi_dir = Dir[@folder]
+      raise "No OpenAPI files found in #{@folder}" if openapi_dir.empty?
+
+      openapi_dir.each do |openapi_file|
         write_yaml(openapi_file, @output)
       end
     end
@@ -287,10 +290,12 @@ def build_product(spec_path, output)
     def write_yaml(spec_path, output)
       resource_paths = find_resources(spec_path)
       product_path = build_product(spec_path, output)
+      Google::LOGGER.info "Generated product '#{product_path}/product.yaml'"
       resource_paths.each do |path_array|
         resource = build_resource(spec_path, path_array[0], path_array[1])
         file_path = File.join(product_path, "#{resource.name}.yaml")
         File.write(file_path, resource.to_yaml)
+        Google::LOGGER.info "Generated resource '#{file_path}'"
       end
     end
   end