Warn when init is being used non-interactively without any args passed in, instead of silently overwriting the file

src/Composer/Command/InitCommand.php

@@ -129,6 +129,12 @@ EOT
 
                 return 1;
             }
+        } else {
+            if (json_encode($options) === '{"require":{}}') {
+                throw new \RuntimeException('You have to run this command in interactive mode, or specify at least some data using --name, --require, etc.');
+            }
+
+            $io->writeError('Writing composer.json');
         }
 
         $file->write($options);