Compile has a message to tell.

bin/compile

@@ -5,5 +5,7 @@ require __DIR__.'/../src/bootstrap.php';
 
 use Composer\Compiler;
 
+error_reporting(~0); ini_set('display_errors', 1);
+
 $compiler = new Compiler();
 $compiler->compile();

bin/composer

@@ -5,6 +5,8 @@ require __DIR__.'/../src/bootstrap.php';
 
 use Composer\Console\Application;
 
+error_reporting(~0); ini_set('display_errors', 1);
+
 // run the command application
 $application = new Application();
 $application->run();