prometheus order for metric without labels fix

Author: nekufa

src/Metrics/Exporter/PrometheusExporter.php

@@ -35,7 +35,7 @@ public function toString(string $prefix = '', array $labels = []): string
                 $key .= '{' . implode(',', $rowLabels) . '}';
             }
 
-            $result[$key] = sprintf('%s %s', $key, $row['value']);
+            $result[$key . '_'] = sprintf('%s %s', $key, $row['value']);
         }
 
         ksort($result);

tests/Metrics/ExporterTest.php

@@ -87,17 +87,22 @@ public function testMetricsOrder()
         $registry->set('todo', 1, ['queue' => 'web.bundle']);
         $registry->set('complete', 2, ['queue' => 'flow.promote']);
         $registry->set('todo', 3, ['queue' => 'space.housekeeping']);
+        $registry->set('counter', 1);
 
         $info = new Info();
         $info->set('todo', 'waiting');
         $info->set('complete', 'complete');
+        $info->set('counter', 'example');
 
         $string = (new PrometheusExporter($registry, $info))->toString();
 
         $shouldbe = implode(PHP_EOL, [
             '# HELP complete complete',
             '# TYPE complete gauge',
             'complete{queue="flow.promote"} 2',
+            '# HELP counter example',
+            '# TYPE counter gauge',
+            'counter 1',
             '# HELP todo waiting',
             '# TYPE todo gauge',
             'todo{queue="space.housekeeping"} 3',