Fix #3521 version mismatch when running diag, Replaced git command to get current checked out tag

src/Composer/Compiler.php

@@ -55,9 +55,12 @@ class Compiler
         $date->setTimezone(new \DateTimeZone('UTC'));
         $this->versionDate = $date->format('Y-m-d H:i:s');
 
-        $process = new Process('git describe --tags HEAD');
+        $process = new Process('git name-rev --tags --name-only $(git rev-parse HEAD)');
         if ($process->run() == 0) {
-            $this->version = trim($process->getOutput());
+            $output = trim($process->getOutput());
+            if ($output != 'undefined') {
+                $this->version = $output;
+            }
         } else {
             // get branch-alias defined in composer.json for dev-master (if any)
             $localConfig = __DIR__.'/../../composer.json';