Improve output of --check-version CLI option

Author: sebastianbergmann

src/TextUI/Command.php

@@ -1142,17 +1142,31 @@ protected function handleVersionCheck(): void
     {
         $this->printVersionString();
 
-        $latestVersion = file_get_contents('https://phar.phpunit.de/latest-version-of/phpunit');
-        $isOutdated    = version_compare($latestVersion, Version::id(), '>');
+        $latestVersion           = file_get_contents('https://phar.phpunit.de/latest-version-of/phpunit');
+        $latestCompatibleVersion = file_get_contents('https://phar.phpunit.de/latest-version-of/phpunit-' . explode('.', Version::series())[0]);
 
-        if ($isOutdated) {
+        $notLatest           = version_compare($latestVersion, Version::id(), '>');
+        $notLatestCompatible = version_compare($latestCompatibleVersion, Version::id(), '>');
+
+        if ($notLatest || $notLatestCompatible) {
+            print 'You are not using the latest version of PHPUnit.' . PHP_EOL;
+        } else {
+            print 'You are using the latest version of PHPUnit.' . PHP_EOL;
+        }
+
+        if ($notLatestCompatible) {
+            printf(
+                'The latest version compatible with PHPUnit %s is PHPUnit %s.' . PHP_EOL,
+                Version::id(),
+                $latestCompatibleVersion
+            );
+        }
+
+        if ($notLatest) {
             printf(
-                'You are not using the latest version of PHPUnit.' . PHP_EOL .
                 'The latest version is PHPUnit %s.' . PHP_EOL,
                 $latestVersion
             );
-        } else {
-            print 'You are using the latest version of PHPUnit.' . PHP_EOL;
         }
 
         exit(TestRunner::SUCCESS_EXIT);