Merge branch '1.x', fixes #771

src/Monolog/Handler/RotatingFileHandler.php

@@ -69,7 +69,7 @@ class RotatingFileHandler extends StreamHandler
 
     public function setFilenameFormat($filenameFormat, $dateFormat)
     {
-        if (!preg_match('{^Y(([/_.-]m)([/_.-]d)?)?$}', $dateFormat)) {
+        if (!preg_match('{^Y(([/_.-]?m)([/_.-]?d)?)?$}', $dateFormat)) {
             throw new InvalidArgumentException(
                 'Invalid date format - format must be one of '.
                 'RotatingFileHandler::FILE_PER_DAY ("Y-m-d"), RotatingFileHandler::FILE_PER_MONTH ("Y-m")'.

tests/Monolog/Handler/RotatingFileHandlerTest.php

@@ -156,9 +156,13 @@ class RotatingFileHandlerTest extends TestCase
             ['Y/m/d', true],
             ['Y.m.d', true],
             ['Y_m_d', true],
+            ['Ymd', true],
+            ['Ym/d', true],
             ['Y/m', true],
+            ['Ym', true],
             ['Y.m', true],
             ['Y_m', true],
+            ['Y/md', true],
             ['', false],
             ['m-d-Y', false],
             ['Y-m-d-h-i', false],