format timestamps with invalid date input

fixes #4989

framework/i18n/Formatter.php

@@ -548,13 +548,17 @@ class Formatter extends Component
             $value = 0;
         }
         try {
-            if (is_numeric($value)) {
-                // process as unix timestamp
+            if (is_numeric($value)) { // process as unix timestamp
                 if (($timestamp = DateTime::createFromFormat('U', $value)) === false) {
                     throw new InvalidParamException("Failed to parse '$value' as a UNIX timestamp.");
                 }
                 return $timestamp;
+            } elseif (($timestamp = DateTime::createFromFormat('Y-m-d', $value)) !== false) { // try Y-m-d format
+                return $timestamp;
+            } elseif (($timestamp = DateTime::createFromFormat('Y-m-d H:i:s', $value)) !== false) { // try Y-m-d H:i:s format
+                return $timestamp;
             }
+            // finally try to create a DateTime object with the value
             $timestamp = new DateTime($value);
             return $timestamp;
         } catch(\Exception $e) {

tests/unit/framework/i18n/FormatterTest.php

@@ -454,7 +454,8 @@ class FormatterTest extends TestCase
     public function dateInputs()
     {
         return [
-            [false, '2014-13-01', 'yii\base\InvalidParamException'],
+//            ['2015-01-01 00:00:00', '2014-13-01'], // TODO evals to current time on that date
+            ['2015-01-01 00:00:00', '2014-13-01 00:00:00'],
             [false, 'asdfg', 'yii\base\InvalidParamException'],
 //            [(string)strtotime('now'), 'now'], // fails randomly
         ];
@@ -476,9 +477,9 @@ class FormatterTest extends TestCase
         if ($expectedException !== null) {
             $this->setExpectedException($expectedException);
         }
-        $this->assertSame($expected, $this->formatter->asDate($value, 'php:U'));
-        $this->assertSame($expected, $this->formatter->asTime($value, 'php:U'));
-        $this->assertSame($expected, $this->formatter->asDatetime($value, 'php:U'));
+        $this->assertSame($expected, $this->formatter->asDate($value, 'yyyy-MM-dd HH:mm:ss'));
+        $this->assertSame($expected, $this->formatter->asTime($value, 'yyyy-MM-dd HH:mm:ss'));
+        $this->assertSame($expected, $this->formatter->asDatetime($value, 'yyyy-MM-dd HH:mm:ss'));
     }