Add better return type for preg_split

stubs/CoreGenericFunctions.phpstub

@@ -602,6 +602,17 @@ function implode($glue, array $pieces = []) : string {}
  */
 function explode(string $delimiter, string $string, int $limit = -1) : array {}
 
+/**
+ * @psalm-pure
+ *
+ * @psalm-flow ($subject) -(array-assignment)-> return
+ *
+ * @return ($flags is 1|3|5|7 ? list<string>|false : non-empty-list<string>|false)
+ *
+ * @psalm-ignore-falsable-return
+ */
+function preg_split(string $pattern, string $subject, int $limit = -1, int $flags = 0) {}
+
 /**
  * @param array $input
  *

tests/FunctionCallTest.php

@@ -1355,6 +1355,13 @@ class FunctionCallTest extends TestCase
                 [],
                 '7.4'
             ],
+            'pregSplit' => [
+                '<?php
+                    /** @return non-empty-list */
+                    function foo(string $s) {
+                        return preg_split("/ /", $s);
+                    }'
+            ],
         ];
     }
 
@@ -1856,6 +1863,14 @@ class FunctionCallTest extends TestCase
                     }',
                 'error_message' => 'ArgumentTypeCoercion',
             ],
+            'pregSplitNoEmpty' => [
+                '<?php
+                    /** @return non-empty-list */
+                    function foo(string $s) {
+                        return preg_split("/ /", $s, -1, PREG_SPLIT_NO_EMPTY);
+                    }',
+                'error_message' => 'InvalidReturnStatement'
+            ],
         ];
     }
 }