From b229ac875dcd00b3442cc3b40792482b483f8e5d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pavel=20Bate=C4=8Dko?= <ShiraNai7@users.noreply.github.com>
Date: Sat, 2 Nov 2019 10:10:38 +0100
Subject: [PATCH] Improve return types of explode() with limit (#2286)

---
 .../Internal/Analyzer/FunctionAnalyzer.php    | 16 +++-
 tests/FunctionCallTest.php                    | 92 +++++++++++++++++--
 2 files changed, 96 insertions(+), 12 deletions(-)

diff --git a/src/Psalm/Internal/Analyzer/FunctionAnalyzer.php b/src/Psalm/Internal/Analyzer/FunctionAnalyzer.php
index 707910f80..2b2563582 100644
--- a/src/Psalm/Internal/Analyzer/FunctionAnalyzer.php
+++ b/src/Psalm/Internal/Analyzer/FunctionAnalyzer.php
@@ -249,20 +249,30 @@ class FunctionAnalyzer extends FunctionLikeAnalyzer
                     break;
 
                 case 'explode':
-                    if (count($call_args) === 2) {
+                    if (count($call_args) >= 2) {
+                        $can_return_empty = isset($call_args[2])
+                            && (
+                                !$call_args[2]->value instanceof PhpParser\Node\Scalar\LNumber
+                                || $call_args[2]->value->value < 0
+                            );
+
                         if ($call_args[0]->value instanceof PhpParser\Node\Scalar\String_) {
                             if ($call_args[0]->value->value === '') {
                                 return Type::getFalse();
                             }
 
                             return new Type\Union([
-                                new Type\Atomic\TNonEmptyList(Type::getString())
+                                $can_return_empty
+                                    ? new Type\Atomic\TList(Type::getString())
+                                    : new Type\Atomic\TNonEmptyList(Type::getString())
                             ]);
                         } elseif (isset($call_args[0]->value->inferredType)
                             && $call_args[0]->value->inferredType->hasString()
                         ) {
                             $falsable_array = new Type\Union([
-                                new Type\Atomic\TNonEmptyList(Type::getString()),
+                                $can_return_empty
+                                    ? new Type\Atomic\TList(Type::getString())
+                                    : new Type\Atomic\TNonEmptyList(Type::getString()),
                                 new Type\Atomic\TFalse
                             ]);
 
diff --git a/tests/FunctionCallTest.php b/tests/FunctionCallTest.php
index 1787ef9ca..bd06e4fb1 100644
--- a/tests/FunctionCallTest.php
+++ b/tests/FunctionCallTest.php
@@ -945,19 +945,93 @@ class FunctionCallTest extends TestCase
                     '$c' => 'int',
                 ],
             ],
+            'explode' => [
+                '<?php
+                    /** @var string $string */
+                    $elements = explode(" ", $string);',
+                'assertions' => [
+                    '$elements' => 'non-empty-list<string>',
+                ],
+            ],
+            'explodeWithPositiveLimit' => [
+                '<?php
+                    /** @var string $string */
+                    $elements = explode(" ", $string, 5);',
+                'assertions' => [
+                    '$elements' => 'non-empty-list<string>',
+                ],
+            ],
+            'explodeWithNegativeLimit' => [
+                '<?php
+                    /** @var string $string */
+                    $elements = explode(" ", $string, -5);',
+                'assertions' => [
+                    '$elements' => 'list<string>',
+                ],
+            ],
+            'explodeWithDynamicLimit' => [
+                '<?php
+                    /**
+                     * @var string $string
+                     * @var int $limit
+                     */
+                    $elements = explode(" ", $string, $limit);',
+                'assertions' => [
+                    '$elements' => 'list<string>',
+                ],
+            ],
+            'explodeWithDynamicDelimiter' => [
+                '<?php
+                    /**
+                     * @var string $delim
+                     * @var string $string
+                     */
+                    $elements = explode($delim, $string);',
+                'assertions' => [
+                    '$elements' => 'false|non-empty-list<string>',
+                ],
+            ],
+            'explodeWithDynamicDelimiterAndPositiveLimit' => [
+                '<?php
+                    /**
+                     * @var string $delim
+                     * @var string $string
+                     */
+                    $elements = explode($delim, $string, 5);',
+                'assertions' => [
+                    '$elements' => 'false|non-empty-list<string>',
+                ],
+            ],
+            'explodeWithDynamicDelimiterAndNegativeLimit' => [
+                '<?php
+                    /**
+                     * @var string $delim
+                     * @var string $string
+                     */
+                    $elements = explode($delim, $string, -5);',
+                'assertions' => [
+                    '$elements' => 'false|list<string>',
+                ],
+            ],
+            'explodeWithDynamicDelimiterAndLimit' => [
+                '<?php
+                    /**
+                     * @var string $delim
+                     * @var string $string
+                     * @var int $limit
+                     */
+                    $elements = explode($delim, $string, $limit);',
+                'assertions' => [
+                    '$elements' => 'false|list<string>',
+                ],
+            ],
             'explodeWithPossiblyFalse' => [
                 '<?php
-                    /** @return array<int, string> */
-                    function exploder(string $s) : array {
-                        return explode(" ", $s);
+                    /** @return non-empty-list<string> */
+                    function exploder(string $d, string $s) : array {
+                        return explode($d, $s);
                     }',
             ],
-            'explodeWithThirdArg' => [
-                '<?php
-                    $elements = explode("_", "", -1);
-                    $element = array_shift($elements);
-                    assert(null !== $element);'
-            ],
             'allowPossiblyUndefinedClassInClassExists' => [
                 '<?php
                     if (class_exists(Foo::class)) {}',