From 88d8d9903bd0224757db2b78a69d88d2ad4f1adb Mon Sep 17 00:00:00 2001
From: PurHur <PurHur@users.noreply.github.com>
Date: Fri, 17 Jul 2026 07:46:34 +0000
Subject: [PATCH] =?UTF-8?q?Implement=20mb=5Fstrstr()=20=E2=80=94=20multiby?=
 =?UTF-8?q?te=20strstr=20parity=20with=20ext/mbstring?=
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Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Closes #19941

Adds mb_strstr($haystack, $needle, $before_needle, $encoding) to the
VM via VmMbstring::strstr() using the existing utf8Strpos + utf8CharSubstr
helpers. Registered in ext/mbstring/Module.php alongside mb_strrichr.

Verification: php bin/vm.php repro.php — output matches Zend PHP 8.2
  phpunit --filter mb_strstr — OK (2 tests, VM + JIT)
  phpunit --filter mb_str — OK (40 tests, no regressions)
Co-authored-by: Cursor <cursoragent@cursor.com>
---
 ext/mbstring/Module.php                     |  1 +
 ext/mbstring/VmMbstring.php                 | 20 ++++++
 ext/mbstring/mb_strstr.php                  | 76 +++++++++++++++++++++
 test/compliance/cases/stdlib/mb_strstr.phpt | 15 ++++
 4 files changed, 112 insertions(+)
 create mode 100644 ext/mbstring/mb_strstr.php
 create mode 100644 test/compliance/cases/stdlib/mb_strstr.phpt

diff --git a/ext/mbstring/Module.php b/ext/mbstring/Module.php
index ebab648f947..0da76fb397c 100644
--- a/ext/mbstring/Module.php
+++ b/ext/mbstring/Module.php
@@ -53,6 +53,7 @@ public function getFunctions(): array
             new mb_stripos(),
             new mb_strrpos(),
             new mb_strrichr(),
+            new mb_strstr(),
             ...(CompilerVersion::supportsMbTrimFunctions() ? [
                 new mb_trim(),
                 new mb_ltrim(),
diff --git a/ext/mbstring/VmMbstring.php b/ext/mbstring/VmMbstring.php
index 30d3c4291a8..c07a4f511d7 100644
--- a/ext/mbstring/VmMbstring.php
+++ b/ext/mbstring/VmMbstring.php
@@ -542,6 +542,26 @@ public static function strpos(string $haystack, string $needle, int $offset = 0,
         return self::utf8Strpos($haystack, $needle, $offset, false, $encoding, 'mb_strpos');
     }
 
+    /**
+     * mb_strstr() — find first occurrence and return haystack from that point (php-src ext/mbstring/mbstring.c).
+     *
+     * @return string|false
+     */
+    public static function strstr(string $haystack, string $needle, bool $part = false, string $encoding = 'UTF-8')
+    {
+        self::assertSearchEncoding($encoding);
+        $pos = self::utf8Strpos($haystack, $needle, 0, false, $encoding, 'mb_strstr');
+        if (false === $pos) {
+            return false;
+        }
+        if ($part) {
+            return VmString::utf8CharSubstr($haystack, 0, $pos);
+        }
+        $charLen = VmString::utf8CharLength($haystack);
+
+        return VmString::utf8CharSubstr($haystack, $pos, $charLen - $pos);
+    }
+
     public static function substr(
         string $string,
         int $start,
diff --git a/ext/mbstring/mb_strstr.php b/ext/mbstring/mb_strstr.php
new file mode 100644
index 00000000000..1dc1c2ceb2f
--- /dev/null
+++ b/ext/mbstring/mb_strstr.php
@@ -0,0 +1,76 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler\ext\mbstring;
+
+use PHPCompiler\ext\standard\VmString;
+use PHPCompiler\Frame;
+use PHPCompiler\Func\Internal;
+use PHPCompiler\JIT\Context;
+use PHPCompiler\JIT\Variable as JITVariable;
+use PHPCompiler\VM\BuiltinExecute;
+use PHPCompiler\VM\Variable;
+use PHPLLVM\Value;
+
+/**
+ * mb_strstr() — multibyte strstr (php-src ext/mbstring/mbstring.c).
+ */
+final class mb_strstr extends Internal
+{
+    public function __construct()
+    {
+        parent::__construct('mb_strstr');
+    }
+
+    public function execute(Frame $frame): void
+    {
+        $argc = \count($frame->calledArgs);
+        if ($argc < 2 || $argc > 4) {
+            throw new \ArgumentCountError(sprintf(
+                'mb_strstr() expects at least 2 arguments, %d given',
+                $argc
+            ));
+        }
+        $haystack = VmString::coerceStringBuiltinArg(
+            $frame->calledArgs[0],
+            'mb_strstr',
+            0,
+            'haystack'
+        );
+        if (null === $frame->returnVar) {
+            return;
+        }
+        $needle = VmString::coerceStringBuiltinArg(
+            $frame->calledArgs[1],
+            'mb_strstr',
+            1,
+            'needle'
+        );
+        $part = $argc >= 3
+            ? VmMbstring::coercePartArg($frame->calledArgs[2], 'mb_strstr', 2)
+            : false;
+        $encoding = $argc >= 4
+            ? VmMbstring::coerceEncodingArg($frame->calledArgs[3], 'mb_strstr', 3)
+            : 'UTF-8';
+        $result = VmMbstring::strstr($haystack, $needle, $part, $encoding);
+        BuiltinExecute::writeReturn($frame, static function (Variable $ret) use ($result): void {
+            if (false === $result) {
+                $ret->bool(false);
+
+                return;
+            }
+            $ret->string($result);
+        });
+    }
+
+    public function call(Context $context, JITVariable ...$args): Value
+    {
+        $argc = \count($args);
+        if ($argc < 2 || $argc > 4) {
+            throw new \LogicException('mb_strstr() requires two to four arguments');
+        }
+
+        throw new \LogicException('mb_strstr() is not lowered for JIT/AOT in this compiler build');
+    }
+}
diff --git a/test/compliance/cases/stdlib/mb_strstr.phpt b/test/compliance/cases/stdlib/mb_strstr.phpt
new file mode 100644
index 00000000000..5fd8b13af28
--- /dev/null
+++ b/test/compliance/cases/stdlib/mb_strstr.phpt
@@ -0,0 +1,15 @@
+--TEST--
+stdlib mb_strstr() — multibyte strstr (#19941, ext/mbstring/mbstring.c)
+--FILE--
+<?php
+var_dump(mb_strstr('Hello World', 'World'));
+var_dump(mb_strstr('Hello World', 'World', true));
+var_dump(mb_strstr('Hello World', 'xyz'));
+var_dump(mb_strstr("caf\xC3\xA9 r\xC3\xA9sum\xC3\xA9", "\xC3\xA9"));
+var_dump(mb_strstr("caf\xC3\xA9 r\xC3\xA9sum\xC3\xA9", "\xC3\xA9", true));
+--EXPECT--
+string(5) "World"
+string(6) "Hello "
+bool(false)
+string(11) "é résumé"
+string(3) "caf"