From ee6f2351af8fea15b8640b3e280345e2a96ef737 Mon Sep 17 00:00:00 2001
From: Ilia Alshanetsky <ilia@ilia.ws>
Date: Mon, 24 Aug 2026 11:12:35 -0400
Subject: [PATCH] [intl] Fix empty-needle grapheme_strpos offsets

grapheme_strpos_utf16() returned raw UTF-16 code-unit positions for an
empty needle instead of grapheme counts, so multi-code-unit graphemes
made strpos()/strrpos() over-report the offset. Convert the boundary
position like the non-empty search path; sibling audit found the ASCII
fast paths and the strstr() UTF-16 position consumer are unaffected.

Signed-off-by: Ilia Alshanetsky <ilia@ilia.ws>
---
 NEWS                                          |  2 ++
 ext/intl/grapheme/grapheme_util.c             |  6 +++-
 .../grapheme_empty_offset_multibyte.phpt      | 36 +++++++++++++++++++
 3 files changed, 43 insertions(+), 1 deletion(-)
 create mode 100644 ext/intl/tests/grapheme_empty_offset_multibyte.phpt

diff --git a/NEWS b/NEWS
index a2c65685b4ce..16684e86ebb2 100644
--- a/NEWS
+++ b/NEWS
@@ -28,6 +28,8 @@ PHP                                                                        NEWS
   . Fixed Locale::parseLocale() reading past a trailing '-' or '_'.
     (iliaal, Xuyang Zhang)
   . Fixed grapheme_str_split() treating UBRK_DONE as a byte index. (iliaal)
+  . Fixed grapheme_strpos() and grapheme_strrpos() with an empty needle
+    returning UTF-16 offsets instead of grapheme offsets. (iliaal)
 
 - Opcache:
   . Fixed opcache.protect_memory race under ZTS. (realFlowControl)
diff --git a/ext/intl/grapheme/grapheme_util.c b/ext/intl/grapheme/grapheme_util.c
index 501b9dfb221d..f0c79785483f 100644
--- a/ext/intl/grapheme/grapheme_util.c
+++ b/ext/intl/grapheme/grapheme_util.c
@@ -131,7 +131,11 @@ int32_t grapheme_strpos_utf16(char *haystack, size_t haystack_len, char *needle,
 			ret_pos = -1;
 			goto finish;
 		}
-		ret_pos = last && offset >= 0 ? uhaystack_len : offset_pos;
+		if (last && offset >= 0) {
+			ret_pos = grapheme_count_graphemes(bi, uhaystack, uhaystack_len);
+		} else {
+			ret_pos = grapheme_count_graphemes(bi, uhaystack, offset_pos);
+		}
 		goto finish;
 	}
 
diff --git a/ext/intl/tests/grapheme_empty_offset_multibyte.phpt b/ext/intl/tests/grapheme_empty_offset_multibyte.phpt
new file mode 100644
index 000000000000..c2f997140eb3
--- /dev/null
+++ b/ext/intl/tests/grapheme_empty_offset_multibyte.phpt
@@ -0,0 +1,36 @@
+--TEST--
+grapheme_strpos() family with empty needle and offset on multi-code-unit graphemes
+--EXTENSIONS--
+intl
+--FILE--
+<?php
+
+ini_set("intl.error_level", E_WARNING);
+
+var_dump(grapheme_strpos("😀x", ""));
+var_dump(grapheme_strpos("😀x", "", 0));
+var_dump(grapheme_strpos("😀x", "", 1));
+var_dump(grapheme_stripos("😀x", "", 1));
+var_dump(grapheme_strpos("😀x", "", -1));
+var_dump(grapheme_strrpos("😀x", ""));
+var_dump(grapheme_strrpos("😀x", "", 1));
+var_dump(grapheme_strripos("😀x", "", 1));
+var_dump(grapheme_strrpos("😀x", "", -1));
+try {
+    var_dump(grapheme_strpos("😀x", "", 5));
+} catch (ValueError $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+int(0)
+int(0)
+int(1)
+int(1)
+int(1)
+int(2)
+int(2)
+int(2)
+int(1)
+grapheme_strpos(): Argument #3 ($offset) must be contained in argument #1 ($haystack)