[libcxx-commits] [libcxx] [libc++] Fix random_shuffle in __cxx03/__algorithm/shuffle.h (PR #186434)

[Zibi Sarbinowski via libcxx-commits]

https://github.com/zibi2 created https://github.com/llvm/llvm-project/pull/186434

Frozen cxx03 header should use reference for the 3rd parameter of random_shuffle() template function.
The c++03 only test was added as requested in previous attempt in PR https://github.com/llvm/llvm-project/pull/155915.

>From 6ff1f6d772cd335558ffe81bcfa60967950b5feb Mon Sep 17 00:00:00 2001
From: Zibi Sarbinowski <zibi at ca.ibm.com>
Date: Thu, 28 Aug 2025 20:14:34 +0000
Subject: [PATCH 1/2] Fix random_shuffle in __cxx03/__algorithm/shuffle.h

---
 libcxx/include/__cxx03/__algorithm/shuffle.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libcxx/include/__cxx03/__algorithm/shuffle.h b/libcxx/include/__cxx03/__algorithm/shuffle.h
index fee7028ae22ac..24cd71c71378b 100644
--- a/libcxx/include/__cxx03/__algorithm/shuffle.h
+++ b/libcxx/include/__cxx03/__algorithm/shuffle.h
@@ -109,7 +109,7 @@ _LIBCPP_HIDE_FROM_ABI void random_shuffle(_RandomAccessIterator __first, _Random
 
 template <class _RandomAccessIterator, class _RandomNumberGenerator>
 _LIBCPP_HIDE_FROM_ABI void
-random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last, _RandomNumberGenerator&& __rand) {
+random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last, _RandomNumberGenerator& __rand) {
   typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
   difference_type __d = __last - __first;
   if (__d > 1) {

>From d81c3da99754d2c9e5d75810bd166c280a11c0af Mon Sep 17 00:00:00 2001
From: Zibi Sarbinowski <zibi at ca.ibm.com>
Date: Fri, 13 Mar 2026 16:15:41 +0000
Subject: [PATCH 2/2] Add c++03 only lit test

---
 .../random.shuffle.funcptr.compile.pass.cpp   | 44 +++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 libcxx/test/std/algorithms/alg.sorting/alg.random.shuffle/random.shuffle.funcptr.compile.pass.cpp

diff --git a/libcxx/test/std/algorithms/alg.sorting/alg.random.shuffle/random.shuffle.funcptr.compile.pass.cpp b/libcxx/test/std/algorithms/alg.sorting/alg.random.shuffle/random.shuffle.funcptr.compile.pass.cpp
new file mode 100644
index 0000000000000..7a0b08f77fe06
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.sorting/alg.random.shuffle/random.shuffle.funcptr.compile.pass.cpp
@@ -0,0 +1,44 @@
+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// UNSUPPORTED: c++11, c++14, c++17, c++20, c++26, c++2b, c++2c
+//
+// This test verifies that the std::random_shuffle overload taking a
+// random-number generator function (legacy) is available and callable
+// in dialects where random_shuffle is still provided ( == C++03).
+//
+// Compile-only, so it can run under c++03 as well.
+//
+//===----------------------------------------------------------------------===//
+
+#include <algorithm>
+#include <vector>
+#include <iterator>
+
+typedef std::vector<int>::iterator Iter;
+typedef std::iterator_traits<Iter>::difference_type Diff;
+typedef Diff (*RandomNumberGenerator)(Diff);
+
+// Wrapper that calls the legacy random_shuffle overload with RNG by reference.
+void f(Iter a1, Iter a2, RandomNumberGenerator& a3) {
+    std::random_shuffle<Iter, RandomNumberGenerator>(a1, a2, a3);
+}
+
+// A minimal RNG with the required signature. Behavior doesn't matter for compile test.
+static Diff rng(Diff n) {
+    return (n <= 1) ? 0 : (n - 1); // returns in [0, n)
+}
+
+int main() {
+    // Use a C array to avoid C++11 initializer_list; this is valid in C++03.
+    int data[] = {0, 1, 2, 3, 4};
+    std::vector<int> v(data, data + sizeof(data)/sizeof(data[0]));
+
+    RandomNumberGenerator g = &rng;
+    f(v.begin(), v.end(), g);
+    return 0;
+}