[libcxx-commits] [libcxx] [libc++] Applied `[[nodiscard]]` to `__static_bounded_iter` (PR #198492)

[Hristo Hristov via libcxx-commits]

https://github.com/H-G-Hristov created https://github.com/llvm/llvm-project/pull/198492

Towards #172124

>From e62101e6753bbbb0c711871f1f0219883e96cf7f Mon Sep 17 00:00:00 2001
From: Hristo Hristov <hghristov.rmm at gmail.com>
Date: Tue, 19 May 2026 13:52:53 +0300
Subject: [PATCH] [libc++] Applied `[[nodiscard]]` to `__static_bounded_iter`

Towards #172124
---
 .../include/__iterator/static_bounded_iter.h  | 15 +++---
 ...nodiscard.__static_bounded_iter.verify.cpp | 47 +++++++++++++++++++
 2 files changed, 55 insertions(+), 7 deletions(-)
 create mode 100644 libcxx/test/libcxx/containers/sequences/array/nodiscard.__static_bounded_iter.verify.cpp

diff --git a/libcxx/include/__iterator/static_bounded_iter.h b/libcxx/include/__iterator/static_bounded_iter.h
index d8fc7d185e7bc..9663820109670 100644
--- a/libcxx/include/__iterator/static_bounded_iter.h
+++ b/libcxx/include/__iterator/static_bounded_iter.h
@@ -128,7 +128,7 @@ struct __static_bounded_iter {
 
 public:
   // Dereference and indexing operations.
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference operator*() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference operator*() const _NOEXCEPT {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         __current() != __end(), "__static_bounded_iter::operator*: Attempt to dereference an iterator at the end");
     return *__current();
@@ -140,7 +140,8 @@ struct __static_bounded_iter {
     return std::__to_address(__current());
   }
 
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference operator[](difference_type __n) const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference
+  operator[](difference_type __n) const _NOEXCEPT {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         __n >= __begin() - __current(),
         "__static_bounded_iter::operator[]: Attempt to index an iterator past the start");
@@ -186,13 +187,13 @@ struct __static_bounded_iter {
     __current() += __n;
     return *this;
   }
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend __static_bounded_iter
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend __static_bounded_iter
   operator+(__static_bounded_iter const& __self, difference_type __n) _NOEXCEPT {
     __static_bounded_iter __tmp(__self);
     __tmp += __n;
     return __tmp;
   }
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend __static_bounded_iter
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend __static_bounded_iter
   operator+(difference_type __n, __static_bounded_iter const& __self) _NOEXCEPT {
     __static_bounded_iter __tmp(__self);
     __tmp += __n;
@@ -208,13 +209,13 @@ struct __static_bounded_iter {
     __current() -= __n;
     return *this;
   }
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend __static_bounded_iter
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend __static_bounded_iter
   operator-(__static_bounded_iter const& __self, difference_type __n) _NOEXCEPT {
     __static_bounded_iter __tmp(__self);
     __tmp -= __n;
     return __tmp;
   }
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend difference_type
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 friend difference_type
   operator-(__static_bounded_iter const& __x, __static_bounded_iter const& __y) _NOEXCEPT {
     return __x.__current() - __y.__current();
   }
@@ -306,7 +307,7 @@ struct pointer_traits<__static_bounded_iter<_Iterator, _Size> > {
   using element_type    = typename pointer_traits<_Iterator>::element_type;
   using difference_type = typename pointer_traits<_Iterator>::difference_type;
 
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static element_type* to_address(pointer __it) _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static element_type* to_address(pointer __it) _NOEXCEPT {
     return std::__to_address(__it.__current());
   }
 };
diff --git a/libcxx/test/libcxx/containers/sequences/array/nodiscard.__static_bounded_iter.verify.cpp b/libcxx/test/libcxx/containers/sequences/array/nodiscard.__static_bounded_iter.verify.cpp
new file mode 100644
index 0000000000000..95e43cb7b9b86
--- /dev/null
+++ b/libcxx/test/libcxx/containers/sequences/array/nodiscard.__static_bounded_iter.verify.cpp
@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ABI_BOUNDED_ITERATORS_IN_STD_ARRAY
+
+// <array>
+
+// Check that functions are marked [[nodiscard]]
+
+#include <array>
+
+#include "test_macros.h"
+
+void test() { // __static_bounded_iter
+  typedef std::array<int, 94> Container;
+  ASSERT_SAME_TYPE(Container::iterator, std::__static_bounded_iter<int*, 94>);
+
+  Container::iterator it;
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  *it;
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  it[0];
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  it + 1;
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  1 + it;
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  it - 1;
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  it - it;
+
+  std::pointer_traits<Container::iterator> pt;
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  pt.to_address(it);
+}