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[libc++][format] Applied [[nodiscard]] to more classes #170808

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Merged
frederick-vs-ja merged 3 commits into from
Dec 12, 2025
Merged

[libc++][format] Applied [[nodiscard]] to more classes #170808

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7d3001b
[libc++][charconv]
H-G-Hristov Dec 5, 2025
d5dfc42
Revert
H-G-Hristov Dec 5, 2025
511d6b3
[libc++][format] Applied `[[nodiscard]]` to more classes
H-G-Hristov Dec 5, 2025
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2 changes: 1 addition & 1 deletion libcxx/include/__format/format_args.h
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,7 @@ class basic_format_args {
}
}

_LIBCPP_HIDE_FROM_ABI basic_format_arg<_Context> get(size_t __id) const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI basic_format_arg<_Context> get(size_t __id) const noexcept {
if (__id >= __size_)
return basic_format_arg<_Context>{};

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6 changes: 3 additions & 3 deletions libcxx/include/__format/format_context.h
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Expand Up @@ -80,17 +80,17 @@ class _LIBCPP_PREFERRED_NAME(format_context)
template <class _Tp>
using formatter_type = formatter<_Tp, _CharT>;

_LIBCPP_HIDE_FROM_ABI basic_format_arg<basic_format_context> arg(size_t __id) const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI basic_format_arg<basic_format_context> arg(size_t __id) const noexcept {
return __args_.get(__id);
}
# if _LIBCPP_HAS_LOCALIZATION
_LIBCPP_HIDE_FROM_ABI std::locale locale() {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI std::locale locale() {
if (!__loc_)
__loc_ = std::locale{};
return *__loc_;
}
# endif
_LIBCPP_HIDE_FROM_ABI iterator out() { return std::move(__out_it_); }
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI iterator out() { return std::move(__out_it_); }
_LIBCPP_HIDE_FROM_ABI void advance_to(iterator __it) { __out_it_ = std::move(__it); }

private:
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4 changes: 2 additions & 2 deletions libcxx/include/__format/format_parse_context.h
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Expand Up @@ -41,8 +41,8 @@ class basic_format_parse_context {
basic_format_parse_context(const basic_format_parse_context&) = delete;
basic_format_parse_context& operator=(const basic_format_parse_context&) = delete;

_LIBCPP_HIDE_FROM_ABI constexpr const_iterator begin() const noexcept { return __begin_; }
_LIBCPP_HIDE_FROM_ABI constexpr const_iterator end() const noexcept { return __end_; }
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const_iterator begin() const noexcept { return __begin_; }
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const_iterator end() const noexcept { return __end_; }
_LIBCPP_HIDE_FROM_ABI constexpr void advance_to(const_iterator __it) { __begin_ = __it; }

_LIBCPP_HIDE_FROM_ABI constexpr size_t next_arg_id() {
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23 changes: 23 additions & 0 deletions libcxx/test/libcxx/diagnostics/format.nodiscard.verify.cpp
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Expand Up @@ -14,7 +14,9 @@
// UNSUPPORTED: c++03, c++11, c++14, c++17

#include <format>
#include <string>

#include "test_format_context.h"
#include "test_macros.h"

#ifndef TEST_HAS_NO_LOCALIZATION
Expand Down Expand Up @@ -46,4 +48,25 @@ void test() {
# endif // TEST_HAS_NO_WIDE_CHARACTERS
#endif // TEST_HAS_NO_LOCALIZATION
// clang-format on

std::basic_format_args args{std::make_format_args()};

args.get(0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

using OutItT = std::back_insert_iterator<std::string>;
std::string str;
OutItT outIt{str};
using FormatCtxT = std::basic_format_context<OutItT, char>;
FormatCtxT fCtx = test_format_context_create<OutItT, char>(outIt, std::make_format_args<FormatCtxT>());

fCtx.arg(0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
#if !defined(TEST_HAS_NO_LOCALIZATION)
fCtx.locale(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
#endif
fCtx.out(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

std::basic_format_parse_context<char> fpCtx{""};

fpCtx.begin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fpCtx.end(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
}
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