[libc++][filesystem] Applied `[[nodiscard]]` #171085

H-G-Hristov · 2025-12-08T07:41:59Z

[[nodiscard]] should be applied to functions where discarding the return value is most likely a correctness issue.

https://libcxx.llvm.org/CodingGuidelines.html

github-actions · 2025-12-08T07:43:42Z

✅ With the latest revision this PR passed the C/C++ code formatter.

H-G-Hristov · 2025-12-10T11:35:30Z

https://ci.chromium.org/p/fuchsia/g/llvm/console

`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue. - https://libcxx.llvm.org/CodingGuidelines.html

llvmbot · 2025-12-10T17:48:49Z

@llvm/pr-subscribers-libcxx

Author: Hristo Hristov (H-G-Hristov)

Changes

[[nodiscard]] should be applied to functions where discarding the return value is most likely a correctness issue.

https://libcxx.llvm.org/CodingGuidelines.html

Patch is 76.44 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/171085.diff

15 Files Affected:

(modified) libcxx/include/__filesystem/copy_options.h (+7-7)
(modified) libcxx/include/__filesystem/directory_entry.h (+37-29)
(modified) libcxx/include/__filesystem/directory_iterator.h (+7-3)
(modified) libcxx/include/__filesystem/directory_options.h (+7-4)
(modified) libcxx/include/__filesystem/file_status.h (+2-2)
(modified) libcxx/include/__filesystem/filesystem_error.h (+6-5)
(modified) libcxx/include/__filesystem/operations.h (+97-62)
(modified) libcxx/include/__filesystem/path.h (+61-55)
(modified) libcxx/include/__filesystem/path_iterator.h (+1-1)
(modified) libcxx/include/__filesystem/perm_options.h (+4-4)
(modified) libcxx/include/__filesystem/perms.h (+4-4)
(modified) libcxx/include/__filesystem/recursive_directory_iterator.h (+7-6)
(modified) libcxx/include/__filesystem/u8path.h (+3-3)
(modified) libcxx/test/libcxx/diagnostics/filesystem.nodiscard.verify.cpp (+440-4)
(modified) libcxx/test/std/input.output/filesystems/fs.op.funcs/fs.op.status/status.pass.cpp (+1-1)

diff --git a/libcxx/include/__filesystem/copy_options.h b/libcxx/include/__filesystem/copy_options.h
index 097eebe61137d..cba719dbed1f6 100644
--- a/libcxx/include/__filesystem/copy_options.h
+++ b/libcxx/include/__filesystem/copy_options.h
@@ -34,31 +34,31 @@ enum class copy_options : unsigned short {
   __in_recursive_copy = 512,
 };
 
-_LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator&(copy_options __lhs, copy_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator&(copy_options __lhs, copy_options __rhs) {
   return static_cast<copy_options>(static_cast<unsigned short>(__lhs) & static_cast<unsigned short>(__rhs));
 }
 
-_LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator|(copy_options __lhs, copy_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator|(copy_options __lhs, copy_options __rhs) {
   return static_cast<copy_options>(static_cast<unsigned short>(__lhs) | static_cast<unsigned short>(__rhs));
 }
 
-_LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator^(copy_options __lhs, copy_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator^(copy_options __lhs, copy_options __rhs) {
   return static_cast<copy_options>(static_cast<unsigned short>(__lhs) ^ static_cast<unsigned short>(__rhs));
 }
 
-_LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator~(copy_options __lhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator~(copy_options __lhs) {
   return static_cast<copy_options>(~static_cast<unsigned short>(__lhs));
 }
 
-_LIBCPP_HIDE_FROM_ABI inline copy_options& operator&=(copy_options& __lhs, copy_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline copy_options& operator&=(copy_options& __lhs, copy_options __rhs) {
   return __lhs = __lhs & __rhs;
 }
 
-_LIBCPP_HIDE_FROM_ABI inline copy_options& operator|=(copy_options& __lhs, copy_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline copy_options& operator|=(copy_options& __lhs, copy_options __rhs) {
   return __lhs = __lhs | __rhs;
 }
 
-_LIBCPP_HIDE_FROM_ABI inline copy_options& operator^=(copy_options& __lhs, copy_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline copy_options& operator^=(copy_options& __lhs, copy_options __rhs) {
   return __lhs = __lhs ^ __rhs;
 }
 
diff --git a/libcxx/include/__filesystem/directory_entry.h b/libcxx/include/__filesystem/directory_entry.h
index 3513a4975ad8f..fab400b439429 100644
--- a/libcxx/include/__filesystem/directory_entry.h
+++ b/libcxx/include/__filesystem/directory_entry.h
@@ -87,80 +87,88 @@ class directory_entry {
 
   _LIBCPP_HIDE_FROM_ABI void refresh(error_code& __ec) noexcept { __refresh(&__ec); }
 
-  _LIBCPP_HIDE_FROM_ABI _Path const& path() const noexcept { return __p_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI _Path const& path() const noexcept { return __p_; }
 
   _LIBCPP_HIDE_FROM_ABI operator const _Path&() const noexcept { return __p_; }
 
-  _LIBCPP_HIDE_FROM_ABI bool exists() const { return filesystem::exists(file_status{__get_ft()}); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool exists() const { return filesystem::exists(file_status{__get_ft()}); }
 
-  _LIBCPP_HIDE_FROM_ABI bool exists(error_code& __ec) const noexcept {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool exists(error_code& __ec) const noexcept {
     return filesystem::exists(file_status{__get_ft(&__ec)});
   }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_block_file() const { return __get_ft() == file_type::block; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_block_file() const { return __get_ft() == file_type::block; }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_block_file(error_code& __ec) const noexcept {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_block_file(error_code& __ec) const noexcept {
     return __get_ft(&__ec) == file_type::block;
   }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_character_file() const { return __get_ft() == file_type::character; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_character_file() const { return __get_ft() == file_type::character; }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_character_file(error_code& __ec) const noexcept {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_character_file(error_code& __ec) const noexcept {
     return __get_ft(&__ec) == file_type::character;
   }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_directory() const { return __get_ft() == file_type::directory; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_directory() const { return __get_ft() == file_type::directory; }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_directory(error_code& __ec) const noexcept {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_directory(error_code& __ec) const noexcept {
     return __get_ft(&__ec) == file_type::directory;
   }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_fifo() const { return __get_ft() == file_type::fifo; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_fifo() const { return __get_ft() == file_type::fifo; }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_fifo(error_code& __ec) const noexcept { return __get_ft(&__ec) == file_type::fifo; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_fifo(error_code& __ec) const noexcept {
+    return __get_ft(&__ec) == file_type::fifo;
+  }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_other() const { return filesystem::is_other(file_status{__get_ft()}); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_other() const { return filesystem::is_other(file_status{__get_ft()}); }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_other(error_code& __ec) const noexcept {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_other(error_code& __ec) const noexcept {
     return filesystem::is_other(file_status{__get_ft(&__ec)});
   }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_regular_file() const { return __get_ft() == file_type::regular; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_regular_file() const { return __get_ft() == file_type::regular; }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_regular_file(error_code& __ec) const noexcept {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_regular_file(error_code& __ec) const noexcept {
     return __get_ft(&__ec) == file_type::regular;
   }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_socket() const { return __get_ft() == file_type::socket; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_socket() const { return __get_ft() == file_type::socket; }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_socket(error_code& __ec) const noexcept { return __get_ft(&__ec) == file_type::socket; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_socket(error_code& __ec) const noexcept {
+    return __get_ft(&__ec) == file_type::socket;
+  }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_symlink() const { return __get_sym_ft() == file_type::symlink; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_symlink() const { return __get_sym_ft() == file_type::symlink; }
 
-  _LIBCPP_HIDE_FROM_ABI bool is_symlink(error_code& __ec) const noexcept {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_symlink(error_code& __ec) const noexcept {
     return __get_sym_ft(&__ec) == file_type::symlink;
   }
-  _LIBCPP_HIDE_FROM_ABI uintmax_t file_size() const { return __get_size(); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI uintmax_t file_size() const { return __get_size(); }
 
-  _LIBCPP_HIDE_FROM_ABI uintmax_t file_size(error_code& __ec) const noexcept { return __get_size(&__ec); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI uintmax_t file_size(error_code& __ec) const noexcept { return __get_size(&__ec); }
 
-  _LIBCPP_HIDE_FROM_ABI uintmax_t hard_link_count() const { return __get_nlink(); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI uintmax_t hard_link_count() const { return __get_nlink(); }
 
-  _LIBCPP_HIDE_FROM_ABI uintmax_t hard_link_count(error_code& __ec) const noexcept { return __get_nlink(&__ec); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI uintmax_t hard_link_count(error_code& __ec) const noexcept {
+    return __get_nlink(&__ec);
+  }
 
-  _LIBCPP_HIDE_FROM_ABI file_time_type last_write_time() const { return __get_write_time(); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI file_time_type last_write_time() const { return __get_write_time(); }
 
-  _LIBCPP_HIDE_FROM_ABI file_time_type last_write_time(error_code& __ec) const noexcept {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI file_time_type last_write_time(error_code& __ec) const noexcept {
     return __get_write_time(&__ec);
   }
 
-  _LIBCPP_HIDE_FROM_ABI file_status status() const { return __get_status(); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI file_status status() const { return __get_status(); }
 
-  _LIBCPP_HIDE_FROM_ABI file_status status(error_code& __ec) const noexcept { return __get_status(&__ec); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI file_status status(error_code& __ec) const noexcept {
+    return __get_status(&__ec);
+  }
 
-  _LIBCPP_HIDE_FROM_ABI file_status symlink_status() const { return __get_symlink_status(); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI file_status symlink_status() const { return __get_symlink_status(); }
 
-  _LIBCPP_HIDE_FROM_ABI file_status symlink_status(error_code& __ec) const noexcept {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI file_status symlink_status(error_code& __ec) const noexcept {
     return __get_symlink_status(&__ec);
   }
 
diff --git a/libcxx/include/__filesystem/directory_iterator.h b/libcxx/include/__filesystem/directory_iterator.h
index 5e9fea636de0b..b62129807b567 100644
--- a/libcxx/include/__filesystem/directory_iterator.h
+++ b/libcxx/include/__filesystem/directory_iterator.h
@@ -71,7 +71,7 @@ class directory_iterator {
 
   _LIBCPP_HIDE_FROM_ABI ~directory_iterator() = default;
 
-  _LIBCPP_HIDE_FROM_ABI const directory_entry& operator*() const {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI const directory_entry& operator*() const {
     // Note: this check duplicates a check in `__dereference()`.
     _LIBCPP_ASSERT_NON_NULL(__imp_, "The end iterator cannot be dereferenced");
     return __dereference();
@@ -121,9 +121,13 @@ operator!=(const directory_iterator& __lhs, const directory_iterator& __rhs) noe
 }
 
 // enable directory_iterator range-based for statements
-inline _LIBCPP_HIDE_FROM_ABI directory_iterator begin(directory_iterator __iter) noexcept { return __iter; }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI directory_iterator begin(directory_iterator __iter) noexcept {
+  return __iter;
+}
 
-inline _LIBCPP_HIDE_FROM_ABI directory_iterator end(directory_iterator) noexcept { return directory_iterator(); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI directory_iterator end(directory_iterator) noexcept {
+  return directory_iterator();
+}
 
 _LIBCPP_END_NAMESPACE_FILESYSTEM
 
diff --git a/libcxx/include/__filesystem/directory_options.h b/libcxx/include/__filesystem/directory_options.h
index d0cd3ebfdaa7e..11c7d204ea824 100644
--- a/libcxx/include/__filesystem/directory_options.h
+++ b/libcxx/include/__filesystem/directory_options.h
@@ -22,19 +22,22 @@ _LIBCPP_BEGIN_NAMESPACE_FILESYSTEM
 
 enum class directory_options : unsigned char { none = 0, follow_directory_symlink = 1, skip_permission_denied = 2 };
 
-_LIBCPP_HIDE_FROM_ABI inline constexpr directory_options operator&(directory_options __lhs, directory_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr directory_options
+operator&(directory_options __lhs, directory_options __rhs) {
   return static_cast<directory_options>(static_cast<unsigned char>(__lhs) & static_cast<unsigned char>(__rhs));
 }
 
-_LIBCPP_HIDE_FROM_ABI inline constexpr directory_options operator|(directory_options __lhs, directory_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr directory_options
+operator|(directory_options __lhs, directory_options __rhs) {
   return static_cast<directory_options>(static_cast<unsigned char>(__lhs) | static_cast<unsigned char>(__rhs));
 }
 
-_LIBCPP_HIDE_FROM_ABI inline constexpr directory_options operator^(directory_options __lhs, directory_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr directory_options
+operator^(directory_options __lhs, directory_options __rhs) {
   return static_cast<directory_options>(static_cast<unsigned char>(__lhs) ^ static_cast<unsigned char>(__rhs));
 }
 
-_LIBCPP_HIDE_FROM_ABI inline constexpr directory_options operator~(directory_options __lhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr directory_options operator~(directory_options __lhs) {
   return static_cast<directory_options>(~static_cast<unsigned char>(__lhs));
 }
 
diff --git a/libcxx/include/__filesystem/file_status.h b/libcxx/include/__filesystem/file_status.h
index eecaf3c492f03..746cd0f9a680c 100644
--- a/libcxx/include/__filesystem/file_status.h
+++ b/libcxx/include/__filesystem/file_status.h
@@ -38,9 +38,9 @@ class file_status {
   _LIBCPP_HIDE_FROM_ABI file_status& operator=(file_status&&) noexcept      = default;
 
   // observers
-  _LIBCPP_HIDE_FROM_ABI file_type type() const noexcept { return __ft_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI file_type type() const noexcept { return __ft_; }
 
-  _LIBCPP_HIDE_FROM_ABI perms permissions() const noexcept { return __prms_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI perms permissions() const noexcept { return __prms_; }
 
   // modifiers
   _LIBCPP_HIDE_FROM_ABI void type(file_type __ft) noexcept { __ft_ = __ft; }
diff --git a/libcxx/include/__filesystem/filesystem_error.h b/libcxx/include/__filesystem/filesystem_error.h
index 0df170f3d3a9f..6f1daf866a504 100644
--- a/libcxx/include/__filesystem/filesystem_error.h
+++ b/libcxx/include/__filesystem/filesystem_error.h
@@ -44,15 +44,16 @@ class _LIBCPP_EXPORTED_FROM_ABI filesystem_error : public system_error {
     __create_what(2);
   }
 
-  _LIBCPP_HIDE_FROM_ABI const path& path1() const noexcept { return __storage_->__p1_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI const path& path1() const noexcept { return __storage_->__p1_; }
 
-  _LIBCPP_HIDE_FROM_ABI const path& path2() const noexcept { return __storage_->__p2_; }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI const path& path2() const noexcept { return __storage_->__p2_; }
 
-  _LIBCPP_HIDE_FROM_ABI filesystem_error(const filesystem_error&) = default;
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI filesystem_error(const filesystem_error&) = default;
   ~filesystem_error() override; // key function
 
-  _LIBCPP_HIDE_FROM_ABI_VIRTUAL
-  const char* what() const noexcept override { return __storage_->__what_.c_str(); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI_VIRTUAL const char* what() const noexcept override {
+    return __storage_->__what_.c_str();
+  }
 
   void __create_what(int __num_paths);
 
diff --git a/libcxx/include/__filesystem/operations.h b/libcxx/include/__filesystem/operations.h
index 0fd55c19414c4..f536a1a9d4466 100644
--- a/libcxx/include/__filesystem/operations.h
+++ b/libcxx/include/__filesystem/operations.h
@@ -68,10 +68,14 @@ _LIBCPP_EXPORTED_FROM_ABI bool __fs_is_empty(const path& __p, error_code* __ec =
 _LIBCPP_EXPORTED_FROM_ABI void __permissions(const path&, perms, perm_options, error_code* = nullptr);
 _LIBCPP_EXPORTED_FROM_ABI space_info __space(const path&, error_code* __ec = nullptr);
 
-inline _LIBCPP_HIDE_FROM_ABI path absolute(const path& __p) { return __absolute(__p); }
-inline _LIBCPP_HIDE_FROM_ABI path absolute(const path& __p, error_code& __ec) { return __absolute(__p, &__ec); }
-inline _LIBCPP_HIDE_FROM_ABI path canonical(const path& __p) { return __canonical(__p); }
-inline _LIBCPP_HIDE_FROM_ABI path canonical(const path& __p, error_code& __ec) { return __canonical(__p, &__ec); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI path absolute(const path& __p) { return __absolute(__p); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI path absolute(const path& __p, error_code& __ec) {
+  return __absolute(__p, &__ec);
+}
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI path canonical(const path& __p) { return __canonical(__p); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI path canonical(const path& __p, error_code& __ec) {
+  return __canonical(__p, &__ec);
+}
 inline _LIBCPP_HIDE_FROM_ABI bool copy_file(const path& __from, const path& __to) {
   return __copy_file(__from, __to, copy_options::none);
 }
@@ -135,85 +139,112 @@ inline _LIBCPP_HIDE_FROM_ABI void create_symlink(const path& __target, const pat
 inline _LIBCPP_HIDE_FROM_ABI void create_symlink(const path& __target, const path& __link, error_code& __ec) noexcept {
   return __create_symlink(__target, __link, &__ec);
 }
-inline _LIBCPP_HIDE_FROM_ABI path current_path() { return __current_path(); }
-inline _LIBCPP_HIDE_FROM_ABI path current_path(error_code& __ec) { return __current_path(&__ec); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI path current_path() { return __current_path(); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI path current_path(error_code& __ec) { return __current_path(&__ec); }
 inline _LIBCPP_HIDE_FROM_ABI void current_path(const path& __p) { __current_path(__p); }
 inline _LIBCPP_HIDE_FROM_ABI void current_path(const path& __p, error_code& __ec) noexcept {
   __current_path(__p, &__ec);
 }
-inline _LIBCPP_HIDE_FROM_ABI bool equivalent(const path& __p1, const path& __p2) { return __equivalent(__p1, __p2); }
-inline _LIBCPP_HIDE_FROM_ABI bool equivalent(const path& __p1, const path& __p2, error_code& __ec) noexcept {
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool equivalent(const path& __p1, const path& __p2) {
+  return __equivalent(__p1, __p2);
+}
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool
+equivalent(const path& __p1, const path& __p2, error_code& __ec) noexcept {
   return __equivalent(__p1, __p2, &__ec);
 }
-inline _LIBCPP_HIDE_FROM_ABI bool status_known(file_status __s) noexcept { return __s.type() != file_type::none; }
-inline _LIBCPP_HIDE_FROM_ABI bool exists(file_status __s) noexcept {
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool status_known(file_status __s) noexcept {
+  return __s.type() != file_type::none;
+}
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool exists(file_status __s) noexcept {
   return status_known(__s) && __s.type() != file_type::not_found;
 }
-inline _LIBCPP_HIDE_FROM_ABI bool exists(const path& __p) { return exists(__status(__p)); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool exists(const path& __p) { return exists(__status(__p)); }
 
-inline _LIBCPP_HIDE_FROM_ABI bool exists(const path& __p, error_code& __ec) noexcept {
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool exists(const path& __p, error_code& __ec) noexcept {
   auto __s = __status(__p, &__ec);
   if (status_known(__s))
     __ec.clear();
   return exists(__s);
 }
 
-inline _LIBCPP_HIDE_FROM_ABI uintmax_t file_size(const path& __p) { return __file_size(__p); }
-inline _LIBCPP_HIDE_FROM_ABI uintmax_t file_size(const path& __p, error_code& __ec) noexcept {
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI uintmax_t file_size(const path& __p) { return __file_size(__p); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI uintmax_t file_size(const path& __p, error_code& __ec) noexcept {
   return __file_size(__p, &__ec);
 }
-inline _LIBCPP_HIDE_FROM_ABI uintmax_t hard_link_count(const path& __p) { return __hard_link_count(__p); }
-inline _LIBCPP_HIDE_FROM_ABI uintmax_t hard_link_count(const path& __p, error_code& __ec) noexcept {
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI uintmax_t hard_link_count(const path& __p) { return __hard_link_count(__p); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI uintmax_t hard_link_count(const path& __p, error_code& __ec) noexcept {
   return __hard_link_count(__p, &__ec);
 }
-inline _LIBCPP_HIDE_FROM_ABI bool is_block_file(file_status __s) noexcept { return __s.type() == file_type::block; }
-inline _LIBCPP_HIDE_FROM_ABI bool is_block_file(const path& __p) { return is_block_file(__status(__p)); }
-inline _LIBCPP_HIDE_FROM_ABI bool is_block_file(const path& __p, error_code& __ec) noexcept {
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool is_block_file(file_status __s) noexcept {
+  return __s.type() == file_type::block;
+}
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool is_block_file(const path& __p) { return is_block_file(__status(__p)); }
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool is_block_file(const path& __p, error_code& __ec) noexcept {
   return is_block_file(__status(__p, &__ec));
 }
-inline _LIBCPP_HIDE_FROM_ABI bool is_character_file(file_status __s) noexcept {
+[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool is_character_file(file_status __s) noexcept {
   return __s.type() == file_type::character;
 }
-inline _LIBCPP_HIDE_FROM_ABI bool is_character_file(const path& __p) { retur...
[truncated]

frederick-vs-ja · 2025-12-12T03:49:39Z

libcxx/include/__filesystem/u8path.h

@@ -49,7 +49,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_WITH_CHAR8_T path u8path(_InputIt __f,

 #  if defined(_LIBCPP_WIN32API) && _LIBCPP_HAS_LOCALIZATION
 template <class _InputIt, __enable_if_t<__is_pathable<_InputIt>::value, int> = 0>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_WITH_CHAR8_T path u8path(_InputIt __f, _NullSentinel) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_WITH_CHAR8_T path u8path(_InputIt __f, _NullSentinel) {


I strongly believe that this overload is non-conforming and should be removed (or reformed, but I strongly think that removal will be better). I think it would be better to avoid touching it, given it's not being tested. (No change strictly requested.)

frederick-vs-ja · 2025-12-12T03:53:31Z

libcxx/test/libcxx/diagnostics/filesystem.nodiscard.verify.cpp

+  {
+    const std::string str;
+
+#if !defined(TEST_HAS_NO_LOCALIZATION)


No change requested as fixed should be in a future PR. This is quite weird. If localization is unavailable, we should use non-transcoded strings as-is, so IMO these uses of u8path should be always available.

libcxx/include/__filesystem/copy_options.h

philnik777 · 2025-12-12T08:38:27Z

libcxx/include/__filesystem/copy_options.h

+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator&(copy_options __lhs, copy_options __rhs) {
  return static_cast<copy_options>(static_cast<unsigned short>(__lhs) & static_cast<unsigned short>(__rhs));
 }

-_LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator|(copy_options __lhs, copy_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator|(copy_options __lhs, copy_options __rhs) {
  return static_cast<copy_options>(static_cast<unsigned short>(__lhs) | static_cast<unsigned short>(__rhs));
 }

-_LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator^(copy_options __lhs, copy_options __rhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator^(copy_options __lhs, copy_options __rhs) {
  return static_cast<copy_options>(static_cast<unsigned short>(__lhs) ^ static_cast<unsigned short>(__rhs));
 }

-_LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator~(copy_options __lhs) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline constexpr copy_options operator~(copy_options __lhs) {
  return static_cast<copy_options>(~static_cast<unsigned short>(__lhs));
 }


Why were these added? Clang should warn without any annotations.

But currently Clang doesn't. Is there already a PR for this?

Currently Clang doesn't do that:
https://godbolt.org/z/36TGdT9a9

`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue. - https://libcxx.llvm.org/CodingGuidelines.html

H-G-Hristov force-pushed the hgh/libcxx/nodiscard-to-filesystem branch 10 times, most recently from 17aa146 to ca708a0 Compare December 10, 2025 10:18

[libc++][filesystem] Applied [[nodiscard]]

ad6f10f

`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue. - https://libcxx.llvm.org/CodingGuidelines.html

H-G-Hristov force-pushed the hgh/libcxx/nodiscard-to-filesystem branch from ca708a0 to ad6f10f Compare December 10, 2025 11:44

H-G-Hristov marked this pull request as ready for review December 10, 2025 17:48

H-G-Hristov requested a review from a team as a code owner December 10, 2025 17:48

llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Dec 10, 2025

frederick-vs-ja approved these changes Dec 12, 2025

View reviewed changes

Zingam merged commit c05a3ac into llvm:main Dec 12, 2025
83 checks passed

philnik777 reviewed Dec 12, 2025

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H-G-Hristov mentioned this pull request Dec 13, 2025

[libc++] Apply [[nodiscard]] to the Standard Library #172124

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