[libcxx-commits] [libcxx] [libc++] Applied `[[nodiscard]]` to `<exception>`, `<stdexcept>` and `<system_error>` (PR #170837)
via libcxx-commits
libcxx-commits at lists.llvm.org
Sat Dec 6 01:57:10 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Hristo Hristov (H-G-Hristov)
<details>
<summary>Changes</summary>
[[nodiscard]] should be applied to functions where discarding the return value is most likely a correctness issue.
- https://libcxx.llvm.org/CodingGuidelines.html
---
Full diff: https://github.com/llvm/llvm-project/pull/170837.diff
10 Files Affected:
- (modified) libcxx/include/__exception/exception.h (+5-3)
- (modified) libcxx/include/__exception/nested_exception.h (+1-1)
- (modified) libcxx/include/__exception/operations.h (+5-5)
- (modified) libcxx/include/__system_error/error_category.h (+7-7)
- (modified) libcxx/include/__system_error/error_code.h (+5-5)
- (modified) libcxx/include/__system_error/error_condition.h (+4-4)
- (modified) libcxx/include/__system_error/system_error.h (+1-1)
- (modified) libcxx/include/stdexcept (+2-2)
- (added) libcxx/test/libcxx/diagnostics/syserr/nodiscard.verify.cpp (+108)
- (modified) libcxx/test/libcxx/language.support/nodiscard.verify.cpp (+40-1)
``````````diff
diff --git a/libcxx/include/__exception/exception.h b/libcxx/include/__exception/exception.h
index 161cc49979e4a..ddc34b0fa8fa1 100644
--- a/libcxx/include/__exception/exception.h
+++ b/libcxx/include/__exception/exception.h
@@ -54,7 +54,9 @@ class exception { // base of all library exceptions
virtual ~exception() _NOEXCEPT {}
- virtual char const* what() const _NOEXCEPT { return __data_._What ? __data_._What : "Unknown exception"; }
+ [[__nodiscard__]] virtual char const* what() const _NOEXCEPT {
+ return __data_._What ? __data_._What : "Unknown exception";
+ }
private:
__std_exception_data __data_;
@@ -76,7 +78,7 @@ class _LIBCPP_EXPORTED_FROM_ABI exception {
_LIBCPP_HIDE_FROM_ABI exception& operator=(const exception&) _NOEXCEPT = default;
virtual ~exception() _NOEXCEPT;
- virtual const char* what() const _NOEXCEPT;
+ [[__nodiscard__]] virtual const char* what() const _NOEXCEPT;
};
class _LIBCPP_EXPORTED_FROM_ABI bad_exception : public exception {
@@ -85,7 +87,7 @@ class _LIBCPP_EXPORTED_FROM_ABI bad_exception : public exception {
_LIBCPP_HIDE_FROM_ABI bad_exception(const bad_exception&) _NOEXCEPT = default;
_LIBCPP_HIDE_FROM_ABI bad_exception& operator=(const bad_exception&) _NOEXCEPT = default;
~bad_exception() _NOEXCEPT override;
- const char* what() const _NOEXCEPT override;
+ [[__nodiscard__]] const char* what() const _NOEXCEPT override;
};
#endif // !_LIBCPP_ABI_VCRUNTIME
diff --git a/libcxx/include/__exception/nested_exception.h b/libcxx/include/__exception/nested_exception.h
index dc3266a27cdfd..dd84efbccde88 100644
--- a/libcxx/include/__exception/nested_exception.h
+++ b/libcxx/include/__exception/nested_exception.h
@@ -40,7 +40,7 @@ class _LIBCPP_EXPORTED_FROM_ABI nested_exception {
// access functions
[[__noreturn__]] void rethrow_nested() const;
- _LIBCPP_HIDE_FROM_ABI exception_ptr nested_ptr() const _NOEXCEPT { return __ptr_; }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI exception_ptr nested_ptr() const _NOEXCEPT { return __ptr_; }
};
template <class _Tp>
diff --git a/libcxx/include/__exception/operations.h b/libcxx/include/__exception/operations.h
index 29d5c698a96db..2b93ad260c30b 100644
--- a/libcxx/include/__exception/operations.h
+++ b/libcxx/include/__exception/operations.h
@@ -20,22 +20,22 @@ _LIBCPP_BEGIN_UNVERSIONED_NAMESPACE_STD
defined(_LIBCPP_BUILDING_LIBRARY)
using unexpected_handler = void (*)();
_LIBCPP_EXPORTED_FROM_ABI unexpected_handler set_unexpected(unexpected_handler) _NOEXCEPT;
-_LIBCPP_EXPORTED_FROM_ABI unexpected_handler get_unexpected() _NOEXCEPT;
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI unexpected_handler get_unexpected() _NOEXCEPT;
[[__noreturn__]] _LIBCPP_EXPORTED_FROM_ABI void unexpected();
#endif
using terminate_handler = void (*)();
_LIBCPP_EXPORTED_FROM_ABI terminate_handler set_terminate(terminate_handler) _NOEXCEPT;
-_LIBCPP_EXPORTED_FROM_ABI terminate_handler get_terminate() _NOEXCEPT;
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI terminate_handler get_terminate() _NOEXCEPT;
#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION)
-_LIBCPP_EXPORTED_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 bool uncaught_exception() _NOEXCEPT;
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 bool uncaught_exception() _NOEXCEPT;
#endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION)
-_LIBCPP_EXPORTED_FROM_ABI int uncaught_exceptions() _NOEXCEPT;
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI int uncaught_exceptions() _NOEXCEPT;
class _LIBCPP_EXPORTED_FROM_ABI exception_ptr;
-_LIBCPP_EXPORTED_FROM_ABI exception_ptr current_exception() _NOEXCEPT;
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI exception_ptr current_exception() _NOEXCEPT;
[[__noreturn__]] _LIBCPP_EXPORTED_FROM_ABI void rethrow_exception(exception_ptr);
_LIBCPP_END_UNVERSIONED_NAMESPACE_STD
diff --git a/libcxx/include/__system_error/error_category.h b/libcxx/include/__system_error/error_category.h
index 191f4d83a90c0..7f7c7355c7e7f 100644
--- a/libcxx/include/__system_error/error_category.h
+++ b/libcxx/include/__system_error/error_category.h
@@ -37,11 +37,11 @@ class _LIBCPP_EXPORTED_FROM_ABI error_category {
error_category(const error_category&) = delete;
error_category& operator=(const error_category&) = delete;
- virtual const char* name() const _NOEXCEPT = 0;
- virtual error_condition default_error_condition(int __ev) const _NOEXCEPT;
- virtual bool equivalent(int __code, const error_condition& __condition) const _NOEXCEPT;
- virtual bool equivalent(const error_code& __code, int __condition) const _NOEXCEPT;
- virtual string message(int __ev) const = 0;
+ [[__nodiscard__]] virtual const char* name() const _NOEXCEPT = 0;
+ [[__nodiscard__]] virtual error_condition default_error_condition(int __ev) const _NOEXCEPT;
+ [[__nodiscard__]] virtual bool equivalent(int __code, const error_condition& __condition) const _NOEXCEPT;
+ [[__nodiscard__]] virtual bool equivalent(const error_code& __code, int __condition) const _NOEXCEPT;
+ [[__nodiscard__]] virtual string message(int __ev) const = 0;
_LIBCPP_HIDE_FROM_ABI bool operator==(const error_category& __rhs) const _NOEXCEPT { return this == &__rhs; }
@@ -67,8 +67,8 @@ class _LIBCPP_HIDDEN __do_message : public error_category {
string message(int __ev) const override;
};
-[[__gnu__::__const__]] _LIBCPP_EXPORTED_FROM_ABI const error_category& generic_category() _NOEXCEPT;
-[[__gnu__::__const__]] _LIBCPP_EXPORTED_FROM_ABI const error_category& system_category() _NOEXCEPT;
+[[__gnu__::__const__]] [[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI const error_category& generic_category() _NOEXCEPT;
+[[__gnu__::__const__]] [[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI const error_category& system_category() _NOEXCEPT;
_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/__system_error/error_code.h b/libcxx/include/__system_error/error_code.h
index f6ea40d6efcb9..e904376939753 100644
--- a/libcxx/include/__system_error/error_code.h
+++ b/libcxx/include/__system_error/error_code.h
@@ -71,20 +71,20 @@ class _LIBCPP_EXPORTED_FROM_ABI error_code {
__cat_ = &system_category();
}
- _LIBCPP_HIDE_FROM_ABI int value() const _NOEXCEPT { return __val_; }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI int value() const _NOEXCEPT { return __val_; }
- _LIBCPP_HIDE_FROM_ABI const error_category& category() const _NOEXCEPT { return *__cat_; }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const error_category& category() const _NOEXCEPT { return *__cat_; }
- _LIBCPP_HIDE_FROM_ABI error_condition default_error_condition() const _NOEXCEPT {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI error_condition default_error_condition() const _NOEXCEPT {
return __cat_->default_error_condition(__val_);
}
- string message() const;
+ [[__nodiscard__]] string message() const;
_LIBCPP_HIDE_FROM_ABI explicit operator bool() const _NOEXCEPT { return __val_ != 0; }
};
-inline _LIBCPP_HIDE_FROM_ABI error_code make_error_code(errc __e) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI error_code make_error_code(errc __e) _NOEXCEPT {
return error_code(static_cast<int>(__e), generic_category());
}
diff --git a/libcxx/include/__system_error/error_condition.h b/libcxx/include/__system_error/error_condition.h
index 34819f4b6de4c..be7deaba0444c 100644
--- a/libcxx/include/__system_error/error_condition.h
+++ b/libcxx/include/__system_error/error_condition.h
@@ -80,15 +80,15 @@ class _LIBCPP_EXPORTED_FROM_ABI error_condition {
__cat_ = &generic_category();
}
- _LIBCPP_HIDE_FROM_ABI int value() const _NOEXCEPT { return __val_; }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI int value() const _NOEXCEPT { return __val_; }
- _LIBCPP_HIDE_FROM_ABI const error_category& category() const _NOEXCEPT { return *__cat_; }
- string message() const;
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const error_category& category() const _NOEXCEPT { return *__cat_; }
+ [[__nodiscard__]] string message() const;
_LIBCPP_HIDE_FROM_ABI explicit operator bool() const _NOEXCEPT { return __val_ != 0; }
};
-inline _LIBCPP_HIDE_FROM_ABI error_condition make_error_condition(errc __e) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI error_condition make_error_condition(errc __e) _NOEXCEPT {
return error_condition(static_cast<int>(__e), generic_category());
}
diff --git a/libcxx/include/__system_error/system_error.h b/libcxx/include/__system_error/system_error.h
index 36ccf94cc010d..74427d8f0bf9b 100644
--- a/libcxx/include/__system_error/system_error.h
+++ b/libcxx/include/__system_error/system_error.h
@@ -36,7 +36,7 @@ class _LIBCPP_EXPORTED_FROM_ABI system_error : public runtime_error {
_LIBCPP_HIDE_FROM_ABI system_error(const system_error&) _NOEXCEPT = default;
~system_error() _NOEXCEPT override;
- _LIBCPP_HIDE_FROM_ABI const error_code& code() const _NOEXCEPT { return __ec_; }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const error_code& code() const _NOEXCEPT { return __ec_; }
};
// __ev is expected to be an error in the generic_category domain (e.g. from
diff --git a/libcxx/include/stdexcept b/libcxx/include/stdexcept
index 85e11629bd6e3..d01de5c46211c 100644
--- a/libcxx/include/stdexcept
+++ b/libcxx/include/stdexcept
@@ -91,7 +91,7 @@ public:
~logic_error() _NOEXCEPT override;
- const char* what() const _NOEXCEPT override;
+ [[__nodiscard__]] const char* what() const _NOEXCEPT override;
# else
public:
@@ -115,7 +115,7 @@ public:
~runtime_error() _NOEXCEPT override;
- const char* what() const _NOEXCEPT override;
+ [[__nodiscard__]] const char* what() const _NOEXCEPT override;
# else
public:
diff --git a/libcxx/test/libcxx/diagnostics/syserr/nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/syserr/nodiscard.verify.cpp
new file mode 100644
index 0000000000000..26565a1ecdd10
--- /dev/null
+++ b/libcxx/test/libcxx/diagnostics/syserr/nodiscard.verify.cpp
@@ -0,0 +1,108 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// Check that functions are marked [[nodiscard]]
+
+#include <stdexcept>
+#include <system_error>
+
+void test() {
+ { // <stdexcept>
+ std::logic_error le("logic error");
+ le.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::runtime_error re("runtime error");
+ re.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::domain_error de("domain error");
+ de.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::invalid_argument ia("invalid argument");
+ ia.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::length_error lerr("length error");
+ lerr.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::out_of_range oor("out of range");
+ oor.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::range_error rerr("range error");
+ rerr.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::overflow_error oferr("overflow error");
+ oferr.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::underflow_error uferr("underflow error");
+ uferr.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ }
+ { // <system_error>
+ {
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::generic_category();
+
+ const std::error_category& ec = std::generic_category();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.name();
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.default_error_condition(94);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.equivalent(94, ec.default_error_condition(82));
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.equivalent(std::error_code(49, ec), 94);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.message(82);
+ }
+ {
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::system_category();
+
+ const std::error_category& ec = std::system_category();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.name();
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.default_error_condition(94);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.equivalent(94, ec.default_error_condition(82));
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.equivalent(std::error_code(49, ec), 94);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.message(82);
+ }
+ {
+ std::error_code ec;
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.value();
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.category();
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.default_error_condition();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.message();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::make_error_code(std::errc::invalid_argument);
+ }
+ {
+ std::error_condition ec;
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.value();
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.category();
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ec.message();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::make_error_condition(std::errc::invalid_argument);
+ }
+ }
+}
diff --git a/libcxx/test/libcxx/language.support/nodiscard.verify.cpp b/libcxx/test/libcxx/language.support/nodiscard.verify.cpp
index b87b04ad9f1ef..40dbe5c90afee 100644
--- a/libcxx/test/libcxx/language.support/nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/language.support/nodiscard.verify.cpp
@@ -6,12 +6,15 @@
//
//===----------------------------------------------------------------------===//
-// UNSUPPORTED: c++03
+// ADDITIONAL_COMPILE_FLAGS: -Wno-deprecated
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION
// Check that functions are marked [[nodiscard]]
#include <compare>
#include <coroutine>
+#include <exception>
#include <functional>
#include <initializer_list>
@@ -81,6 +84,41 @@ void test() {
}
#endif
+ { // <exception>
+ {
+ std::bad_exception bex;
+
+ bex.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ }
+ {
+ std::exception ex;
+
+ ex.what(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ }
+ {
+ std::nested_exception nex;
+
+ nex.nested_ptr(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ }
+
+#if TEST_STD_VER <= 14
+ std::get_unexpected(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
+
+ std::get_terminate(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+#if _LIBCPP_STD_VER <= 17
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::uncaught_exception();
+#endif
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::uncaught_exceptions();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::current_exception();
+ }
+
+#if TEST_STD_VER >= 11
{ // <initializer_list>
std::initializer_list<int> il{94, 82, 49};
@@ -88,4 +126,5 @@ void test() {
il.begin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
il.end(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
}
+#endif
}
``````````
</details>
https://github.com/llvm/llvm-project/pull/170837
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