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Re: [PATCH] Add [[nodiscard]] attribute to C++17 components
- From: Jonathan Wakely <jwakely at redhat dot com>
- To: libstdc++ at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Thu, 23 Nov 2017 22:51:54 +0000
- Subject: Re: [PATCH] Add [[nodiscard]] attribute to C++17 components
- Authentication-results: sourceware.org; auth=none
- References: <20171123224048.GA24885@redhat.com>
On 23/11/17 22:40 +0000, Jonathan Wakely wrote:
C++17 added the [[nodiscard]] attribute, similar to GCC's
warn_unused_result. The C++2a draft requires it to be used in several
places. This patch adds it where required on components which are new
to C++17, which are still experimental and so I'm changing them in
stage 3.
This adds the other [[nodiscard]] attributes required by C++2a, but
using [[__nodiscard__]] so it can be enabled in C++11 and C++14, where
nodiscard is not a reserved name.
I don't plan to commit this until stage 1 (and don't have tests for it
yet anyway).
commit 9159c87e19510662eecfeadf8facbe68b40ac2c7
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Thu Nov 23 22:42:45 2017 +0000
Add more nodiscard attributes
diff --git a/libstdc++-v3/include/bits/alloc_traits.h b/libstdc++-v3/include/bits/alloc_traits.h
index 86a48594ea1..ba75f33726d 100644
--- a/libstdc++-v3/include/bits/alloc_traits.h
+++ b/libstdc++-v3/include/bits/alloc_traits.h
@@ -296,7 +296,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*
* Calls @c a.allocate(n)
*/
- static pointer
+ [[__nodiscard__]] static pointer
allocate(_Alloc& __a, size_type __n)
{ return __a.allocate(__n); }
@@ -311,7 +311,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* Returns <tt> a.allocate(n, hint) </tt> if that expression is
* well-formed, otherwise returns @c a.allocate(n)
*/
- static pointer
+ [[__nodiscard__]] static pointer
allocate(_Alloc& __a, size_type __n, const_void_pointer __hint)
{ return _S_allocate(__a, __n, __hint, 0); }
diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index a4b81137571..bec6e902076 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -1008,7 +1008,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
* Returns true if the %string is empty. Equivalent to
* <code>*this == ""</code>.
*/
- bool
+ _GLIBCXX_NODISCARD bool
empty() const _GLIBCXX_NOEXCEPT
{ return this->size() == 0; }
diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 21e3fbb2741..cfa2534e3f5 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -99,6 +99,11 @@
# define _GLIBCXX_ABI_TAG_CXX11 __attribute ((__abi_tag__ ("cxx11")))
#endif
+#if __cplusplus >= 201103L
+# define _GLIBCXX_NODISCARD [[__nodiscard__]]
+#else
+# define _GLIBCXX_NODISCARD
+#endif
#if __cplusplus
diff --git a/libstdc++-v3/include/bits/forward_list.h b/libstdc++-v3/include/bits/forward_list.h
index 96494cc20de..b8eb9f3d6fe 100644
--- a/libstdc++-v3/include/bits/forward_list.h
+++ b/libstdc++-v3/include/bits/forward_list.h
@@ -756,7 +756,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
* Returns true if the %forward_list is empty. (Thus begin() would
* equal end().)
*/
- bool
+ [[__nodiscard__]] bool
empty() const noexcept
{ return this->_M_impl._M_head._M_next == 0; }
diff --git a/libstdc++-v3/include/bits/regex.h b/libstdc++-v3/include/bits/regex.h
index 32e7159eec9..4866cb42b00 100644
--- a/libstdc++-v3/include/bits/regex.h
+++ b/libstdc++-v3/include/bits/regex.h
@@ -1631,7 +1631,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
* @retval true The %match_results object is empty.
* @retval false The %match_results object is not empty.
*/
- bool
+ [[__nodiscard__]] bool
empty() const
{ return size() == 0; }
diff --git a/libstdc++-v3/include/bits/stl_bvector.h b/libstdc++-v3/include/bits/stl_bvector.h
index ac548846b0e..80a54e78ff3 100644
--- a/libstdc++-v3/include/bits/stl_bvector.h
+++ b/libstdc++-v3/include/bits/stl_bvector.h
@@ -873,7 +873,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
{ return size_type(const_iterator(this->_M_impl._M_end_addr(), 0)
- begin()); }
- bool
+ _GLIBCXX_NODISCARD bool
empty() const _GLIBCXX_NOEXCEPT
{ return begin() == end(); }
diff --git a/libstdc++-v3/include/bits/stl_deque.h b/libstdc++-v3/include/bits/stl_deque.h
index 93c82ca8909..ae170623247 100644
--- a/libstdc++-v3/include/bits/stl_deque.h
+++ b/libstdc++-v3/include/bits/stl_deque.h
@@ -1363,7 +1363,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
* Returns true if the %deque is empty. (Thus begin() would
* equal end().)
*/
- bool
+ _GLIBCXX_NODISCARD bool
empty() const _GLIBCXX_NOEXCEPT
{ return this->_M_impl._M_finish == this->_M_impl._M_start; }
diff --git a/libstdc++-v3/include/bits/stl_list.h b/libstdc++-v3/include/bits/stl_list.h
index 8ed97f7c8b0..93378139871 100644
--- a/libstdc++-v3/include/bits/stl_list.h
+++ b/libstdc++-v3/include/bits/stl_list.h
@@ -1058,7 +1058,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
* Returns true if the %list is empty. (Thus begin() would equal
* end().)
*/
- bool
+ _GLIBCXX_NODISCARD bool
empty() const _GLIBCXX_NOEXCEPT
{ return this->_M_impl._M_node._M_next == &this->_M_impl._M_node; }
diff --git a/libstdc++-v3/include/bits/stl_map.h b/libstdc++-v3/include/bits/stl_map.h
index bec6c47c086..fec8d81c183 100644
--- a/libstdc++-v3/include/bits/stl_map.h
+++ b/libstdc++-v3/include/bits/stl_map.h
@@ -459,7 +459,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
/** Returns true if the %map is empty. (Thus begin() would equal
* end().)
*/
- bool
+ _GLIBCXX_NODISCARD bool
empty() const _GLIBCXX_NOEXCEPT
{ return _M_t.empty(); }
diff --git a/libstdc++-v3/include/bits/stl_multimap.h b/libstdc++-v3/include/bits/stl_multimap.h
index 24ac4a3c186..bce79c2d587 100644
--- a/libstdc++-v3/include/bits/stl_multimap.h
+++ b/libstdc++-v3/include/bits/stl_multimap.h
@@ -452,7 +452,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
// capacity
/** Returns true if the %multimap is empty. */
- bool
+ _GLIBCXX_NODISCARD bool
empty() const _GLIBCXX_NOEXCEPT
{ return _M_t.empty(); }
diff --git a/libstdc++-v3/include/bits/stl_multiset.h b/libstdc++-v3/include/bits/stl_multiset.h
index ff7d3dca586..aa147467c36 100644
--- a/libstdc++-v3/include/bits/stl_multiset.h
+++ b/libstdc++-v3/include/bits/stl_multiset.h
@@ -406,7 +406,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
#endif
/// Returns true if the %set is empty.
- bool
+ _GLIBCXX_NODISCARD bool
empty() const _GLIBCXX_NOEXCEPT
{ return _M_t.empty(); }
diff --git a/libstdc++-v3/include/bits/stl_queue.h b/libstdc++-v3/include/bits/stl_queue.h
index c49f371fbc8..60a2f0e281e 100644
--- a/libstdc++-v3/include/bits/stl_queue.h
+++ b/libstdc++-v3/include/bits/stl_queue.h
@@ -185,7 +185,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* Returns true if the %queue is empty.
*/
- bool
+ _GLIBCXX_NODISCARD bool
empty() const
{ return c.empty(); }
@@ -563,7 +563,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* Returns true if the %queue is empty.
*/
- bool
+ _GLIBCXX_NODISCARD bool
empty() const
{ return c.empty(); }
diff --git a/libstdc++-v3/include/bits/stl_set.h b/libstdc++-v3/include/bits/stl_set.h
index e07d78124eb..9f566a2a6eb 100644
--- a/libstdc++-v3/include/bits/stl_set.h
+++ b/libstdc++-v3/include/bits/stl_set.h
@@ -410,7 +410,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
#endif
/// Returns true if the %set is empty.
- bool
+ _GLIBCXX_NODISCARD bool
empty() const _GLIBCXX_NOEXCEPT
{ return _M_t.empty(); }
diff --git a/libstdc++-v3/include/bits/stl_stack.h b/libstdc++-v3/include/bits/stl_stack.h
index 5f2b4ab4486..d115134d0fe 100644
--- a/libstdc++-v3/include/bits/stl_stack.h
+++ b/libstdc++-v3/include/bits/stl_stack.h
@@ -181,7 +181,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* Returns true if the %stack is empty.
*/
- bool
+ _GLIBCXX_NODISCARD bool
empty() const
{ return c.empty(); }
diff --git a/libstdc++-v3/include/bits/stl_vector.h b/libstdc++-v3/include/bits/stl_vector.h
index aeeba820020..75f58e525ae 100644
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -890,7 +890,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
* Returns true if the %vector is empty. (Thus begin() would
* equal end().)
*/
- bool
+ _GLIBCXX_NODISCARD bool
empty() const _GLIBCXX_NOEXCEPT
{ return begin() == end(); }
diff --git a/libstdc++-v3/include/bits/unordered_map.h b/libstdc++-v3/include/bits/unordered_map.h
index cb5bcb89a16..3400aed47e9 100644
--- a/libstdc++-v3/include/bits/unordered_map.h
+++ b/libstdc++-v3/include/bits/unordered_map.h
@@ -300,7 +300,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
// size and capacity:
/// Returns true if the %unordered_map is empty.
- bool
+ [[__nodiscard__]] bool
empty() const noexcept
{ return _M_h.empty(); }
@@ -1433,7 +1433,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
// size and capacity:
/// Returns true if the %unordered_multimap is empty.
- bool
+ [[__nodiscard__]] bool
empty() const noexcept
{ return _M_h.empty(); }
diff --git a/libstdc++-v3/include/bits/unordered_set.h b/libstdc++-v3/include/bits/unordered_set.h
index 550548c42db..279b61ce3d6 100644
--- a/libstdc++-v3/include/bits/unordered_set.h
+++ b/libstdc++-v3/include/bits/unordered_set.h
@@ -294,7 +294,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
// size and capacity:
/// Returns true if the %unordered_set is empty.
- bool
+ [[__nodiscard__]] bool
empty() const noexcept
{ return _M_h.empty(); }
@@ -1091,7 +1091,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
// size and capacity:
/// Returns true if the %unordered_multiset is empty.
- bool
+ [[__nodiscard__]] bool
empty() const noexcept
{ return _M_h.empty(); }
diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h b/libstdc++-v3/include/experimental/bits/fs_path.h
index 3e9bc6357af..81c6ac44dd1 100644
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -359,7 +359,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
// query
- bool empty() const noexcept { return _M_pathname.empty(); }
+ [[__nodiscard__]] bool
+ empty() const noexcept { return _M_pathname.empty(); }
+
bool has_root_name() const;
bool has_root_directory() const;
bool has_root_path() const;
diff --git a/libstdc++-v3/include/experimental/string_view b/libstdc++-v3/include/experimental/string_view
index 8eaf9ec3d96..bbe7a46791f 100644
--- a/libstdc++-v3/include/experimental/string_view
+++ b/libstdc++-v3/include/experimental/string_view
@@ -169,7 +169,7 @@ inline namespace fundamentals_v1
/ sizeof(value_type) / 4;
}
- constexpr bool
+ [[__nodiscard__]] constexpr bool
empty() const noexcept
{ return this->_M_len == 0; }
diff --git a/libstdc++-v3/include/ext/new_allocator.h b/libstdc++-v3/include/ext/new_allocator.h
index e1e152c4bf0..de18cc7a4f8 100644
--- a/libstdc++-v3/include/ext/new_allocator.h
+++ b/libstdc++-v3/include/ext/new_allocator.h
@@ -95,7 +95,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// NB: __n is permitted to be 0. The C++ standard says nothing
// about what the return value is when __n == 0.
- pointer
+ _GLIBCXX_NODISCARD pointer
allocate(size_type __n, const void* = static_cast<const void*>(0))
{
if (__n > this->max_size())
diff --git a/libstdc++-v3/include/std/array b/libstdc++-v3/include/std/array
index 01f7100bae0..329d3b33a68 100644
--- a/libstdc++-v3/include/std/array
+++ b/libstdc++-v3/include/std/array
@@ -177,7 +177,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
constexpr size_type
max_size() const noexcept { return _Nm; }
- constexpr bool
+ [[__nodiscard__]] constexpr bool
empty() const noexcept { return size() == 0; }
// Element access.
diff --git a/libstdc++-v3/include/std/future b/libstdc++-v3/include/std/future
index d9d446bc2f6..6b51499526a 100644
--- a/libstdc++-v3/include/std/future
+++ b/libstdc++-v3/include/std/future
@@ -1708,7 +1708,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// async
template<typename _Fn, typename... _Args>
- future<__async_result_of<_Fn, _Args...>>
+ [[__nodiscard__]] future<__async_result_of<_Fn, _Args...>>
async(launch __policy, _Fn&& __fn, _Args&&... __args)
{
std::shared_ptr<__future_base::_State_base> __state;
@@ -1741,7 +1741,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// async, potential overload
template<typename _Fn, typename... _Args>
- inline future<__async_result_of<_Fn, _Args...>>
+ [[__nodiscard__]] inline future<__async_result_of<_Fn, _Args...>>
async(_Fn&& __fn, _Args&&... __args)
{
return std::async(launch::async|launch::deferred,
diff --git a/libstdc++-v3/include/std/scoped_allocator b/libstdc++-v3/include/std/scoped_allocator
index 725f5471444..ee955e9fa90 100644
--- a/libstdc++-v3/include/std/scoped_allocator
+++ b/libstdc++-v3/include/std/scoped_allocator
@@ -335,10 +335,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
const outer_allocator_type& outer_allocator() const noexcept
{ return static_cast<const _OuterAlloc&>(*this); }
- pointer allocate(size_type __n)
+ [[__nodiscard__]] pointer
+ allocate(size_type __n)
{ return __traits::allocate(outer_allocator(), __n); }
- pointer allocate(size_type __n, const_void_pointer __hint)
+ [[__nodiscard__]] pointer
+ allocate(size_type __n, const_void_pointer __hint)
{ return __traits::allocate(outer_allocator(), __n, __hint); }
void deallocate(pointer __p, size_type __n)
diff --git a/libstdc++-v3/libsupc++/new b/libstdc++-v3/libsupc++/new
index 795b33c4e6a..cc4cb294be7 100644
--- a/libstdc++-v3/libsupc++/new
+++ b/libstdc++-v3/libsupc++/new
@@ -117,8 +117,10 @@ namespace std
* Placement new and delete signatures (take a memory address argument,
* does nothing) may not be replaced by a user's program.
*/
+_GLIBCXX_NODISCARD
void* operator new(std::size_t) _GLIBCXX_THROW (std::bad_alloc)
__attribute__((__externally_visible__));
+_GLIBCXX_NODISCARD
void* operator new[](std::size_t) _GLIBCXX_THROW (std::bad_alloc)
__attribute__((__externally_visible__));
void operator delete(void*) _GLIBCXX_USE_NOEXCEPT
@@ -131,8 +133,10 @@ void operator delete(void*, std::size_t) _GLIBCXX_USE_NOEXCEPT
void operator delete[](void*, std::size_t) _GLIBCXX_USE_NOEXCEPT
__attribute__((__externally_visible__));
#endif
+_GLIBCXX_NODISCARD
void* operator new(std::size_t, const std::nothrow_t&) _GLIBCXX_USE_NOEXCEPT
__attribute__((__externally_visible__));
+_GLIBCXX_NODISCARD
void* operator new[](std::size_t, const std::nothrow_t&) _GLIBCXX_USE_NOEXCEPT
__attribute__((__externally_visible__));
void operator delete(void*, const std::nothrow_t&) _GLIBCXX_USE_NOEXCEPT
@@ -140,16 +144,20 @@ void operator delete(void*, const std::nothrow_t&) _GLIBCXX_USE_NOEXCEPT
void operator delete[](void*, const std::nothrow_t&) _GLIBCXX_USE_NOEXCEPT
__attribute__((__externally_visible__));
#if __cpp_aligned_new
+_GLIBCXX_NODISCARD
void* operator new(std::size_t, std::align_val_t)
__attribute__((__externally_visible__));
+_GLIBCXX_NODISCARD
void* operator new(std::size_t, std::align_val_t, const std::nothrow_t&)
_GLIBCXX_USE_NOEXCEPT __attribute__((__externally_visible__));
void operator delete(void*, std::align_val_t)
_GLIBCXX_USE_NOEXCEPT __attribute__((__externally_visible__));
void operator delete(void*, std::align_val_t, const std::nothrow_t&)
_GLIBCXX_USE_NOEXCEPT __attribute__((__externally_visible__));
+_GLIBCXX_NODISCARD
void* operator new[](std::size_t, std::align_val_t)
__attribute__((__externally_visible__));
+_GLIBCXX_NODISCARD
void* operator new[](std::size_t, std::align_val_t, const std::nothrow_t&)
_GLIBCXX_USE_NOEXCEPT __attribute__((__externally_visible__));
void operator delete[](void*, std::align_val_t)
@@ -165,8 +173,10 @@ void operator delete[](void*, std::size_t, std::align_val_t)
#endif // __cpp_aligned_new
// Default placement versions of operator new.
+_GLIBCXX_NODISCARD
inline void* operator new(std::size_t, void* __p) _GLIBCXX_USE_NOEXCEPT
{ return __p; }
+_GLIBCXX_NODISCARD
inline void* operator new[](std::size_t, void* __p) _GLIBCXX_USE_NOEXCEPT
{ return __p; }
diff --git a/libstdc++-v3/testsuite/17_intro/headers/c++1998/all_attributes.cc b/libstdc++-v3/testsuite/17_intro/headers/c++1998/all_attributes.cc
index 6d6d7980396..8090cce8b9c 100644
--- a/libstdc++-v3/testsuite/17_intro/headers/c++1998/all_attributes.cc
+++ b/libstdc++-v3/testsuite/17_intro/headers/c++1998/all_attributes.cc
@@ -22,6 +22,7 @@
// Don't test 'const' because it is reserved anyway.
#define abi_tag 1
#define always_inline 1
+#define nodiscard 1
#ifndef __APPLE__
// darwin headers use these, see PR 64883
# define deprecated 1
diff --git a/libstdc++-v3/testsuite/17_intro/headers/c++2011/all_attributes.cc b/libstdc++-v3/testsuite/17_intro/headers/c++2011/all_attributes.cc
index 415ece0296f..809f001a384 100644
--- a/libstdc++-v3/testsuite/17_intro/headers/c++2011/all_attributes.cc
+++ b/libstdc++-v3/testsuite/17_intro/headers/c++2011/all_attributes.cc
@@ -22,6 +22,7 @@
// Don't test 'const' and 'noreturn' because they are reserved anyway.
#define abi_tag 1
#define always_inline 1
+#define nodiscard 1
#ifndef __APPLE__
// darwin headers use these, see PR 64883
# define visibility 1
diff --git a/libstdc++-v3/testsuite/17_intro/headers/c++2014/all_attributes.cc b/libstdc++-v3/testsuite/17_intro/headers/c++2014/all_attributes.cc
index d4ef52412a3..70533610a1f 100644
--- a/libstdc++-v3/testsuite/17_intro/headers/c++2014/all_attributes.cc
+++ b/libstdc++-v3/testsuite/17_intro/headers/c++2014/all_attributes.cc
@@ -22,6 +22,7 @@
// Don't test 'const' and 'noreturn' because they are reserved anyway.
#define abi_tag 1
#define always_inline 1
+#define nodiscard 1
#ifndef __APPLE__
// darwin headers use these, see PR 64883
# define deprecated 1