libstdc++: Move [[nodiscard]] attributes again [PR101782]

Where I moved these nodiscard attributes to made them apply to the
function type, not to the function. This meant they no longer generated
the desired -Wunused-result warnings, and were ill-formed with Clang
(but only a pedwarn with GCC).

Clang also detected ill-formed attributes in <queue> which this fixes.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	PR libstdc++/101782
	* include/bits/ranges_base.h (ranges::begin, ranges::end)
	(ranges::rbegin, ranges::rend, ranges::size, ranges::ssize)
	(ranges::empty, ranges::data): Move attribute after the
	declarator-id instead of at the end of the declarator.
	* include/bits/stl_iterator.h (__gnu_cxx::__normal_iterator):
	Move attributes back to the start of the function declarator,
	but move the requires-clause to the end.
	(common_iterator): Move attribute after the declarator-id.
	* include/bits/stl_queue.h (queue): Remove ill-formed attributes
	from friend declaration that are not definitions.
	* include/std/ranges (views::all, views::filter)
	(views::transform, views::take, views::take_while,
	views::drop) (views::drop_while, views::join,
	views::lazy_split) (views::split, views::counted,
	views::common, views::reverse) (views::elements): Move
	attributes after the declarator-id.

4 files changed, 33 insertions, 60 deletions

diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
index 1dac968..49c7d9c 100644
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -111,8 +111,7 @@ namespace ranges
 	requires is_array_v<remove_reference_t<_Tp>> || __member_begin<_Tp>
 	  || __adl_begin<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
 	  if constexpr (is_array_v<remove_reference_t<_Tp>>)
 	    {
@@ -163,8 +162,7 @@ namespace ranges
 	requires is_bounded_array_v<remove_reference_t<_Tp>>
 	  || __member_end<_Tp> || __adl_end<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
 	  if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
 	    {
@@ -268,9 +266,8 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires __member_rbegin<_Tp> || __adl_rbegin<_Tp> || __reversable<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const
+	operator()[[nodiscard]](_Tp&& __t) const
 	noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
 	{
 	  if constexpr (__member_rbegin<_Tp>)
 	    return __t.rbegin();
@@ -327,9 +324,8 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires __member_rend<_Tp> || __adl_rend<_Tp> || __reversable<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const
+	operator()[[nodiscard]](_Tp&& __t) const
 	noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
 	{
 	  if constexpr (__member_rend<_Tp>)
 	    return __t.rend();
@@ -417,8 +413,7 @@ namespace ranges
 	requires is_bounded_array_v<remove_reference_t<_Tp>>
 	  || __member_size<_Tp> || __adl_size<_Tp> || __sentinel_size<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
 	  if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
 	    return extent_v<remove_reference_t<_Tp>>;
@@ -438,8 +433,7 @@ namespace ranges
       template<typename _Tp>
 	requires requires (_Tp& __t) { _Size{}(__t); }
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(noexcept(_Size{}(__t)))
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(noexcept(_Size{}(__t)))
 	{
 	  auto __size = _Size{}(__t);
 	  using __size_type = decltype(__size);
@@ -498,8 +492,7 @@ namespace ranges
 	requires __member_empty<_Tp> || __size0_empty<_Tp>
 	  || __eq_iter_empty<_Tp>
 	constexpr bool
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
 	  if constexpr (__member_empty<_Tp>)
 	    return bool(__t.empty());
@@ -540,8 +533,7 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires __member_data<_Tp> || __begin_data<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp>())
 	{
 	  if constexpr (__member_data<_Tp>)
 	    return __t.data();
diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 053ae41..c5b0240 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1118,21 +1118,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __cpp_lib_three_way_comparison
   template<typename _IteratorL, typename _IteratorR, typename _Container>
-    requires requires (_IteratorL __lhs, _IteratorR __rhs)
-    { { __lhs == __rhs } -> std::convertible_to<bool>; }
+    [[nodiscard]]
     constexpr bool
     operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
     noexcept(noexcept(__lhs.base() == __rhs.base()))
-    [[nodiscard]]
+    requires requires {
+      { __lhs.base() == __rhs.base() } -> std::convertible_to<bool>;
+    }
     { return __lhs.base() == __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    [[nodiscard]]
     constexpr std::__detail::__synth3way_t<_IteratorR, _IteratorL>
     operator<=>(const __normal_iterator<_IteratorL, _Container>& __lhs,
 		const __normal_iterator<_IteratorR, _Container>& __rhs)
     noexcept(noexcept(std::__detail::__synth3way(__lhs.base(), __rhs.base())))
-    [[nodiscard]]
     { return std::__detail::__synth3way(__lhs.base(), __rhs.base()); }
 #else
    // Forward iterator requirements
@@ -1985,9 +1986,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _It2, sentinel_for<_It> _Sent2>
       requires sentinel_for<_Sent, _It2>
       friend bool
-      operator==(const common_iterator& __x,
-		 const common_iterator<_It2, _Sent2>& __y)
-      [[nodiscard]]
+      operator== [[nodiscard]] (const common_iterator& __x,
+				const common_iterator<_It2, _Sent2>& __y)
       {
 	switch(__x._M_index << 2 | __y._M_index)
 	  {
@@ -2008,9 +2008,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _It2, sentinel_for<_It> _Sent2>
       requires sentinel_for<_Sent, _It2> && equality_comparable_with<_It, _It2>
       friend bool
-      operator==(const common_iterator& __x,
-		 const common_iterator<_It2, _Sent2>& __y)
-      [[nodiscard]]
+      operator== [[nodiscard]] (const common_iterator& __x,
+				const common_iterator<_It2, _Sent2>& __y)
       {
 	switch(__x._M_index << 2 | __y._M_index)
 	  {
@@ -2032,9 +2031,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<sized_sentinel_for<_It> _It2, sized_sentinel_for<_It> _Sent2>
       requires sized_sentinel_for<_Sent, _It2>
       friend iter_difference_t<_It2>
-      operator-(const common_iterator& __x,
-		const common_iterator<_It2, _Sent2>& __y)
-      [[nodiscard]]
+      operator- [[nodiscard]] (const common_iterator& __x,
+			       const common_iterator<_It2, _Sent2>& __y)
       {
 	switch(__x._M_index << 2 | __y._M_index)
 	  {
diff --git a/libstdc++-v3/include/bits/stl_queue.h b/libstdc++-v3/include/bits/stl_queue.h
index 363868f..41ffc50 100644
--- a/libstdc++-v3/include/bits/stl_queue.h
+++ b/libstdc++-v3/include/bits/stl_queue.h
@@ -107,18 +107,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
       template<typename _Tp1, typename _Seq1>
-	_GLIBCXX_NODISCARD
 	friend bool
 	operator==(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 
       template<typename _Tp1, typename _Seq1>
-	_GLIBCXX_NODISCARD
 	friend bool
 	operator<(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 
 #if __cpp_lib_three_way_comparison
       template<typename _Tp1, three_way_comparable _Seq1>
-	[[nodiscard]]
 	friend compare_three_way_result_t<_Seq1>
 	operator<=>(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 #endif
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 71b7dc7..fb8905f 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1127,9 +1127,8 @@ namespace views::__adaptor
 	  || __detail::__can_ref_view<_Range>
 	  || __detail::__can_subrange<_Range>
 	constexpr auto
-	operator()(_Range&& __r) const
+	operator() [[nodiscard]] (_Range&& __r) const
 	noexcept(_S_noexcept<_Range>())
-	[[nodiscard]]
 	{
 	  if constexpr (view<decay_t<_Range>>)
 	    return std::forward<_Range>(__r);
@@ -1554,8 +1553,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_filter_view<_Range, _Pred>
 	constexpr auto
-	operator()(_Range&& __r, _Pred&& __p) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pred&& __p) const
 	{
 	  return filter_view(std::forward<_Range>(__r), std::forward<_Pred>(__p));
 	}
@@ -1932,8 +1930,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Fp>
 	requires __detail::__can_transform_view<_Range, _Fp>
 	constexpr auto
-	operator()(_Range&& __r, _Fp&& __f) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Fp&& __f) const
 	{
 	  return transform_view(std::forward<_Range>(__r), std::forward<_Fp>(__f));
 	}
@@ -2114,8 +2111,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Tp>
 	requires __detail::__can_take_view<_Range, _Tp>
 	constexpr auto
-	operator()(_Range&& __r, _Tp&& __n) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Tp&& __n) const
 	{
 	  return take_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
 	}
@@ -2242,8 +2238,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_take_while_view<_Range, _Pred>
 	constexpr auto
-	operator()(_Range&& __r, _Pred&& __p) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pred&& __p) const
 	{
 	  return take_while_view(std::forward<_Range>(__r), std::forward<_Pred>(__p));
 	}
@@ -2363,8 +2358,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Tp>
 	requires __detail::__can_drop_view<_Range, _Tp>
 	constexpr auto
-	operator()(_Range&& __r, _Tp&& __n) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Tp&& __n) const
 	{
 	  return drop_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
 	}
@@ -2452,8 +2446,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_drop_while_view<_Range, _Pred>
 	constexpr auto
-	operator()(_Range&& __r, _Pred&& __p) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pred&& __p) const
 	{
 	  return drop_while_view(std::forward<_Range>(__r),
 				 std::forward<_Pred>(__p));
@@ -2815,8 +2808,7 @@ namespace views::__adaptor
       template<viewable_range _Range>
 	requires __detail::__can_join_view<_Range>
 	constexpr auto
-	operator()(_Range&& __r) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r) const
 	{
 	  // _GLIBCXX_RESOLVE_LIB_DEFECTS
 	  // 3474. Nesting join_views is broken because of CTAD
@@ -3267,8 +3259,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pattern>
 	requires __detail::__can_lazy_split_view<_Range, _Pattern>
 	constexpr auto
-	operator()(_Range&& __r, _Pattern&& __f) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pattern&& __f) const
 	{
 	  return lazy_split_view(std::forward<_Range>(__r), std::forward<_Pattern>(__f));
 	}
@@ -3476,8 +3467,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pattern>
 	requires __detail::__can_split_view<_Range, _Pattern>
 	constexpr auto
-	operator()(_Range&& __r, _Pattern&& __f) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pattern&& __f) const
 	{
 	  return split_view(std::forward<_Range>(__r), std::forward<_Pattern>(__f));
 	}
@@ -3498,8 +3488,7 @@ namespace views::__adaptor
     {
       template<input_or_output_iterator _Iter>
       constexpr auto
-      operator()(_Iter __i, iter_difference_t<_Iter> __n) const
-      [[nodiscard]]
+      operator() [[nodiscard]] (_Iter __i, iter_difference_t<_Iter> __n) const
       {
 	if constexpr (random_access_iterator<_Iter>)
 	  return subrange(__i, __i + __n);
@@ -3620,8 +3609,7 @@ namespace views::__adaptor
 	requires __detail::__already_common<_Range>
 	  || __detail::__can_common_view<_Range>
 	constexpr auto
-	operator()(_Range&& __r) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r) const
 	{
 	  if constexpr (__detail::__already_common<_Range>)
 	    return views::all(std::forward<_Range>(__r));
@@ -3743,8 +3731,7 @@ namespace views::__adaptor
 	  || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
 	  || __detail::__can_reverse_view<_Range>
 	constexpr auto
-	operator()(_Range&& __r) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r) const
 	{
 	  using _Tp = remove_cvref_t<_Range>;
 	  if constexpr (__detail::__is_reverse_view<_Tp>)
@@ -4142,8 +4129,7 @@ namespace views::__adaptor
 	template<viewable_range _Range>
 	  requires __detail::__can_elements_view<_Nm, _Range>
 	  constexpr auto
-	  operator()(_Range&& __r) const
-	  [[nodiscard]]
+	  operator() [[nodiscard]] (_Range&& __r) const
 	  {
 	    return elements_view<all_t<_Range>, _Nm>{std::forward<_Range>(__r)};
 	  }