libstdc++: Add data/member for initializer_list, and remove std overloads

This implements changes section 4.6 of P3016R6, and initializer_list related
parts of 4.7 and 4.8. The change makes immediately dangling invocations of
std::begin, std::end, and std::data on braced-init list ill-formed (see
range_access_neg.cc and range_access17_neg.cc):
  auto it = std::begin({1, 2, 3});  // ILL-FORMED, it was dangling
  (it == std::end({1, 2, 3}));      // ILL-FORMED, was unspecified
  auto* ptr = std::data({1, 2, 3}); // ILL-FORMED, ptr was dangling
However, similary problemetic calls for std::rbegin, std::rend remain
well-formed (see range_access14_neg.cc), as initializer_list overloads
are preserved for these functions:
  auto rit = ranges::rbegin({1, 2, 3}); // COMPILES, dangling
  auto rend = ranges::rend({1, 2, 3});  // COMPILES, danging
Note, that non-problematic std::size({1, 2, 3}) and std::empty({1, 2, 3})
use c-array overloads, and remain well-formed.

Per paper, to keep std::data(il) and std::empty(il) well-formed, the data
and empty member are added to initializer_list.

libstdc++-v3/ChangeLog:

	* include/bits/version.def (initializer_list): Define with value
	202511 for C++26.
	* include/bits/version.h: Regenerate.
	* libsupc++/initializer_list (initializer_list::data)
	(initializer_list::empty) [__glibcxx_initializer_list >= 202511L]:
	Define.
	(std::begin(initializer_list<_Tp>), std::end(initializer_list<_Tp>)):
	Define only if __glibcxx_initializer_list < 202511L (i.e. not defined).
	* include/bits/range_access.h (std::empty(initializer_list<_Tp>))
	(std::data(initializer_list<_Tp>)): Define only if
	__glibcxx_initializer_list < 202511L (i.e. not defined).
	* testsuite/18_support/initializer_list/range_access.cc: Move test for
	brace-init list to range_access_neg.c. Included <iterator> in C++26 or
	later mode.
	* testsuite/18_support/initializer_list/data_empty_mem.cc: New test.
	* testsuite/18_support/initializer_list/range_access14.cc: New test.
	* testsuite/18_support/initializer_list/range_access14_neg.cc: New test.
	* testsuite/18_support/initializer_list/range_access17.cc: New test.
	* testsuite/18_support/initializer_list/range_access17_neg.cc: New test.
	* testsuite/18_support/initializer_list/range_access_neg.cc: New test.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>

diff --git a/libstdc++-v3/include/bits/range_access.h b/libstdc++-v3/include/bits/range_access.h
index 5a748257f1970dacae73e395b3e6a54a537dfc20..b89129f0233b7cc424984e8ab107850b377ddf2c 100644 (file)
--- a/libstdc++-v3/include/bits/range_access.h
+++ b/libstdc++-v3/include/bits/range_access.h
@@ -328,6 +328,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     empty(const _Tp (&)[_Nm]) noexcept
     { return false; }
 
+#if __glibcxx_initializer_list < 202511L
   /**
    *  @brief  Return whether an initializer_list is empty.
    *  @param  __il  Initializer list.
@@ -338,6 +339,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     constexpr bool
     empty(initializer_list<_Tp> __il) noexcept
     { return __il.size() == 0;}
+#endif
 
   /**
    *  @brief  Return the data pointer of a container.
@@ -374,6 +376,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     data(_Tp (&__array)[_Nm]) noexcept
     { return __array; }
 
+#if __glibcxx_initializer_list < 202511L
   /**
    *  @brief  Return the data pointer of an initializer list.
    *  @param  __il  Initializer list.
@@ -384,6 +387,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     constexpr const _Tp*
     data(initializer_list<_Tp> __il) noexcept
     { return __il.begin(); }
+#endif
 #endif // __glibcxx_nonmember_container_access
 
 #ifdef __glibcxx_ssize // C++ >= 20

diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index 1f0d3a2670e5c5b2d786ea30c39f91a31b41c492..14337b5b6b6d1010591493d868d5b090f6444394 100644 (file)
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -2410,6 +2410,14 @@ ftms = {
   };
 };
 
+ftms = {
+  name = initializer_list;
+  values = {
+    v = 202511;
+    cxxmin = 26;
+  };
+};
+
 // Standard test specifications.
 stds[97] = ">= 199711L";
 stds[03] = ">= 199711L";

diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index 66ac0ebef680033d0d699940ab03fce030d65d34..9402f25df375cb39066e3e43b5aa93e0d8f44521 100644 (file)
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -2675,4 +2675,14 @@
 #endif /* !defined(__cpp_lib_is_structural) */
 #undef __glibcxx_want_is_structural
 
+#if !defined(__cpp_lib_initializer_list)
+# if (__cplusplus >  202302L)
+#  define __glibcxx_initializer_list 202511L
+#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_initializer_list)
+#   define __cpp_lib_initializer_list 202511L
+#  endif
+# endif
+#endif /* !defined(__cpp_lib_initializer_list) */
+#undef __glibcxx_want_initializer_list
+
 #undef __glibcxx_want_all

diff --git a/libstdc++-v3/libsupc++/initializer_list b/libstdc++-v3/libsupc++/initializer_list
index baf47baa5f86da919a703bd5c436f0a6566a4fcc..fbea49dfb012af50a57a3f6b89703dab9d1839fa 100644 (file)
--- a/libstdc++-v3/libsupc++/initializer_list
+++ b/libstdc++-v3/libsupc++/initializer_list
@@ -40,6 +40,9 @@
 
 #include <bits/c++config.h>
 
+#define __glibcxx_want_initializer_list
+#include <bits/version.h>
+
 namespace std _GLIBCXX_VISIBILITY(default)
 {
   /// initializer_list
@@ -77,8 +80,17 @@ namespace std _GLIBCXX_VISIBILITY(default)
       // One past the last element.
       constexpr const_iterator
       end() const noexcept { return begin() + size(); }
+
+#if __glibcxx_initializer_list >= 202511L
+      constexpr bool
+      empty() const noexcept { return _M_len == 0; }
+
+      constexpr const value_type*
+      data() const noexcept { return _M_array; }
+#endif
     };
 
+#if __glibcxx_initializer_list < 202511L
   /**
    *  @brief  Return an iterator pointing to the first element of
    *          the initializer_list.
@@ -100,6 +112,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
     constexpr const _Tp*
     end(initializer_list<_Tp> __ils) noexcept
     { return __ils.end(); }
+#endif // __glibcxx_initializer_list < 202511L
 }
 
 #endif // C++11

diff --git a/libstdc++-v3/testsuite/18_support/initializer_list/data_empty_mem.cc b/libstdc++-v3/testsuite/18_support/initializer_list/data_empty_mem.cc
new file mode 100644 (file)
index 0000000..d5673eb
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/initializer_list/data_empty_mem.cc
@@ -0,0 +1,21 @@
+// { dg-do compile { target c++26 } }
+
+#include <initializer_list>
+#include <iterator>
+
+#ifndef __cpp_lib_initializer_list
+# error "Feature-test macro for text_encoding missing in <initializer_list>"
+#elif __cpp_lib_initializer_list != 202511L
+# error "Feature-test macro for text_encoding has wrong value in <initializer_list>"
+#endif
+
+void
+test02()
+{
+  static constexpr std::initializer_list<int> il{1};
+  static_assert( il.data() == il.begin() );
+  static_assert( il.empty() == false );
+  static_assert( noexcept(il.data()) );
+  static_assert( noexcept(il.empty()) );
+}
+

diff --git a/libstdc++-v3/testsuite/18_support/initializer_list/range_access.cc b/libstdc++-v3/testsuite/18_support/initializer_list/range_access.cc
index 8d7cb0dfb3f18410770b970ea60b7baa9b723685..feffd4ee4e435beca4e3250390c9d2bf01c0885a 100644 (file)
--- a/libstdc++-v3/testsuite/18_support/initializer_list/range_access.cc
+++ b/libstdc++-v3/testsuite/18_support/initializer_list/range_access.cc
@@ -20,16 +20,12 @@
 // 18.9.3 Initializer list range access [support.initlist.range]
 
 #include <initializer_list>
+#if __cpp_lib_initializer_list >= 202511L
+#  include <iterator>
+#endif
 
 void
 test01()
-{
-  std::begin({1, 2, 3});
-  std::end({1, 2, 3});
-}
-
-void
-test02()
 {
   static constexpr std::initializer_list<int> il{1};
   static_assert( std::begin(il) == il.begin() );

diff --git a/libstdc++-v3/testsuite/18_support/initializer_list/range_access14.cc b/libstdc++-v3/testsuite/18_support/initializer_list/range_access14.cc
new file mode 100644 (file)
index 0000000..b98e9cc
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/initializer_list/range_access14.cc
@@ -0,0 +1,24 @@
+// { dg-do compile { target c++14 } }
+
+#include <initializer_list>
+#include <iterator>
+
+void
+test01()
+{
+  static constexpr std::initializer_list<int> il{1, 2};
+  static_assert( std::cbegin(il) == il.begin() );
+  static_assert( std::cend(il) == il.end() );
+#if __cplusplus >= 201703L
+  static_assert( std::rbegin(il).base() == il.end() );
+  static_assert( std::rend(il).base() == il.begin() );
+  static_assert( std::rbegin(il).base() == il.end() );
+  static_assert( std::rend(il).base() == il.begin() );
+#endif 
+  static_assert( noexcept(std::cbegin(il)) );
+  static_assert( noexcept(std::cend(il)) );
+  static_assert( noexcept(std::rbegin(il)) );
+  static_assert( noexcept(std::rend(il)) );
+  static_assert( noexcept(std::crbegin(il)) );
+  static_assert( noexcept(std::crend(il)) );
+}

diff --git a/libstdc++-v3/testsuite/18_support/initializer_list/range_access14_neg.cc b/libstdc++-v3/testsuite/18_support/initializer_list/range_access14_neg.cc
new file mode 100644 (file)
index 0000000..e1c4062
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/initializer_list/range_access14_neg.cc
@@ -0,0 +1,18 @@
+// { dg-do compile { target c++17 } }
+
+#include <iterator>
+
+void
+test01()
+{
+  (void)std::cbegin({1, 2, 3});  // { dg-error "no matching function for call" }
+  (void)std::cend({1, 2, 3});    // { dg-error "no matching function for call" }
+  (void)std::rbegin({1, 2, 3});  // initializer_list overload not removed
+  (void)std::rend({1, 2, 3});    // initializer_list overload not removed
+  (void)std::crbegin({1, 2, 3}); // { dg-error "no matching function for call" }
+  (void)std::crend({1, 2, 3});   // { dg-error "no matching function for call" }
+
+}
+
+// { dg-prune-output "cannot bind non-const lvalue reference of type" }
+// { dg-prune-output "which is of non-class type" }

diff --git a/libstdc++-v3/testsuite/18_support/initializer_list/range_access17.cc b/libstdc++-v3/testsuite/18_support/initializer_list/range_access17.cc
new file mode 100644 (file)
index 0000000..443aae3
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/initializer_list/range_access17.cc
@@ -0,0 +1,16 @@
+// { dg-do compile { target c++17 } }
+
+#include <initializer_list>
+#include <iterator>
+
+void
+test01()
+{
+  static constexpr std::initializer_list<int> il{1};
+  static_assert( std::data(il) == il.begin() );
+  static_assert( std::size(il) == il.size() );
+  static_assert( !std::empty(il) );
+  static_assert( noexcept(std::data(il)) );
+  static_assert( noexcept(std::size(il)) );
+  static_assert( noexcept(std::empty(il)) );
+}

diff --git a/libstdc++-v3/testsuite/18_support/initializer_list/range_access17_neg.cc b/libstdc++-v3/testsuite/18_support/initializer_list/range_access17_neg.cc
new file mode 100644 (file)
index 0000000..fbe18f7
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/initializer_list/range_access17_neg.cc
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++17 } }
+
+#include <iterator>
+
+void
+test01()
+{
+  (void)std::data({1, 2, 3});  // { dg-error "no matching function for call" "" { target c++26 } }
+  (void)std::size({1, 2, 3});  // uses array overload
+  (void)std::empty({1, 2, 3}); // uses array overload
+}
+
+// { dg-prune-output "cannot bind non-const lvalue reference of type" }
+// { dg-prune-output "which is of non-class type" }

diff --git a/libstdc++-v3/testsuite/18_support/initializer_list/range_access_neg.cc b/libstdc++-v3/testsuite/18_support/initializer_list/range_access_neg.cc
new file mode 100644 (file)
index 0000000..e4bff4e
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/initializer_list/range_access_neg.cc
@@ -0,0 +1,13 @@
+// { dg-do compile { target c++11 } }
+
+#include <iterator>
+
+void
+test01()
+{
+  (void)std::begin({1, 2, 3}); // { dg-error "no matching function for call" "" { target c++26 } }
+  (void)std::end({1, 2, 3});   // { dg-error "no matching function for call" "" { target c++26 } }
+}
+
+// { dg-prune-output "cannot bind non-const lvalue reference of type" }
+// { dg-prune-output "which is of non-class type" }