[libc++] Make charconv require C++17 or later.

Implementing the paper
P2291R3 Add Constexpr Modifiers to Functions to_chars and from_chars for
        Integral Types in <charconv> Header

Gives issues in language versions prior to C++17. As suggested in
D131855 disable the code prior to C++17. This removes libc++'s
extension.

Reviewed By: ldionne, #libc_vendors, #libc, philnik

Differential Revision: https://reviews.llvm.org/D133216

13 files changed, 26 insertions, 36 deletions

diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
index 8a49ec4..b010213e 100644
--- a/libcxx/docs/ReleaseNotes.rst
+++ b/libcxx/docs/ReleaseNotes.rst
@@ -78,6 +78,12 @@ Deprecations and Removals
   reach out to the libc++ developers if you find something missing in the new
   configuration system.
 
+- The functions ``to_chars`` and ``from_chars`` for integral types are
+  available starting with C++17. Libc++ offered these functions in C++11 and
+  C++14 as an undocumented extension. This extension makes it hard to implement
+  the C++23 paper that makes these functions ``constexpr``, therefore the
+  extension has been removed.
+
 Upcoming Deprecations and Removals
 ----------------------------------
 
diff --git a/libcxx/include/__charconv/chars_format.h b/libcxx/include/__charconv/chars_format.h
index 8028e2e..695bd87 100644
--- a/libcxx/include/__charconv/chars_format.h
+++ b/libcxx/include/__charconv/chars_format.h
@@ -19,7 +19,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifndef _LIBCPP_CXX03_LANG
+#if _LIBCPP_STD_VER > 14
 
 enum class _LIBCPP_ENUM_VIS chars_format
 {
@@ -70,7 +70,7 @@ operator^=(chars_format& __x, chars_format __y) {
   return __x;
 }
 
-#endif // _LIBCPP_CXX03_LANG
+#endif // _LIBCPP_STD_VER > 14
 
 _LIBCPP_END_NAMESPACE_STD
 
diff --git a/libcxx/include/__charconv/from_chars_result.h b/libcxx/include/__charconv/from_chars_result.h
index 2cc3c11..05ffe148 100644
--- a/libcxx/include/__charconv/from_chars_result.h
+++ b/libcxx/include/__charconv/from_chars_result.h
@@ -19,7 +19,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifndef _LIBCPP_CXX03_LANG
+#if _LIBCPP_STD_VER > 14
 
 struct _LIBCPP_TYPE_VIS from_chars_result
 {
@@ -30,7 +30,7 @@ struct _LIBCPP_TYPE_VIS from_chars_result
 #  endif
 };
 
-#endif // _LIBCPP_CXX03_LANG
+#endif // _LIBCPP_STD_VER > 14
 
 _LIBCPP_END_NAMESPACE_STD
 
diff --git a/libcxx/include/__charconv/tables.h b/libcxx/include/__charconv/tables.h
index 83f39e6..08664d7 100644
--- a/libcxx/include/__charconv/tables.h
+++ b/libcxx/include/__charconv/tables.h
@@ -19,7 +19,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifndef _LIBCPP_CXX03_LANG
+#if _LIBCPP_STD_VER > 14
 
 namespace __itoa {
 
@@ -173,7 +173,7 @@ const char __table<_Tp>::__digits_base_10[200] = {
 
 } // namespace __itoa
 
-#endif // _LIBCPP_CXX03_LANG
+#endif // _LIBCPP_STD_VER > 14
 
 _LIBCPP_END_NAMESPACE_STD
 
diff --git a/libcxx/include/__charconv/to_chars_base_10.h b/libcxx/include/__charconv/to_chars_base_10.h
index d25deff..0c47597 100644
--- a/libcxx/include/__charconv/to_chars_base_10.h
+++ b/libcxx/include/__charconv/to_chars_base_10.h
@@ -25,7 +25,7 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifndef _LIBCPP_CXX03_LANG
+#if _LIBCPP_STD_VER > 14
 
 namespace __itoa {
 
@@ -176,7 +176,7 @@ _LIBCPP_HIDE_FROM_ABI inline char* __base_10_u128(char* __buffer, __uint128_t __
 #  endif
 } // namespace __itoa
 
-#endif // _LIBCPP_CXX03_LANG
+#endif // _LIBCPP_STD_VER > 14
 
 _LIBCPP_END_NAMESPACE_STD
 
diff --git a/libcxx/include/__charconv/to_chars_result.h b/libcxx/include/__charconv/to_chars_result.h
index b4bc6ac..2eb4098 100644
--- a/libcxx/include/__charconv/to_chars_result.h
+++ b/libcxx/include/__charconv/to_chars_result.h
@@ -19,7 +19,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifndef _LIBCPP_CXX03_LANG
+#if _LIBCPP_STD_VER > 14
 
 struct _LIBCPP_TYPE_VIS to_chars_result
 {
@@ -30,7 +30,7 @@ struct _LIBCPP_TYPE_VIS to_chars_result
 #  endif
 };
 
-#endif // _LIBCPP_CXX03_LANG
+#endif // _LIBCPP_STD_VER > 14
 
 _LIBCPP_END_NAMESPACE_STD
 
diff --git a/libcxx/include/charconv b/libcxx/include/charconv
index 35ac05e..8e58d96 100644
--- a/libcxx/include/charconv
+++ b/libcxx/include/charconv
@@ -106,7 +106,7 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifndef _LIBCPP_CXX03_LANG
+#if _LIBCPP_STD_VER > 14
 
 to_chars_result to_chars(char*, char*, bool, int = 10) = delete;
 from_chars_result from_chars(const char*, const char*, bool, int = 10) = delete;
@@ -776,10 +776,6 @@ from_chars(const char* __first, const char* __last, _Tp& __value, int __base)
     return __from_chars_integral(__first, __last, __value, __base);
 }
 
-// Floating-point implementation starts here.
-// Unlike the other parts of charconv this is only available in C++17 and newer.
-#if _LIBCPP_STD_VER > 14
-
 _LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
 to_chars_result to_chars(char* __first, char* __last, float __value);
 
@@ -807,8 +803,7 @@ to_chars_result to_chars(char* __first, char* __last, double __value, chars_form
 _LIBCPP_AVAILABILITY_TO_CHARS_FLOATING_POINT _LIBCPP_FUNC_VIS
 to_chars_result to_chars(char* __first, char* __last, long double __value, chars_format __fmt, int __precision);
 
-#  endif // _LIBCPP_STD_VER > 14
-#endif // _LIBCPP_CXX03_LANG
+#endif // _LIBCPP_STD_VER > 14
 
 _LIBCPP_END_NAMESPACE_STD
 
diff --git a/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.bool.fail.cpp b/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.bool.fail.cpp
index d771317..5fa62a46 100644
--- a/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.bool.fail.cpp
+++ b/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.bool.fail.cpp
@@ -6,9 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03
-// UNSUPPORTED: !stdlib=libc++ && c++11
-// UNSUPPORTED: !stdlib=libc++ && c++14
+// UNSUPPORTED: c++03, c++11, c++14
+
 // <charconv>
 
 // In
diff --git a/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.pass.cpp b/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.pass.cpp
index fd47cb4..9cd006d 100644
--- a/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.pass.cpp
+++ b/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.pass.cpp
@@ -6,9 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03
-// UNSUPPORTED: !stdlib=libc++ && c++11
-// UNSUPPORTED: !stdlib=libc++ && c++14
+// UNSUPPORTED: c++03, c++11, c++14
 
 // <charconv>
 
diff --git a/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.roundtrip.pass.cpp b/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.roundtrip.pass.cpp
index cd90fae..70cefa4 100644
--- a/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.roundtrip.pass.cpp
+++ b/libcxx/test/std/utilities/charconv/charconv.from.chars/integral.roundtrip.pass.cpp
@@ -6,9 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03
-// UNSUPPORTED: !stdlib=libc++ && c++11
-// UNSUPPORTED: !stdlib=libc++ && c++14
+// UNSUPPORTED: c++03, c++11, c++14
 
 // <charconv>
 
diff --git a/libcxx/test/std/utilities/charconv/charconv.syn/chars_format.pass.cpp b/libcxx/test/std/utilities/charconv/charconv.syn/chars_format.pass.cpp
index 475852f..beee526 100644
--- a/libcxx/test/std/utilities/charconv/charconv.syn/chars_format.pass.cpp
+++ b/libcxx/test/std/utilities/charconv/charconv.syn/chars_format.pass.cpp
@@ -6,10 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Note: chars_format is a C++17 feature backported to C++11. Assert isn't
-// allowed in a constexpr function in C++11. To keep the code readable, C++11
-// support is untested.
-// UNSUPPORTED: c++03, c++11
+// UNSUPPORTED: c++03, c++11, c++14
 
 // <charconv>
 
diff --git a/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.bool.fail.cpp b/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.bool.fail.cpp
index 096d979..630799b 100644
--- a/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.bool.fail.cpp
+++ b/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.bool.fail.cpp
@@ -6,9 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03
-// UNSUPPORTED: !stdlib=libc++ && c++11
-// UNSUPPORTED: !stdlib=libc++ && c++14
+// UNSUPPORTED: c++03, c++11, c++14
+
 // <charconv>
 
 // In
diff --git a/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.pass.cpp b/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.pass.cpp
index 1b83307..fa6c214 100644
--- a/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.pass.cpp
+++ b/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.pass.cpp
@@ -6,9 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: c++03
-// UNSUPPORTED: !stdlib=libc++ && c++11
-// UNSUPPORTED: !stdlib=libc++ && c++14
+// UNSUPPORTED: c++03, c++11, c++14
 
 // ADDITIONAL_COMPILE_FLAGS(has-fconstexpr-steps): -fconstexpr-steps=12712420
 // ADDITIONAL_COMPILE_FLAGS(has-fconstexpr-ops-limit): -fconstexpr-ops-limit=12712420