# ===========================================================================
#  https://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx.html
# ===========================================================================
#
# SYNOPSIS
#
#   AX_CXX_COMPILE_STDCXX(VERSION, [ext|noext], [mandatory|optional])
#
# DESCRIPTION
#
#   Check for baseline language coverage in the compiler for the specified
#   version of the C++ standard.  If necessary, add switches to CXX and
#   CXXCPP to enable support.  VERSION may be '11', '14', '17', or '20' for
#   the respective C++ standard version.
#
#   The second argument, if specified, indicates whether you insist on an
#   extended mode (e.g. -std=gnu++11) or a strict conformance mode (e.g.
#   -std=c++11).  If neither is specified, you get whatever works, with
#   preference for no added switch, and then for an extended mode.
#
#   The third argument, if specified 'mandatory' or if left unspecified,
#   indicates that baseline support for the specified C++ standard is
#   required and that the macro should error out if no mode with that
#   support is found.  If specified 'optional', then configuration proceeds
#   regardless, after defining HAVE_CXX${VERSION} if and only if a
#   supporting mode is found.
#
# LICENSE
#
#   Copyright (c) 2008 Benjamin Kosnik <[email protected]>
#   Copyright (c) 2012 Zack Weinberg <[email protected]>
#   Copyright (c) 2013 Roy Stogner <[email protected]>
#   Copyright (c) 2014, 2015 Google Inc.; contributed by Alexey Sokolov <[email protected]>
#   Copyright (c) 2015 Paul Norman <[email protected]>
#   Copyright (c) 2015 Moritz Klammler <[email protected]>
#   Copyright (c) 2016, 2018 Krzesimir Nowak <[email protected]>
#   Copyright (c) 2019 Enji Cooper <[email protected]>
#   Copyright (c) 2020 Jason Merrill <[email protected]>
#   Copyright (c) 2021 Jörn Heusipp <[email protected]>
#
#   Copying and distribution of this file, with or without modification, are
#   permitted in any medium without royalty provided the copyright notice
#   and this notice are preserved.  This file is offered as-is, without any
#   warranty.

#serial 15

dnl  This macro is based on the code from the AX_CXX_COMPILE_STDCXX_11 macro
dnl  (serial version number 13).

AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
 m4_if([$1], [11], [ax_cxx_compile_alternatives="11 0x"],
       [$1], [14], [ax_cxx_compile_alternatives="14 1y"],
       [$1], [17], [ax_cxx_compile_alternatives="17 1z"],
       [$1], [20], [ax_cxx_compile_alternatives="20"],
       [m4_fatal([invalid first argument `$1' to AX_CXX_COMPILE_STDCXX])])dnl
 m4_if([$2], [], [],
       [$2], [ext], [],
       [$2], [noext], [],
       [m4_fatal([invalid second argument `$2' to AX_CXX_COMPILE_STDCXX])])dnl
 m4_if([$3], [], [ax_cxx_compile_cxx$1_required=true],
       [$3], [mandatory], [ax_cxx_compile_cxx$1_required=true],
       [$3], [optional], [ax_cxx_compile_cxx$1_required=false],
       [m4_fatal([invalid third argument `$3' to AX_CXX_COMPILE_STDCXX])])
 AC_LANG_PUSH([C++])dnl
 ac_success=no

 m4_if([$2], [], [dnl
   AC_CACHE_CHECK(whether $CXX supports C++$1 features by default,
                  ax_cv_cxx_compile_cxx$1,
     [AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
       [ax_cv_cxx_compile_cxx$1=yes],
       [ax_cv_cxx_compile_cxx$1=no])])
   if test x$ax_cv_cxx_compile_cxx$1 = xyes; then
     ac_success=yes
   fi])

 m4_if([$2], [noext], [], [dnl
 if test x$ac_success = xno; then
   for alternative in ${ax_cxx_compile_alternatives}; do
     switch="-std=gnu++${alternative}"
     cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
     AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
                    $cachevar,
       [ac_save_CXX="$CXX"
        CXX="$CXX $switch"
        AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
         [eval $cachevar=yes],
         [eval $cachevar=no])
        CXX="$ac_save_CXX"])
     if eval test x\$$cachevar = xyes; then
       CXX="$CXX $switch"
       if test -n "$CXXCPP" ; then
         CXXCPP="$CXXCPP $switch"
       fi
       ac_success=yes
       break
     fi
   done
 fi])

 m4_if([$2], [ext], [], [dnl
 if test x$ac_success = xno; then
   dnl HP's aCC needs +std=c++11 according to:
   dnl http://h21007.www2.hp.com/portal/download/files/unprot/aCxx/PDF_Release_Notes/769149-001.pdf
   dnl Cray's crayCC needs "-h std=c++11"
   for alternative in ${ax_cxx_compile_alternatives}; do
     for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}"; do
       cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
       AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
                      $cachevar,
         [ac_save_CXX="$CXX"
          CXX="$CXX $switch"
          AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
           [eval $cachevar=yes],
           [eval $cachevar=no])
          CXX="$ac_save_CXX"])
       if eval test x\$$cachevar = xyes; then
         CXX="$CXX $switch"
         if test -n "$CXXCPP" ; then
           CXXCPP="$CXXCPP $switch"
         fi
         ac_success=yes
         break
       fi
     done
     if test x$ac_success = xyes; then
       break
     fi
   done
 fi])
 AC_LANG_POP([C++])
 if test x$ax_cxx_compile_cxx$1_required = xtrue; then
   if test x$ac_success = xno; then
     AC_MSG_ERROR([*** A compiler with support for C++$1 language features is required.])
   fi
 fi
 if test x$ac_success = xno; then
   HAVE_CXX$1=0
   AC_MSG_NOTICE([No compiler with C++$1 support was found])
 else
   HAVE_CXX$1=1
   AC_DEFINE(HAVE_CXX$1,1,
             [define if the compiler supports basic C++$1 syntax])
 fi
 AC_SUBST(HAVE_CXX$1)
])


dnl  Test body for checking C++11 support

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_11],
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
)

dnl  Test body for checking C++14 support

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_14],
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
)

dnl  Test body for checking C++17 support

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_17],
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
)

dnl  Test body for checking C++20 support

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_20],
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
 _AX_CXX_COMPILE_STDCXX_testbody_new_in_20
)


dnl  Tests for new features in C++11

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_11], [[

// If the compiler admits that it is not ready for C++11, why torture it?
// Hopefully, this will speed up the test.

#ifndef __cplusplus

#error "This is not a C++ compiler"

// MSVC always sets __cplusplus to 199711L in older versions; newer versions
// only set it correctly if /Zc:__cplusplus is specified as well as a
// /std:c++NN switch:
// https://devblogs.microsoft.com/cppblog/msvc-now-correctly-reports-__cplusplus/
#elif __cplusplus < 201103L && !defined _MSC_VER

#error "This is not a C++11 compiler"

#else

namespace cxx11
{

 namespace test_static_assert
 {

   template <typename T>
   struct check
   {
     static_assert(sizeof(int) <= sizeof(T), "not big enough");
   };

 }

 namespace test_final_override
 {

   struct Base
   {
     virtual ~Base() {}
     virtual void f() {}
   };

   struct Derived : public Base
   {
     virtual ~Derived() override {}
     virtual void f() override {}
   };

 }

 namespace test_double_right_angle_brackets
 {

   template < typename T >
   struct check {};

   typedef check<void> single_type;
   typedef check<check<void>> double_type;
   typedef check<check<check<void>>> triple_type;
   typedef check<check<check<check<void>>>> quadruple_type;

 }

 namespace test_decltype
 {

   int
   f()
   {
     int a = 1;
     decltype(a) b = 2;
     return a + b;
   }

 }

 namespace test_type_deduction
 {

   template < typename T1, typename T2 >
   struct is_same
   {
     static const bool value = false;
   };

   template < typename T >
   struct is_same<T, T>
   {
     static const bool value = true;
   };

   template < typename T1, typename T2 >
   auto
   add(T1 a1, T2 a2) -> decltype(a1 + a2)
   {
     return a1 + a2;
   }

   int
   test(const int c, volatile int v)
   {
     static_assert(is_same<int, decltype(0)>::value == true, "");
     static_assert(is_same<int, decltype(c)>::value == false, "");
     static_assert(is_same<int, decltype(v)>::value == false, "");
     auto ac = c;
     auto av = v;
     auto sumi = ac + av + 'x';
     auto sumf = ac + av + 1.0;
     static_assert(is_same<int, decltype(ac)>::value == true, "");
     static_assert(is_same<int, decltype(av)>::value == true, "");
     static_assert(is_same<int, decltype(sumi)>::value == true, "");
     static_assert(is_same<int, decltype(sumf)>::value == false, "");
     static_assert(is_same<int, decltype(add(c, v))>::value == true, "");
     return (sumf > 0.0) ? sumi : add(c, v);
   }

 }

 namespace test_noexcept
 {

   int f() { return 0; }
   int g() noexcept { return 0; }

   static_assert(noexcept(f()) == false, "");
   static_assert(noexcept(g()) == true, "");

 }

 namespace test_constexpr
 {

   template < typename CharT >
   unsigned long constexpr
   strlen_c_r(const CharT *const s, const unsigned long acc) noexcept
   {
     return *s ? strlen_c_r(s + 1, acc + 1) : acc;
   }

   template < typename CharT >
   unsigned long constexpr
   strlen_c(const CharT *const s) noexcept
   {
     return strlen_c_r(s, 0UL);
   }

   static_assert(strlen_c("") == 0UL, "");
   static_assert(strlen_c("1") == 1UL, "");
   static_assert(strlen_c("example") == 7UL, "");
   static_assert(strlen_c("another\0example") == 7UL, "");

 }

 namespace test_rvalue_references
 {

   template < int N >
   struct answer
   {
     static constexpr int value = N;
   };

   answer<1> f(int&)       { return answer<1>(); }
   answer<2> f(const int&) { return answer<2>(); }
   answer<3> f(int&&)      { return answer<3>(); }

   void
   test()
   {
     int i = 0;
     const int c = 0;
     static_assert(decltype(f(i))::value == 1, "");
     static_assert(decltype(f(c))::value == 2, "");
     static_assert(decltype(f(0))::value == 3, "");
   }

 }

 namespace test_uniform_initialization
 {

   struct test
   {
     static const int zero {};
     static const int one {1};
   };

   static_assert(test::zero == 0, "");
   static_assert(test::one == 1, "");

 }

 namespace test_lambdas
 {

   void
   test1()
   {
     auto lambda1 = [](){};
     auto lambda2 = lambda1;
     lambda1();
     lambda2();
   }

   int
   test2()
   {
     auto a = [](int i, int j){ return i + j; }(1, 2);
     auto b = []() -> int { return '0'; }();
     auto c = [=](){ return a + b; }();
     auto d = [&](){ return c; }();
     auto e = [a, &b](int x) mutable {
       const auto identity = [](int y){ return y; };
       for (auto i = 0; i < a; ++i)
         a += b--;
       return x + identity(a + b);
     }(0);
     return a + b + c + d + e;
   }

   int
   test3()
   {
     const auto nullary = [](){ return 0; };
     const auto unary = [](int x){ return x; };
     using nullary_t = decltype(nullary);
     using unary_t = decltype(unary);
     const auto higher1st = [](nullary_t f){ return f(); };
     const auto higher2nd = [unary](nullary_t f1){
       return [unary, f1](unary_t f2){ return f2(unary(f1())); };
     };
     return higher1st(nullary) + higher2nd(nullary)(unary);
   }

 }

 namespace test_variadic_templates
 {

   template <int...>
   struct sum;

   template <int N0, int... N1toN>
   struct sum<N0, N1toN...>
   {
     static constexpr auto value = N0 + sum<N1toN...>::value;
   };

   template <>
   struct sum<>
   {
     static constexpr auto value = 0;
   };

   static_assert(sum<>::value == 0, "");
   static_assert(sum<1>::value == 1, "");
   static_assert(sum<23>::value == 23, "");
   static_assert(sum<1, 2>::value == 3, "");
   static_assert(sum<5, 5, 11>::value == 21, "");
   static_assert(sum<2, 3, 5, 7, 11, 13>::value == 41, "");

 }

 // http://stackoverflow.com/questions/13728184/template-aliases-and-sfinae
 // Clang 3.1 fails with headers of libstd++ 4.8.3 when using std::function
 // because of this.
 namespace test_template_alias_sfinae
 {

   struct foo {};

   template<typename T>
   using member = typename T::member_type;

   template<typename T>
   void func(...) {}

   template<typename T>
   void func(member<T>*) {}

   void test();

   void test() { func<foo>(0); }

 }

}  // namespace cxx11

#endif  // __cplusplus >= 201103L

]])


dnl  Tests for new features in C++14

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_14], [[

// If the compiler admits that it is not ready for C++14, why torture it?
// Hopefully, this will speed up the test.

#ifndef __cplusplus

#error "This is not a C++ compiler"

#elif __cplusplus < 201402L && !defined _MSC_VER

#error "This is not a C++14 compiler"

#else

namespace cxx14
{

 namespace test_polymorphic_lambdas
 {

   int
   test()
   {
     const auto lambda = [](auto&&... args){
       const auto istiny = [](auto x){
         return (sizeof(x) == 1UL) ? 1 : 0;
       };
       const int aretiny[] = { istiny(args)... };
       return aretiny[0];
     };
     return lambda(1, 1L, 1.0f, '1');
   }

 }

 namespace test_binary_literals
 {

   constexpr auto ivii = 0b0000000000101010;
   static_assert(ivii == 42, "wrong value");

 }

 namespace test_generalized_constexpr
 {

   template < typename CharT >
   constexpr unsigned long
   strlen_c(const CharT *const s) noexcept
   {
     auto length = 0UL;
     for (auto p = s; *p; ++p)
       ++length;
     return length;
   }

   static_assert(strlen_c("") == 0UL, "");
   static_assert(strlen_c("x") == 1UL, "");
   static_assert(strlen_c("test") == 4UL, "");
   static_assert(strlen_c("another\0test") == 7UL, "");

 }

 namespace test_lambda_init_capture
 {

   int
   test()
   {
     auto x = 0;
     const auto lambda1 = [a = x](int b){ return a + b; };
     const auto lambda2 = [a = lambda1(x)](){ return a; };
     return lambda2();
   }

 }

 namespace test_digit_separators
 {

   constexpr auto ten_million = 100'000'000;
   static_assert(ten_million == 100000000, "");

 }

 namespace test_return_type_deduction
 {

   auto f(int& x) { return x; }
   decltype(auto) g(int& x) { return x; }

   template < typename T1, typename T2 >
   struct is_same
   {
     static constexpr auto value = false;
   };

   template < typename T >
   struct is_same<T, T>
   {
     static constexpr auto value = true;
   };

   int
   test()
   {
     auto x = 0;
     static_assert(is_same<int, decltype(f(x))>::value, "");
     static_assert(is_same<int&, decltype(g(x))>::value, "");
     return x;
   }

 }

}  // namespace cxx14

#endif  // __cplusplus >= 201402L

]])


dnl  Tests for new features in C++17

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_17], [[

// If the compiler admits that it is not ready for C++17, why torture it?
// Hopefully, this will speed up the test.

#ifndef __cplusplus

#error "This is not a C++ compiler"

#elif __cplusplus < 201703L && !defined _MSC_VER

#error "This is not a C++17 compiler"

#else

#include <initializer_list>
#include <utility>
#include <type_traits>

namespace cxx17
{

 namespace test_constexpr_lambdas
 {

   constexpr int foo = [](){return 42;}();

 }

 namespace test::nested_namespace::definitions
 {

 }

 namespace test_fold_expression
 {

   template<typename... Args>
   int multiply(Args... args)
   {
     return (args * ... * 1);
   }

   template<typename... Args>
   bool all(Args... args)
   {
     return (args && ...);
   }

 }

 namespace test_extended_static_assert
 {

   static_assert (true);

 }

 namespace test_auto_brace_init_list
 {

   auto foo = {5};
   auto bar {5};

   static_assert(std::is_same<std::initializer_list<int>, decltype(foo)>::value);
   static_assert(std::is_same<int, decltype(bar)>::value);
 }

 namespace test_typename_in_template_template_parameter
 {

   template<template<typename> typename X> struct D;

 }

 namespace test_fallthrough_nodiscard_maybe_unused_attributes
 {

   int f1()
   {
     return 42;
   }

   [[nodiscard]] int f2()
   {
     [[maybe_unused]] auto unused = f1();

     switch (f1())
     {
     case 17:
       f1();
       [[fallthrough]];
     case 42:
       f1();
     }
     return f1();
   }

 }

 namespace test_extended_aggregate_initialization
 {

   struct base1
   {
     int b1, b2 = 42;
   };

   struct base2
   {
     base2() {
       b3 = 42;
     }
     int b3;
   };

   struct derived : base1, base2
   {
       int d;
   };

   derived d1 {{1, 2}, {}, 4};  // full initialization
   derived d2 {{}, {}, 4};      // value-initialized bases

 }

 namespace test_general_range_based_for_loop
 {

   struct iter
   {
     int i;

     int& operator* ()
     {
       return i;
     }

     const int& operator* () const
     {
       return i;
     }

     iter& operator++()
     {
       ++i;
       return *this;
     }
   };

   struct sentinel
   {
     int i;
   };

   bool operator== (const iter& i, const sentinel& s)
   {
     return i.i == s.i;
   }

   bool operator!= (const iter& i, const sentinel& s)
   {
     return !(i == s);
   }

   struct range
   {
     iter begin() const
     {
       return {0};
     }

     sentinel end() const
     {
       return {5};
     }
   };

   void f()
   {
     range r {};

     for (auto i : r)
     {
       [[maybe_unused]] auto v = i;
     }
   }

 }

 namespace test_lambda_capture_asterisk_this_by_value
 {

   struct t
   {
     int i;
     int foo()
     {
       return [*this]()
       {
         return i;
       }();
     }
   };

 }

 namespace test_enum_class_construction
 {

   enum class byte : unsigned char
   {};

   byte foo {42};

 }

 namespace test_constexpr_if
 {

   template <bool cond>
   int f ()
   {
     if constexpr(cond)
     {
       return 13;
     }
     else
     {
       return 42;
     }
   }

 }

 namespace test_selection_statement_with_initializer
 {

   int f()
   {
     return 13;
   }

   int f2()
   {
     if (auto i = f(); i > 0)
     {
       return 3;
     }

     switch (auto i = f(); i + 4)
     {
     case 17:
       return 2;

     default:
       return 1;
     }
   }

 }

 namespace test_template_argument_deduction_for_class_templates
 {

   template <typename T1, typename T2>
   struct pair
   {
     pair (T1 p1, T2 p2)
       : m1 {p1},
         m2 {p2}
     {}

     T1 m1;
     T2 m2;
   };

   void f()
   {
     [[maybe_unused]] auto p = pair{13, 42u};
   }

 }

 namespace test_non_type_auto_template_parameters
 {

   template <auto n>
   struct B
   {};

   B<5> b1;
   B<'a'> b2;

 }

 namespace test_structured_bindings
 {

   int arr[2] = { 1, 2 };
   std::pair<int, int> pr = { 1, 2 };

   auto f1() -> int(&)[2]
   {
     return arr;
   }

   auto f2() -> std::pair<int, int>&
   {
     return pr;
   }

   struct S
   {
     int x1 : 2;
     volatile double y1;
   };

   S f3()
   {
     return {};
   }

   auto [ x1, y1 ] = f1();
   auto& [ xr1, yr1 ] = f1();
   auto [ x2, y2 ] = f2();
   auto& [ xr2, yr2 ] = f2();
   const auto [ x3, y3 ] = f3();

 }

 namespace test_exception_spec_type_system
 {

   struct Good {};
   struct Bad {};

   void g1() noexcept;
   void g2();

   template<typename T>
   Bad
   f(T*, T*);

   template<typename T1, typename T2>
   Good
   f(T1*, T2*);

   static_assert (std::is_same_v<Good, decltype(f(g1, g2))>);

 }

 namespace test_inline_variables
 {

   template<class T> void f(T)
   {}

   template<class T> inline T g(T)
   {
     return T{};
   }

   template<> inline void f<>(int)
   {}

   template<> int g<>(int)
   {
     return 5;
   }

 }

}  // namespace cxx17

#endif  // __cplusplus < 201703L && !defined _MSC_VER

]])


dnl  Tests for new features in C++20

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_20], [[

#ifndef __cplusplus

#error "This is not a C++ compiler"

#elif __cplusplus < 202002L && !defined _MSC_VER

#error "This is not a C++20 compiler"

#else

#include <version>

namespace cxx20
{

// As C++20 supports feature test macros in the standard, there is no
// immediate need to actually test for feature availability on the
// Autoconf side.

}  // namespace cxx20

#endif  // __cplusplus < 202002L && !defined _MSC_VER

]])

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