# ===========================================================================

#  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' (for the C++11 standard)

#   or '14' (for the C++14 standard).

#

#   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 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 <bkoz@redhat.com>

#   Copyright (c) 2012 Zack Weinberg <zackw@panix.com>

#   Copyright (c) 2013 Roy Stogner <roystgnr@ices.utexas.edu>

#   Copyright (c) 2014, 2015 Google Inc.; contributed by Alexey Sokolov <sokolov@google.com>

#   Copyright (c) 2015 Paul Norman <penorman@mac.com>

#   Copyright (c) 2015 Moritz Klammler <moritz@klammler.eu>

#   Copyright (c) 2016, 2018 Krzesimir Nowak <qdlacz@gmail.com>

#   Copyright (c) 2019 Enji Cooper <yaneurabeya@gmail.com>

#

#   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 11

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"],

        [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], [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

)

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  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"

#elif __cplusplus < 201103L

#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

#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

#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;

    }