gdb/ax_cxx_compile_stdcxx.m4

   1 # Copyright (c) 2016-2020 Free Software Foundation, Inc.
   2 #
   3 # Originally based on the AX_CXX_COMPILE_STDCXX macro found at the url
   4 # below.
   5 #
   6 # Local GDB customizations:
   7 #
   8 # - AC_SUBST CXX_DIALECT instead of changing CXX/CXXCPP.
   9 #
  10 # ===========================================================================
  11 #  https://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx.html
  12 # ===========================================================================
  13 #
  14 # SYNOPSIS
  15 #
  16 #   AX_CXX_COMPILE_STDCXX(VERSION, [ext|noext], [mandatory|optional])
  17 #
  18 # DESCRIPTION
  19 #
  20 #   Check for baseline language coverage in the compiler for the specified
  21 #   version of the C++ standard.  If necessary, add switches to CXX and
  22 #   CXXCPP to enable support.  VERSION may be '11' (for the C++11 standard)
  23 #   or '14' (for the C++14 standard).
  24 #
  25 #   The second argument, if specified, indicates whether you insist on an
  26 #   extended mode (e.g. -std=gnu++11) or a strict conformance mode (e.g.
  27 #   -std=c++11).  If neither is specified, you get whatever works, with
  28 #   preference for an extended mode.
  29 #
  30 #   The third argument, if specified 'mandatory' or if left unspecified,
  31 #   indicates that baseline support for the specified C++ standard is
  32 #   required and that the macro should error out if no mode with that
  33 #   support is found.  If specified 'optional', then configuration proceeds
  34 #   regardless, after defining HAVE_CXX${VERSION} if and only if a
  35 #   supporting mode is found.
  36 #
  37 # LICENSE
  38 #
  39 #   Copyright (c) 2008 Benjamin Kosnik <bkoz@redhat.com>
  40 #   Copyright (c) 2012 Zack Weinberg <zackw@panix.com>
  41 #   Copyright (c) 2013 Roy Stogner <roystgnr@ices.utexas.edu>
  42 #   Copyright (c) 2014, 2015 Google Inc.; contributed by Alexey Sokolov <sokolov@google.com>
  43 #   Copyright (c) 2015 Paul Norman <penorman@mac.com>
  44 #   Copyright (c) 2015 Moritz Klammler <moritz@klammler.eu>
  45 #   Copyright (c) 2016 Krzesimir Nowak <qdlacz@gmail.com>
  46 #
  47 #   Copying and distribution of this file, with or without modification, are
  48 #   permitted in any medium without royalty provided the copyright notice
  49 #   and this notice are preserved.  This file is offered as-is, without any
  50 #   warranty.
  51
  52 #serial 8
  53
  54 dnl  This macro is based on the code from the AX_CXX_COMPILE_STDCXX_11 macro
  55 dnl  (serial version number 13).
  56
  57 AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
  58   m4_if([$1], [11], [ax_cxx_compile_alternatives="11 0x"],
  59         [$1], [14], [ax_cxx_compile_alternatives="14 1y"],
  60         [$1], [17], [ax_cxx_compile_alternatives="17 1z"],
  61         [m4_fatal([invalid first argument `$1' to AX_CXX_COMPILE_STDCXX])])dnl
  62   m4_if([$2], [], [],
  63         [$2], [ext], [],
  64         [$2], [noext], [],
  65         [m4_fatal([invalid second argument `$2' to AX_CXX_COMPILE_STDCXX])])dnl
  66   m4_if([$3], [], [ax_cxx_compile_cxx$1_required=true],
  67         [$3], [mandatory], [ax_cxx_compile_cxx$1_required=true],
  68         [$3], [optional], [ax_cxx_compile_cxx$1_required=false],
  69         [m4_fatal([invalid third argument `$3' to AX_CXX_COMPILE_STDCXX])])
  70   AC_LANG_PUSH([C++])dnl
  71   CXX_DIALECT=""
  72   ac_success=no
  73   AC_CACHE_CHECK(whether $CXX supports C++$1 features by default,
  74   ax_cv_cxx_compile_cxx$1,
  75   [AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
  76     [ax_cv_cxx_compile_cxx$1=yes],
  77     [ax_cv_cxx_compile_cxx$1=no])])
  78   if test x$ax_cv_cxx_compile_cxx$1 = xyes; then
  79     ac_success=yes
  80   fi
  81
  82   m4_if([$2], [noext], [], [dnl
  83   if test x$ac_success = xno; then
  84     for alternative in ${ax_cxx_compile_alternatives}; do
  85       switch="-std=gnu++${alternative}"
  86       cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
  87       AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
  88                      $cachevar,
  89         [ac_save_CXX="$CXX"
  90          CXX="$CXX $switch"
  91          AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
  92           [eval $cachevar=yes],
  93           [eval $cachevar=no])
  94          CXX="$ac_save_CXX"])
  95       if eval test x\$$cachevar = xyes; then
  96         CXX_DIALECT="$switch"
  97         ac_success=yes
  98         break
  99       fi
 100     done
 101   fi])
 102
 103   m4_if([$2], [ext], [], [dnl
 104   if test x$ac_success = xno; then
 105     dnl HP's aCC needs +std=c++11 according to:
 106     dnl http://h21007.www2.hp.com/portal/download/files/unprot/aCxx/PDF_Release_Notes/769149-001.pdf
 107     dnl Cray's crayCC needs "-h std=c++11"
 108     for alternative in ${ax_cxx_compile_alternatives}; do
 109       for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}"; do
 110         cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
 111         AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
 112                        $cachevar,
 113           [ac_save_CXX="$CXX"
 114            CXX="$CXX $switch"
 115            AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
 116             [eval $cachevar=yes],
 117             [eval $cachevar=no])
 118            CXX="$ac_save_CXX"])
 119         if eval test x\$$cachevar = xyes; then
 120           CXX_DIALECT="$switch"
 121           ac_success=yes
 122           break
 123         fi
 124       done
 125       if test x$ac_success = xyes; then
 126         break
 127       fi
 128     done
 129   fi])
 130   AC_LANG_POP([C++])
 131   if test x$ax_cxx_compile_cxx$1_required = xtrue; then
 132     if test x$ac_success = xno; then
 133       AC_MSG_ERROR([*** A compiler with support for C++$1 language features is required.])
 134     fi
 135   fi
 136   if test x$ac_success = xno; then
 137     HAVE_CXX$1=0
 138     AC_MSG_NOTICE([No compiler with C++$1 support was found])
 139   else
 140     HAVE_CXX$1=1
 141     AC_DEFINE(HAVE_CXX$1,1,
 142               [define if the compiler supports basic C++$1 syntax])
 143   fi
 144   AC_SUBST(HAVE_CXX$1)
 145   AC_SUBST(CXX_DIALECT)
 146 ])
 147
 148
 149 dnl  Test body for checking C++11 support
 150
 151 m4_define([_AX_CXX_COMPILE_STDCXX_testbody_11],
 152   _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
 153 )
 154
 155
 156 dnl  Test body for checking C++14 support
 157
 158 m4_define([_AX_CXX_COMPILE_STDCXX_testbody_14],
 159   _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
 160   _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
 161 )
 162
 163 m4_define([_AX_CXX_COMPILE_STDCXX_testbody_17],
 164   _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
 165   _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
 166   _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
 167 )
 168
 169 dnl  Tests for new features in C++11
 170
 171 m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_11], [[
 172
 173 // If the compiler admits that it is not ready for C++11, why torture it?
 174 // Hopefully, this will speed up the test.
 175
 176 #ifndef __cplusplus
 177
 178 #error "This is not a C++ compiler"
 179
 180 #elif __cplusplus < 201103L
 181
 182 #error "This is not a C++11 compiler"
 183
 184 #else
 185
 186 namespace cxx11
 187 {
 188
 189   namespace test_static_assert
 190   {
 191
 192     template <typename T>
 193     struct check
 194     {
 195       static_assert(sizeof(int) <= sizeof(T), "not big enough");
 196     };
 197
 198   }
 199
 200   namespace test_final_override
 201   {
 202
 203     struct Base
 204     {
 205       virtual void f() {}
 206     };
 207
 208     struct Derived : public Base
 209     {
 210       virtual void f() override {}
 211     };
 212
 213   }
 214
 215   namespace test_double_right_angle_brackets
 216   {
 217
 218     template < typename T >
 219     struct check {};
 220
 221     typedef check<void> single_type;
 222     typedef check<check<void>> double_type;
 223     typedef check<check<check<void>>> triple_type;
 224     typedef check<check<check<check<void>>>> quadruple_type;
 225
 226   }
 227
 228   namespace test_decltype
 229   {
 230
 231     int
 232     f()
 233     {
 234       int a = 1;
 235       decltype(a) b = 2;
 236       return a + b;
 237     }
 238
 239   }
 240
 241   namespace test_type_deduction
 242   {
 243
 244     template < typename T1, typename T2 >
 245     struct is_same
 246     {
 247       static const bool value = false;
 248     };
 249
 250     template < typename T >
 251     struct is_same<T, T>
 252     {
 253       static const bool value = true;
 254     };
 255
 256     template < typename T1, typename T2 >
 257     auto
 258     add(T1 a1, T2 a2) -> decltype(a1 + a2)
 259     {
 260       return a1 + a2;
 261     }
 262
 263     int
 264     test(const int c, volatile int v)
 265     {
 266       static_assert(is_same<int, decltype(0)>::value == true, "");
 267       static_assert(is_same<int, decltype(c)>::value == false, "");
 268       static_assert(is_same<int, decltype(v)>::value == false, "");
 269       auto ac = c;
 270       auto av = v;
 271       auto sumi = ac + av + 'x';
 272       auto sumf = ac + av + 1.0;
 273       static_assert(is_same<int, decltype(ac)>::value == true, "");
 274       static_assert(is_same<int, decltype(av)>::value == true, "");
 275       static_assert(is_same<int, decltype(sumi)>::value == true, "");
 276       static_assert(is_same<int, decltype(sumf)>::value == false, "");
 277       static_assert(is_same<int, decltype(add(c, v))>::value == true, "");
 278       return (sumf > 0.0) ? sumi : add(c, v);
 279     }
 280
 281   }
 282
 283   namespace test_noexcept
 284   {
 285
 286     int f() { return 0; }
 287     int g() noexcept { return 0; }
 288
 289     static_assert(noexcept(f()) == false, "");
 290     static_assert(noexcept(g()) == true, "");
 291
 292   }
 293
 294   namespace test_constexpr
 295   {
 296
 297     template < typename CharT >
 298     unsigned long constexpr
 299     strlen_c_r(const CharT *const s, const unsigned long acc) noexcept
 300     {
 301       return *s ? strlen_c_r(s + 1, acc + 1) : acc;
 302     }
 303
 304     template < typename CharT >
 305     unsigned long constexpr
 306     strlen_c(const CharT *const s) noexcept
 307     {
 308       return strlen_c_r(s, 0UL);
 309     }
 310
 311     static_assert(strlen_c("") == 0UL, "");
 312     static_assert(strlen_c("1") == 1UL, "");
 313     static_assert(strlen_c("example") == 7UL, "");
 314     static_assert(strlen_c("another\0example") == 7UL, "");
 315
 316   }
 317
 318   namespace test_rvalue_references
 319   {
 320
 321     template < int N >
 322     struct answer
 323     {
 324       static constexpr int value = N;
 325     };
 326
 327     answer<1> f(int&)       { return answer<1>(); }
 328     answer<2> f(const int&) { return answer<2>(); }
 329     answer<3> f(int&&)      { return answer<3>(); }
 330
 331     void
 332     test()
 333     {
 334       int i = 0;
 335       const int c = 0;
 336       static_assert(decltype(f(i))::value == 1, "");
 337       static_assert(decltype(f(c))::value == 2, "");
 338       static_assert(decltype(f(0))::value == 3, "");
 339     }
 340
 341   }
 342
 343   namespace test_uniform_initialization
 344   {
 345
 346     struct test
 347     {
 348       static const int zero {};
 349       static const int one {1};
 350     };
 351
 352     static_assert(test::zero == 0, "");
 353     static_assert(test::one == 1, "");
 354
 355   }
 356
 357   namespace test_lambdas
 358   {
 359
 360     void
 361     test1()
 362     {
 363       auto lambda1 = [](){};
 364       auto lambda2 = lambda1;
 365       lambda1();
 366       lambda2();
 367     }
 368
 369     int
 370     test2()
 371     {
 372       auto a = [](int i, int j){ return i + j; }(1, 2);
 373       auto b = []() -> int { return '0'; }();
 374       auto c = [=](){ return a + b; }();
 375       auto d = [&](){ return c; }();
 376       auto e = [a, &b](int x) mutable {
 377         const auto identity = [](int y){ return y; };
 378         for (auto i = 0; i < a; ++i)
 379           a += b--;
 380         return x + identity(a + b);
 381       }(0);
 382       return a + b + c + d + e;
 383     }
 384
 385     int
 386     test3()
 387     {
 388       const auto nullary = [](){ return 0; };
 389       const auto unary = [](int x){ return x; };
 390       using nullary_t = decltype(nullary);
 391       using unary_t = decltype(unary);
 392       const auto higher1st = [](nullary_t f){ return f(); };
 393       const auto higher2nd = [unary](nullary_t f1){
 394         return [unary, f1](unary_t f2){ return f2(unary(f1())); };
 395       };
 396       return higher1st(nullary) + higher2nd(nullary)(unary);
 397     }
 398
 399   }
 400
 401   namespace test_variadic_templates
 402   {
 403
 404     template <int...>
 405     struct sum;
 406
 407     template <int N0, int... N1toN>
 408     struct sum<N0, N1toN...>
 409     {
 410       static constexpr auto value = N0 + sum<N1toN...>::value;
 411     };
 412
 413     template <>
 414     struct sum<>
 415     {
 416       static constexpr auto value = 0;
 417     };
 418
 419     static_assert(sum<>::value == 0, "");
 420     static_assert(sum<1>::value == 1, "");
 421     static_assert(sum<23>::value == 23, "");
 422     static_assert(sum<1, 2>::value == 3, "");
 423     static_assert(sum<5, 5, 11>::value == 21, "");
 424     static_assert(sum<2, 3, 5, 7, 11, 13>::value == 41, "");
 425
 426   }
 427
 428   // http://stackoverflow.com/questions/13728184/template-aliases-and-sfinae
 429   // Clang 3.1 fails with headers of libstd++ 4.8.3 when using std::function
 430   // because of this.
 431   namespace test_template_alias_sfinae
 432   {
 433
 434     struct foo {};
 435
 436     template<typename T>
 437     using member = typename T::member_type;
 438
 439     template<typename T>
 440     void func(...) {}
 441
 442     template<typename T>
 443     void func(member<T>*) {}
 444
 445     void test();
 446
 447     void test() { func<foo>(0); }
 448
 449   }
 450
 451 }  // namespace cxx11
 452
 453 #endif  // __cplusplus >= 201103L
 454
 455 ]])
 456
 457
 458 dnl  Tests for new features in C++14
 459
 460 m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_14], [[
 461
 462 // If the compiler admits that it is not ready for C++14, why torture it?
 463 // Hopefully, this will speed up the test.
 464
 465 #ifndef __cplusplus
 466
 467 #error "This is not a C++ compiler"
 468
 469 #elif __cplusplus < 201402L
 470
 471 #error "This is not a C++14 compiler"
 472
 473 #else
 474
 475 namespace cxx14
 476 {
 477
 478   namespace test_polymorphic_lambdas
 479   {
 480
 481     int
 482     test()
 483     {
 484       const auto lambda = [](auto&&... args){
 485         const auto istiny = [](auto x){
 486           return (sizeof(x) == 1UL) ? 1 : 0;
 487         };
 488         const int aretiny[] = { istiny(args)... };
 489         return aretiny[0];
 490       };
 491       return lambda(1, 1L, 1.0f, '1');
 492     }
 493
 494   }
 495
 496   namespace test_binary_literals
 497   {
 498
 499     constexpr auto ivii = 0b0000000000101010;
 500     static_assert(ivii == 42, "wrong value");
 501
 502   }
 503
 504   namespace test_generalized_constexpr
 505   {
 506
 507     template < typename CharT >
 508     constexpr unsigned long
 509     strlen_c(const CharT *const s) noexcept
 510     {
 511       auto length = 0UL;
 512       for (auto p = s; *p; ++p)
 513         ++length;
 514       return length;
 515     }
 516
 517     static_assert(strlen_c("") == 0UL, "");
 518     static_assert(strlen_c("x") == 1UL, "");
 519     static_assert(strlen_c("test") == 4UL, "");
 520     static_assert(strlen_c("another\0test") == 7UL, "");
 521
 522   }
 523
 524   namespace test_lambda_init_capture
 525   {
 526
 527     int
 528     test()
 529     {
 530       auto x = 0;
 531       const auto lambda1 = [a = x](int b){ return a + b; };
 532       const auto lambda2 = [a = lambda1(x)](){ return a; };
 533       return lambda2();
 534     }
 535
 536   }
 537
 538   namespace test_digit_separators
 539   {
 540
 541     constexpr auto ten_million = 100'000'000;
 542     static_assert(ten_million == 100000000, "");
 543
 544   }
 545
 546   namespace test_return_type_deduction
 547   {
 548
 549     auto f(int& x) { return x; }
 550     decltype(auto) g(int& x) { return x; }
 551
 552     template < typename T1, typename T2 >
 553     struct is_same
 554     {
 555       static constexpr auto value = false;
 556     };
 557
 558     template < typename T >
 559     struct is_same<T, T>
 560     {
 561       static constexpr auto value = true;
 562     };
 563
 564     int
 565     test()
 566     {
 567       auto x = 0;
 568       static_assert(is_same<int, decltype(f(x))>::value, "");
 569       static_assert(is_same<int&, decltype(g(x))>::value, "");
 570       return x;
 571     }
 572
 573   }
 574
 575 }  // namespace cxx14
 576
 577 #endif  // __cplusplus >= 201402L
 578
 579 ]])
 580
 581
 582 dnl  Tests for new features in C++17
 583
 584 m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_17], [[
 585
 586 // If the compiler admits that it is not ready for C++17, why torture it?
 587 // Hopefully, this will speed up the test.
 588
 589 #ifndef __cplusplus
 590
 591 #error "This is not a C++ compiler"
 592
 593 #elif __cplusplus <= 201402L
 594
 595 #error "This is not a C++17 compiler"
 596
 597 #else
 598
 599 #if defined(__clang__)
 600   #define REALLY_CLANG
 601 #else
 602   #if defined(__GNUC__)
 603     #define REALLY_GCC
 604   #endif
 605 #endif
 606
 607 #include <initializer_list>
 608 #include <utility>
 609 #include <type_traits>
 610
 611 namespace cxx17
 612 {
 613
 614 #if !defined(REALLY_CLANG)
 615   namespace test_constexpr_lambdas
 616   {
 617
 618     // TODO: test it with clang++ from git
 619
 620     constexpr int foo = [](){return 42;}();
 621
 622   }
 623 #endif // !defined(REALLY_CLANG)
 624
 625   namespace test::nested_namespace::definitions
 626   {
 627
 628   }
 629
 630   namespace test_fold_expression
 631   {
 632
 633     template<typename... Args>
 634     int multiply(Args... args)
 635     {
 636       return (args * ... * 1);
 637     }
 638
 639     template<typename... Args>
 640     bool all(Args... args)
 641     {
 642       return (args && ...);
 643     }
 644
 645   }
 646
 647   namespace test_extended_static_assert
 648   {
 649
 650     static_assert (true);
 651
 652   }
 653
 654   namespace test_auto_brace_init_list
 655   {
 656
 657     auto foo = {5};
 658     auto bar {5};
 659
 660     static_assert(std::is_same<std::initializer_list<int>, decltype(foo)>::value);
 661     static_assert(std::is_same<int, decltype(bar)>::value);
 662   }
 663
 664   namespace test_typename_in_template_template_parameter
 665   {
 666
 667     template<template<typename> typename X> struct D;
 668
 669   }
 670
 671   namespace test_fallthrough_nodiscard_maybe_unused_attributes
 672   {
 673
 674     int f1()
 675     {
 676       return 42;
 677     }
 678
 679     [[nodiscard]] int f2()
 680     {
 681       [[maybe_unused]] auto unused = f1();
 682
 683       switch (f1())
 684       {
 685       case 17:
 686         f1();
 687         [[fallthrough]];
 688       case 42:
 689         f1();
 690       }
 691       return f1();
 692     }
 693
 694   }
 695
 696   namespace test_extended_aggregate_initialization
 697   {
 698
 699     struct base1
 700     {
 701       int b1, b2 = 42;
 702     };
 703
 704     struct base2
 705     {
 706       base2() {
 707         b3 = 42;
 708       }
 709       int b3;
 710     };
 711
 712     struct derived : base1, base2
 713     {
 714         int d;
 715     };
 716
 717     derived d1 {{1, 2}, {}, 4};  // full initialization
 718     derived d2 {{}, {}, 4};      // value-initialized bases
 719
 720   }
 721
 722   namespace test_general_range_based_for_loop
 723   {
 724
 725     struct iter
 726     {
 727       int i;
 728
 729       int& operator* ()
 730       {
 731         return i;
 732       }
 733
 734       const int& operator* () const
 735       {
 736         return i;
 737       }
 738
 739       iter& operator++()
 740       {
 741         ++i;
 742         return *this;
 743       }
 744     };
 745
 746     struct sentinel
 747     {
 748       int i;
 749     };
 750
 751     bool operator== (const iter& i, const sentinel& s)
 752     {
 753       return i.i == s.i;
 754     }
 755
 756     bool operator!= (const iter& i, const sentinel& s)
 757     {
 758       return !(i == s);
 759     }
 760
 761     struct range
 762     {
 763       iter begin() const
 764       {
 765         return {0};
 766       }
 767
 768       sentinel end() const
 769       {
 770         return {5};
 771       }
 772     };
 773
 774     void f()
 775     {
 776       range r {};
 777
 778       for (auto i : r)
 779       {
 780         [[maybe_unused]] auto v = i;
 781       }
 782     }
 783
 784   }
 785
 786   namespace test_lambda_capture_asterisk_this_by_value
 787   {
 788
 789     struct t
 790     {
 791       int i;
 792       int foo()
 793       {
 794         return [*this]()
 795         {
 796           return i;
 797         }();
 798       }
 799     };
 800
 801   }
 802
 803   namespace test_enum_class_construction
 804   {
 805
 806     enum class byte : unsigned char
 807     {};
 808
 809     byte foo {42};
 810
 811   }
 812
 813   namespace test_constexpr_if
 814   {
 815
 816     template <bool cond>
 817     int f ()
 818     {
 819       if constexpr(cond)
 820       {
 821         return 13;
 822       }
 823       else
 824       {
 825         return 42;
 826       }
 827     }
 828
 829   }
 830
 831   namespace test_selection_statement_with_initializer
 832   {
 833
 834     int f()
 835     {
 836       return 13;
 837     }
 838
 839     int f2()
 840     {
 841       if (auto i = f(); i > 0)
 842       {
 843         return 3;
 844       }
 845
 846       switch (auto i = f(); i + 4)
 847       {
 848       case 17:
 849         return 2;
 850
 851       default:
 852         return 1;
 853       }
 854     }
 855
 856   }
 857
 858 #if !defined(REALLY_CLANG)
 859   namespace test_template_argument_deduction_for_class_templates
 860   {
 861
 862     // TODO: test it with clang++ from git
 863
 864     template <typename T1, typename T2>
 865     struct pair
 866     {
 867       pair (T1 p1, T2 p2)
 868         : m1 {p1},
 869           m2 {p2}
 870       {}
 871
 872       T1 m1;
 873       T2 m2;
 874     };
 875
 876     void f()
 877     {
 878       [[maybe_unused]] auto p = pair{13, 42u};
 879     }
 880
 881   }
 882 #endif // !defined(REALLY_CLANG)
 883
 884   namespace test_non_type_auto_template_parameters
 885   {
 886
 887     template <auto n>
 888     struct B
 889     {};
 890
 891     B<5> b1;
 892     B<'a'> b2;
 893
 894   }
 895
 896 #if !defined(REALLY_CLANG)
 897   namespace test_structured_bindings
 898   {
 899
 900     // TODO: test it with clang++ from git
 901
 902     int arr[2] = { 1, 2 };
 903     std::pair<int, int> pr = { 1, 2 };
 904
 905     auto f1() -> int(&)[2]
 906     {
 907       return arr;
 908     }
 909
 910     auto f2() -> std::pair<int, int>&
 911     {
 912       return pr;
 913     }
 914
 915     struct S
 916     {
 917       int x1 : 2;
 918       volatile double y1;
 919     };
 920
 921     S f3()
 922     {
 923       return {};
 924     }
 925
 926     auto [ x1, y1 ] = f1();
 927     auto& [ xr1, yr1 ] = f1();
 928     auto [ x2, y2 ] = f2();
 929     auto& [ xr2, yr2 ] = f2();
 930     const auto [ x3, y3 ] = f3();
 931
 932   }
 933 #endif // !defined(REALLY_CLANG)
 934
 935 #if !defined(REALLY_CLANG)
 936   namespace test_exception_spec_type_system
 937   {
 938
 939     // TODO: test it with clang++ from git
 940
 941     struct Good {};
 942     struct Bad {};
 943
 944     void g1() noexcept;
 945     void g2();
 946
 947     template<typename T>
 948     Bad
 949     f(T*, T*);
 950
 951     template<typename T1, typename T2>
 952     Good
 953     f(T1*, T2*);
 954
 955     static_assert (std::is_same_v<Good, decltype(f(g1, g2))>);
 956
 957   }
 958 #endif // !defined(REALLY_CLANG)
 959
 960   namespace test_inline_variables
 961   {
 962
 963     template<class T> void f(T)
 964     {}
 965
 966     template<class T> inline T g(T)
 967     {
 968       return T{};
 969     }
 970
 971     template<> inline void f<>(int)
 972     {}
 973
 974     template<> int g<>(int)
 975     {
 976       return 5;
 977     }
 978
 979   }
 980
 981 }  // namespace cxx17
 982
 983 #endif  // __cplusplus <= 201402L
 984
 985 ]])