libcxx/test/support/concat_macros.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef TEST_SUPPORT_CONCAT_MACROS_H
  10 #define TEST_SUPPORT_CONCAT_MACROS_H
  11
  12 #include <cstdio>
  13 #include <string>
  14
  15 #include "assert_macros.h"
  16 #include "test_macros.h"
  17
  18 #ifndef TEST_HAS_NO_LOCALIZATION
  19 #  include <sstream>
  20 #endif
  21
  22 #if TEST_STD_VER > 17
  23
  24 #  ifndef TEST_HAS_NO_LOCALIZATION
  25 template <class T>
  26 concept test_char_streamable = requires(T&& value) { std::stringstream{} << std::forward<T>(value); };
  27 #  endif
  28
  29 // If possible concatenates message for the assertion function, else returns a
  30 // default message. Not being able to stream is not considered and error. For
  31 // example, streaming to std::wcerr doesn't work properly in the CI. Therefore
  32 // the formatting tests should only stream to std::string.
  33 //
  34 // The macro TEST_WRITE_CONCATENATED can be used to evaluate the arguments
  35 // lazily. This useful when using this function in combination with
  36 // assert_macros.h.
  37 template <class... Args>
  38 std::string test_concat_message([[maybe_unused]] Args&&... args) {
  39 #  ifndef TEST_HAS_NO_LOCALIZATION
  40   if constexpr ((test_char_streamable<Args> && ...)) {
  41     std::stringstream sstr;
  42     ((sstr << std::forward<Args>(args)), ...);
  43     return sstr.str();
  44   } else
  45 #  endif
  46     return "Message discarded since it can't be streamed to std::cerr.\n";
  47 }
  48
  49 // Writes its arguments to stderr, using the test_concat_message helper.
  50 #  define TEST_WRITE_CONCATENATED(...) [&] { ::test_eprintf("%s", ::test_concat_message(__VA_ARGS__).c_str()); }
  51
  52 #endif // TEST_STD_VER > 17
  53
  54 #endif //  TEST_SUPPORT_CONCAT_MACROS_H