feat: unsatisfied added and enabled throwing constraints

src/CMakeLists.txt

@@ -50,6 +50,7 @@ endif()
 # check for C++ features
 check_cxx_feature_supported(__cpp_lib_format ${projectPrefix}LIB_FORMAT_SUPPORTED)
 check_cxx_feature_supported(__cpp_explicit_this_parameter ${projectPrefix}EXPLICIT_THIS_PARAMETER_SUPPORTED)
+check_cxx_feature_supported("__cpp_constexpr_exceptions >= 202411L" ${projectPrefix}CONSTEXPR_EXCEPTIONS_SUPPORTED)
 
 # libc++ has a basic supports for std::format but does not set __cpp_lib_format
 # https://github.com/llvm/llvm-project/issues/77773
@@ -80,12 +81,16 @@ option(${projectPrefix}API_STD_FORMAT "Enable `std::format` support" ${${project
 option(${projectPrefix}API_NO_CRTP "Enable class definitions without CRTP idiom"
        ${${projectPrefix}EXPLICIT_THIS_PARAMETER_SUPPORTED}
 )
+option(${projectPrefix}API_THROWING_CONSTRAINTS "Enable throwing constraints"
+       ${projectPrefix}CONSTEXPR_EXCEPTIONS_SUPPORTED
+)
 option(${projectPrefix}API_FREESTANDING "Builds only freestanding part of the library" OFF)
 set(${projectPrefix}API_CONTRACTS GSL-LITE CACHE STRING "Enable contract checking")
 check_cache_var_values(API_CONTRACTS NONE GSL-LITE MS-GSL)
 
 message(STATUS "${projectPrefix}API_STD_FORMAT: ${${projectPrefix}API_STD_FORMAT}")
 message(STATUS "${projectPrefix}API_NO_CRTP: ${${projectPrefix}API_NO_CRTP}")
+message(STATUS "${projectPrefix}API_THROWING_CONSTRAINTS: ${${projectPrefix}API_THROWING_CONSTRAINTS}")
 message(STATUS "${projectPrefix}API_FREESTANDING: ${${projectPrefix}API_FREESTANDING}")
 message(STATUS "${projectPrefix}API_CONTRACTS: ${${projectPrefix}API_CONTRACTS}")
 

src/core/CMakeLists.txt

@@ -42,6 +42,7 @@ add_mp_units_module(
             include/mp-units/bits/text_tools.h
             include/mp-units/bits/type_list.h
             include/mp-units/bits/unit_magnitude.h
+            include/mp-units/bits/unsatisfied.h
             include/mp-units/ext/algorithm.h
             include/mp-units/ext/contracts.h
             include/mp-units/ext/fixed_string.h
@@ -162,6 +163,14 @@ target_compile_definitions(
                   ${projectPrefix}HOSTED=$<NOT:$<BOOL:${${projectPrefix}API_FREESTANDING}>>
 )
 
+# Throwing constraints
+if(${projectPrefix}API_THROWING_CONSTRAINTS)
+    target_compile_definitions(
+        mp-units-core ${${projectPrefix}TARGET_SCOPE}
+                      ${projectPrefix}API_THROWING_CONSTRAINTS=$<BOOL:${${projectPrefix}API_THROWING_CONSTRAINTS}>
+    )
+endif()
+
 # https://github.com/llvm/llvm-project/issues/131410
 if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 20
    AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 20.2

src/core/include/mp-units/bits/unsatisfied.h

@@ -0,0 +1,71 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+#include <mp-units/bits/constexpr_format.h>
+#include <mp-units/bits/hacks.h>  // IWYU pragma: keep
+#include <mp-units/ext/fixed_string.h>
+
+#if MP_UNITS_API_THROWING_CONSTRAINTS
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#ifdef MP_UNITS_IMPORT_STD
+import std;
+#else
+#include <stdexcept>
+#include <string>
+#endif
+#endif
+#endif
+
+namespace mp_units::detail {
+
+#if MP_UNITS_API_THROWING_CONSTRAINTS
+
+#if __cpp_lib_constexpr_exceptions
+
+struct unsatisfied_constraints : std::logic_error {
+  consteval explicit unsatisfied_constraints(const std::string& msg) : std::logic_error(msg) {}
+  [[nodiscard]] constexpr const char* what() const noexcept override { return std::logic_error::what(); }
+};
+
+#else
+
+struct unsatisfied_constraints {
+  std::string msg;
+  [[nodiscard]] consteval const char* what() const noexcept { return msg.c_str(); }
+};
+
+#endif
+
+#endif
+
+template<mp_units::fixed_string Fmt, typename... Args>
+[[nodiscard]] consteval bool unsatisfied([[maybe_unused]] Args&&... args)
+{
+#if MP_UNITS_API_THROWING_CONSTRAINTS
+  throw unsatisfied_constraints{constexpr_format(FMT_COMPILE(Fmt.c_str()), std::forward<Args>(args)...)};
+#endif
+  return false;
+}
+
+}  // namespace mp_units::detail