Build Failure with clang++ 20

[e-kwsm]

Describe the bug
Catch does not build with clang++ 20.

Expected behavior
Catch successfully builds.

Reproduction steps
Steps to reproduce the bug.

$ CXX=clang++ cmake -S . -B build -DCATCH_DEVELOPMENT_BUILD=ON
$ cmake --build build -- -k
[ 63%] Built target Catch2
[ 64%] Built target Catch2WithMain
[ 64%] Building CXX object tests/CMakeFiles/SelfTest.dir/SelfTest/UsageTests/Generators.tests.cpp.o
tests/SelfTest/UsageTests/Generators.tests.cpp:303:18: error: 'return' will never be executed [-Werror,-Wunreachable-code-return]
  303 |         return { new test_generator() };
      |                  ^~~~~~~~~~~~~~~~~~~~
1 error generated.
make[2]: *** [tests/CMakeFiles/SelfTest.dir/build.make:653: tests/CMakeFiles/SelfTest.dir/SelfTest/UsageTests/Generators.tests.cpp.o] Error 1
[ 65%] Building CXX object tests/CMakeFiles/SelfTest.dir/SelfTest/UsageTests/Misc.tests.cpp.o
tests/SelfTest/UsageTests/Misc.tests.cpp:387:1: error: no matching function for call to 'get_wrapper'
  387 | TEMPLATE_PRODUCT_TEST_CASE("Product with differing arities", "[template][product]", std::tuple, (int, (int, double), (int, double, float))) {
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/catch2/../catch2/catch_template_test_macros.hpp:80:47: note: expanded from macro 'TEMPLATE_PRODUCT_TEST_CASE'
   80 |     #define TEMPLATE_PRODUCT_TEST_CASE( ... ) INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE( __VA_ARGS__ )
      |                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/catch2/../catch2/internal/catch_template_test_registry.hpp:155:9: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE'
  155 |         INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2(INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), Name, Tags, typename T,__VA_ARGS__)
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/catch2/../catch2/internal/catch_template_test_registry.hpp:142:69: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2'
  142 |                 using TestInit = typename create<TestName, decltype(get_wrapper<INTERNAL_CATCH_REMOVE_PARENS(TmplTypes)>()), TypeList<INTERNAL_CATCH_MAKE_TYPE_LISTS_FROM_TYPES(INTERNAL_CATCH_REMOVE_PARENS(TypesList))>>::type; \
      |                                                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tests/SelfTest/UsageTests/Misc.tests.cpp:387:1: note: candidate template ignored: substitution failure [with Cs = <std::tuple>]: conflicting deduction 'std::tuple' against 'type-parameter-0-0' for parameter
src/catch2/../catch2/catch_template_test_macros.hpp:80:47: note: expanded from macro 'TEMPLATE_PRODUCT_TEST_CASE'
   80 |     #define TEMPLATE_PRODUCT_TEST_CASE( ... ) INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE( __VA_ARGS__ )
      |                                               ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:155:9: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE'
  155 |         INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2(INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), Name, Tags, typename T,__VA_ARGS__)
      |         ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:128:13: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2'
  128 |             INTERNAL_CATCH_TYPE_GEN                                                  \
      |             ^
src/catch2/../catch2/internal/catch_preprocessor.hpp:108:20: note: expanded from macro 'INTERNAL_CATCH_TYPE_GEN'
  108 |     constexpr auto get_wrapper() noexcept -> TemplateTypeList<Cs...> { return {}; }\
      |                    ^
tests/SelfTest/UsageTests/Misc.tests.cpp:387:1: note: candidate template ignored: invalid explicitly-specified argument for template parameter 'Ts'
src/catch2/../catch2/catch_template_test_macros.hpp:80:47: note: expanded from macro 'TEMPLATE_PRODUCT_TEST_CASE'
   80 |     #define TEMPLATE_PRODUCT_TEST_CASE( ... ) INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE( __VA_ARGS__ )
      |                                               ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:155:9: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE'
  155 |         INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2(INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), Name, Tags, typename T,__VA_ARGS__)
      |         ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:128:13: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2'
  128 |             INTERNAL_CATCH_TYPE_GEN                                                  \
      |             ^
src/catch2/../catch2/internal/catch_preprocessor.hpp:105:20: note: expanded from macro 'INTERNAL_CATCH_TYPE_GEN'
  105 |     constexpr auto get_wrapper() noexcept -> TypeList<Ts...> { return {}; }\
      |                    ^
tests/SelfTest/UsageTests/Misc.tests.cpp:387:1: error: expected a qualified name after 'typename'
  387 | TEMPLATE_PRODUCT_TEST_CASE("Product with differing arities", "[template][product]", std::tuple, (int, (int, double), (int, double, float))) {
      | ^
src/catch2/../catch2/catch_template_test_macros.hpp:80:47: note: expanded from macro 'TEMPLATE_PRODUCT_TEST_CASE'
   80 |     #define TEMPLATE_PRODUCT_TEST_CASE( ... ) INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE( __VA_ARGS__ )
      |                                               ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:155:9: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE'
  155 |         INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2(INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), Name, Tags, typename T,__VA_ARGS__)
      |         ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:142:43: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2'
  142 |                 using TestInit = typename create<TestName, decltype(get_wrapper<INTERNAL_CATCH_REMOVE_PARENS(TmplTypes)>()), TypeList<INTERNAL_CATCH_MAKE_TYPE_LISTS_FROM_TYPES(INTERNAL_CATCH_REMOVE_PARENS(TypesList))>>::type; \
      |                                           ^
tests/SelfTest/UsageTests/Misc.tests.cpp:387:1: error: expected ';' after alias declaration
src/catch2/../catch2/catch_template_test_macros.hpp:80:47: note: expanded from macro 'TEMPLATE_PRODUCT_TEST_CASE'
   80 |     #define TEMPLATE_PRODUCT_TEST_CASE( ... ) INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE( __VA_ARGS__ )
      |                                               ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:155:9: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE'
  155 |         INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2(INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), Name, Tags, typename T,__VA_ARGS__)
      |         ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:142:218: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2'
  142 |                 using TestInit = typename create<TestName, decltype(get_wrapper<INTERNAL_CATCH_REMOVE_PARENS(TmplTypes)>()), TypeList<INTERNAL_CATCH_MAKE_TYPE_LISTS_FROM_TYPES(INTERNAL_CATCH_REMOVE_PARENS(TypesList))>>::type; \
      |                                                                                                                                                                                                                          ^
tests/SelfTest/UsageTests/Misc.tests.cpp:387:1: error: unknown type name 'TestInit'
src/catch2/../catch2/catch_template_test_macros.hpp:80:47: note: expanded from macro 'TEMPLATE_PRODUCT_TEST_CASE'
   80 |     #define TEMPLATE_PRODUCT_TEST_CASE( ... ) INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE( __VA_ARGS__ )
      |                                               ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:155:9: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE'
  155 |         INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2(INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), INTERNAL_CATCH_UNIQUE_NAME( CATCH2_INTERNAL_TEMPLATE_TEST_ ), Name, Tags, typename T,__VA_ARGS__)
      |         ^
src/catch2/../catch2/internal/catch_template_test_registry.hpp:143:17: note: expanded from macro 'INTERNAL_CATCH_TEMPLATE_PRODUCT_TEST_CASE2'
  143 |                 TestInit t;                                           \
      |                 ^
4 errors generated.
make[2]: *** [tests/CMakeFiles/SelfTest.dir/build.make:681: tests/CMakeFiles/SelfTest.dir/SelfTest/UsageTests/Misc.tests.cpp.o] Error 1
make[2]: Target 'tests/CMakeFiles/SelfTest.dir/build' not remade because of errors.
make[1]: *** [CMakeFiles/Makefile2:1121: tests/CMakeFiles/SelfTest.dir/all] Error 2
make[1]: Target 'all' not remade because of errors.
make: *** [Makefile:166: all] Error 2
make: Target 'default_target' not remade because of errors.

First error occurs at

Catch2/tests/SelfTest/UsageTests/Generators.tests.cpp

Line 303 in 1de7d0e

return { new test_generator() };

which calls constructor that throws

Catch2/tests/SelfTest/UsageTests/Generators.tests.cpp

Lines 287 to 291 in 1de7d0e

	[[noreturn]] explicit test_generator() {
	// removing the following line will cause the program to terminate
	// gracefully.
	throw Catch::GeneratorException( "failure to init" );
	}

Second error (#2981) occurs at

Catch2/tests/SelfTest/UsageTests/Misc.tests.cpp

Lines 387 to 389 in 1de7d0e

	TEMPLATE_PRODUCT_TEST_CASE("Product with differing arities", "[template][product]", std::tuple, (int, (int, double), (int, double, float))) {
	REQUIRE(std::tuple_size<TestType>::value >= 1);
	}

Platform information:

• OS: EndeavourOS
• Compiler+version: clang++ 20.1.6
• Catch version: 1de7d0e

[ChrisThrasher]

I took at a look at this and am not sure quite sure what the fix is. The test code is a bit contrived because it's trying to recreate a real world possibility. Clang is correct to flag this, but idk how to make the test code not contrived while maintaining the behavior it's testing.