Compilation errors with single-source branch and clang

[StewMH]

Compiling with clang and the single source file included gives me these errors:

In file included from <source>:4:
/app/raw.githubusercontent.com/alpaka-group/alpaka/single-header/include/alpaka/alpaka.hpp:26621:67: error: template template argument has different template parameters than its corresponding template template parameter
 26621 |             using EnabledAccTags = alpaka::meta::Filter<AccTags, alpaka::AccIsEnabled>;
       |                                                                          ^
/app/raw.githubusercontent.com/alpaka-group/alpaka/single-header/include/alpaka/alpaka.hpp:26610:6: note: too many template parameters in template template argument
 26610 |             template<typename TTag, typename = void>
       |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/app/raw.githubusercontent.com/alpaka-group/alpaka/single-header/include/alpaka/alpaka.hpp:26596:32: note: previous template template parameter is here
 26596 |                     template<typename TList, template<typename> class TPred>
       |                                              ^~~~~~~~~~~~~~~~~~
1 error generated.
Compiler returned: 1

https://godbolt.org/z/9ffdPPKzj

I could not find a clang version that it worked for.

[StewMH]

I think this is the offending commit:
eae316f
Just confusing myself now, ignore this. Haven't figured out where it fails.

[SimeonEhrig]

The reason is, that we use a C++17 feature, which is disable by default until Clang 18. Clang 19 will enable it by default. Please set the compiler flag -frelaxed-template-template-args.

For more details, see here:

alpaka/cmake/alpakaCommon.cmake

Lines 197 to 202 in 887aee9

	# C++17 relaxed template template argument matching is disabled by default until Clang 19
	# https://github.com/llvm/llvm-project/commit/b86e0992bfa6
	# https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#150
	# for example, is required to create alpaka::EnabledAccTags
	# the feature is implemented since Clang 4
	alpaka_set_compiler_options(HOST_DEVICE target alpaka "$<$<AND:$<CXX_COMPILER_ID:Clang,AppleClang,IntelLLVM>>:SHELL:-frelaxed-template-template-args>")

[psychocoderHPC]

We added -frelaxed-template-template-args to alpaka with #2267

The provided godbolt example works fine when adding -frelaxed-template-template-args, therefor I will close this issue.