Cannot compile with clang 14

[mincequi]

Hey there, i stumbled across your lib when i was searching for a performant template engine. Compiling with GCC12 is just fine. However, it fails with clang 14 on linux.

/home/minski/bustache/src/format.cpp:60: error: call to consteval function 'bustache::parser::(anonymous namespace)::constv<unsigned long>' is not a constant expression
/home/minski/bustache/src/format.cpp:60:45: error: call to consteval function 'bustache::parser::(anonymous namespace)::constv<unsigned long>' is not a constant expression
        const auto match = (... & ((ascii ^ constv(broadcast(c))) + mask)) | word;
                                            ^
/home/minski/bustache/src/format.cpp:60:62: note: subexpression not valid in a constant expression
        const auto match = (... & ((ascii ^ constv(broadcast(c))) + mask)) | word;
                                                             ^

Next thing to tackle is macOS compatiblity. clang14 from macOS does not support std::ranges. Might there be a workaround for this? In other cases, macOS users would be locked out from your lib.

Thanks and best regards

[jamboree]

I committed a patch to workaround the problem, I don't have the toolchain to test, please check if it works.

[mincequi]

Nice, one more thing:

in model.hpp you seem to forward declare std::variant. This causes the following issue:

In file included from /Users/minski/bustache/include/bustache/render.hpp:10:
/Users/minski/bustache/include/bustache/model.hpp:694:33: error: reference to 'variant' is ambiguous
    struct impl_compatible<std::variant<T...>>
                                ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk/usr/include/c++/v1/variant:1261:28: note: candidate found by name lookup is 'std::__1::variant'
class _LIBCPP_TEMPLATE_VIS variant
                           ^
/Users/minski/bustache/include/bustache/model.hpp:32:11: note: candidate found by name lookup is 'std::variant'
    class variant;
          ^
/Users/minski/bustache/include/bustache/model.hpp:696:45: error: reference to 'variant' is ambiguous
        static value_ptr get_value_ptr(std::variant<T...> const& self)
                                            ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk/usr/include/c++/v1/variant:1261:28: note: candidate found by name lookup is 'std::__1::variant'
class _LIBCPP_TEMPLATE_VIS variant
                           ^
/Users/minski/bustache/include/bustache/model.hpp:32:11: note: candidate found by name lookup is 'std::variant'
    class variant;
          ^
2 errors generated.

Simply including <variant> in model.hpp fixes the issue for me:

 #include <functional>
+#include <variant>
 #ifdef BUSTACHE_USE_FMT
 #include <fmt/format.h>
 #elif defined(__cpp_lib_format)
@@ -26,11 +27,13 @@
 #include <iterator>
 #endif

+/*
 namespace std
 {
     template<class... T>
     class variant;
 };
+*/

What do you think?

[jamboree]

Because the use of std::variant is optional, I tried to avoid unnecessary include if the user doesn't use it. But technically speaking, one should not forward declare standard types 😥. What you proposed is absolutely right.