experimental/meta file not found

[bshafi]

Describe the bug
I'm attempting to build this compiler to try out the C++26 reflection however I can't seem to get any examples to compile.
The issue each time is that fatal error: 'experimental/meta' file not found. I'm not sure what compile option I need to add so that it compiles.

I have searched for the meta header file with find | grep "meta" in the folder where I built clang and it returns no results which makes me think that there may be an option in the build steps that I have not enabled that keeps experimental/meta from being added to the final build.

I have confirmed that experimental/meta is in the repository.

To Reproduce
Building clang

mkdir build
cd build
cmake -G "Visual Studio 17" -DLLVM_ENABLE_PROJECTS=clang -DCMAKE_BUILD_TYPE=Release ..\llvm
cmake --build .

Compile the code

clang.exe -freflection -std=c++26 -fexpansion-statements .\main.cpp -o main.exe

Result:

.\main.cpp:1:10: fatal error: 'experimental/meta' file not found
    1 | #include <experimental/meta>
      |          ^~~~~~~~~~~~~~~~~~~
1 error generated.

Code that I'm trying to compile: main.cpp

#include <experimental/meta>

#include <iostream>
#include <string>

template <typename E>
  constexpr std::string enum_to_string(E value) {
	    template for (constexpr auto e : std::meta::members_of(^E)) {
		        if (value == [:e:]) {
				      return std::string(std::meta::name_of(e));
				          }
			  }

	      return "<unnamed>";
  }

enum Color { red, green, blue };

int main() {
	std::cout << enum_to_string(Color::red) << std::endl;
}

Expected behavior
The code should build and when I run it, it should print red.

Environment (please complete the following information):
Windows 10
Visual Studio 17

I've tried almost all variants of these instructions. I've compiled the code with clang.exe -freflection -std=c++26 -fexpansion-statements -fparameter-reflection -fexpansion-statements -fconsteval-blocks -freflection-new-syntax -freflection-latest .\main.cpp -o main.exe. I've removed the #include <experimental/meta> and tried to compile it.

[Yaraslaut]

You need to build clang and libc++, you can check out this docker file https://github.com/simdjson/experimental_json_builder/blob/main/Dockerfile

And then change standard library that compiler uses to libc++, instead of libstdc++ on linux and whatever is on windows
Here is a compiler option that you set via cmake

target_compile_options($project_name INTERFACE  -freflection -stdlib=libc++ -std=c++26)

[bshafi]

Thanks for the reply! I am currently stuck trying to get libc++ on windows. I get an error unused argument -stdlib=libc++. I have tried different methods to get it to compile with clang and they don't work. I'm going to close this issue for now. If any windows user wants to document how they got libc++ to compile and work this issue can be reopened.

[YiRanMushroom]

Hello, I just saw this issue when I was struggling to find ways to compile programs on Windows. I would like to know whether you found any ways to make this work on Windows.

I compiled clang successfully but I don't think the libc++ was compiled. I used

cmake -DLLVM_ENABLE_PROJECTS="clang" -G "Visual Studio 17 2022" -Thost=x64 ..\llvm -DLLVM_HOST_TRIPLE=x86_64 -DLLVM_RUNTIME_TARGETS=x86_64 -DLLVM_ENABLE_RUNTIMES="libc;libcxx" -DCMAKE_INSTALL_PREFIX="E:/llvm-reflect" -DLLVM_PARALLEL_COMPILE_JOBS=32 -DLLVM_PARALLEL_LINK_JOBS=32 -DLLVM_PARALLEL_TABLEGEN_JOBS=32

to generate msvc sln files and used msvc to build clang. I also ran the build_all and install task but I encountered several compilation errors, and I also don't think the libc++ files were generated successfully.

When I used clang++ to compile programs, it reported that experimental/meta file not found. I also tried to add some files in libcxx, but there are still some missing files.

If you have already found a way to make this work, could you please document the process here? And if you haven't could you consider reopening this issue so that we could probably get more support on resolving this issue? Thank you.

[bshafi]

No problem.
I'm no longer actively trying to work on this issue so I won't be responding much.