C++ modules example fails on LLVM 15.0.7 for 64-bit Windows - delayed template parsing is not supported/broken with C++ modules #61068
Description
The documentation here provides the following Hello-World style example:
// M.cppm
export module M;
export import :interface_part;
import :impl_part;
export void Hello();
// interface_part.cppm
export module M:interface_part;
export void World();
// impl_part.cppm
module;
#include <iostream>
#include <string>
module M:impl_part;
import :interface_part;
std::string W = "World.";
void World() {
std::cout << W << std::endl;
}
// Impl.cpp
module;
#include <iostream>
module M;
void Hello() {
std::cout << "Hello ";
}
// User.cpp
import M;
int main() {
Hello();
World();
return 0;
}Precompiling the module
clang++ -std=c++20 interface_part.cppm --precompile -o M-interface_part.pcm
clang++ -std=c++20 impl_part.cppm --precompile -fprebuilt-module-path=. -o M-impl_part.pcm
clang++ -std=c++20 M.cppm --precompile -fprebuilt-module-path=. -o M.pcm
clang++ -std=c++20 Impl.cpp -fmodule-file=M.pcm -c -o Impl.oCompiling the user
clang++ -std=c++20 User.cpp -fprebuilt-module-path=. -c -o User.oCompiling the module and linking it together
clang++ -std=c++20 M-interface_part.pcm -c -o M-interface_part.o
clang++ -std=c++20 M-impl_part.pcm -c -o M-impl_part.o
clang++ -std=c++20 M.pcm -c -o M.o
clang++ User.o M-interface_part.o M-impl_part.o M.o Impl.o -o a.outI tried this exact example on LLVM 15.0.7 for 64-bit Windows. The files are included. The standard library and linker/backend in my environment is MSVC 17.5.1. I have changed the command lines slightly for Windows. The result is a strange failure at Impl.cpp:
Impl.cpp:5:3: error: use of undeclared identifier 'std'
std::cout << "Hello ";
^
1 error generated.Note, I can compile, link and execute a regular "Hello World" (without C++20 modules) in my LLVM environment just fine, it is only behaving this way when it imports modules and includes system headers in global module fragments of those imported modules.
test2.zip