[cxx-interop] Fix linker errors when a template is used from different modules #42222
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…t modules If a templated C++ class is used from two different C++ modules, and those modules are included in Swift, Clang will create different two different redecls for the class & its methods. For each of the methods, only one of the redecls would actually have a body, the other would have empty bodies. That prevents `ClangDeclFinder` from properly finding the symbols referenced from a method body, leading to a linker error in some cases, when the first redecl is missing a body. This prevents `std::string` from being used on Linux: ``` /tmp/use-std-string-2dd593.o:use-std-string-2dd593.o:function void std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_construct<char*>(char*, char*, std::forward_iterator_tag): error: undefined reference to 'bool __gnu_cxx::__is_null_pointer<char>(char*)' /tmp/use-std-string-2dd593.o:use-std-string-2dd593.o:function void std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_construct<char*>(char*, char*, std::forward_iterator_tag): error: undefined reference to 'std::iterator_traits<char*>::difference_type std::distance<char*>(char*, char*)' clang-13: error: linker command failed with exit code 1 (use -v to see invocation) <unknown>:0: error: link command failed with exit code 1 (use -v to see invocation) ```
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If a templated C++ class is used from two different C++ modules, and those modules are included in Swift, Clang will create different two different redecls for the class & its methods.
For each of the methods, only one of the redecls would actually have a body, the other would have empty bodies. That prevents
ClangDeclFinderfrom properly finding the symbols referenced from a method body, leading to a linker error in some cases, when the first redecl is missing a body.This prevents
std::stringfrom being used on Linux: