I met an incorrect ODR checks caused by preferred_name. Here is a reduced example.

// string_view.h template<class _CharT> class basic_string_view; typedef basic_string_view<char> string_view; template<class _CharT> class __attribute__((__preferred_name__(string_view))) basic_string_view { public: basic_string_view() { } }; inline basic_string_view<char> foo() { return basic_string_view<char>(); } // A.cppm module; #include "string_view.h" export module A; // Use.cppm module; #include "string_view.h" export module Use; import A;

The input command line is:

clang++ -std=c++20 --precompile A.cppm -o A.pcm clang++ -std=c++20 --precompile Use.cppm -fprebuilt-module-path=. -fsyntax-only

The output would be the incorrect ODR warning:

string_view.h:11:5: error: 'basic_string_view<char>::basic_string_view' from module 'A.<global>' is not present in definition of 'string_view' provided earlier

I've been fighting with the problem for several days. My current process is that when the ASTReader reads the preferred_name attribute, it would read the string_view type and find an existing one. However, the current behavior would create another RecordType for string_view despite there is already one. So here is the problem.