[GNATS 24180] Spurious diagnostic for more than one std:begin matches the argument list

[jhsedg]

Customer bug ID

coroutine2/test/test_coroutine_asm.test/test_coroutine.cpp, gnats/24180 (full preprocessed), gnats/24180a (reducded)

Description

​This is the reduced test case below. Note that the full preprocessed test case has an addition error message for more than one instance of std:end matches the funciton template.
​
​//type:fp
​//options_all:--gnu_version 80100 --c++17 -tused -w
​template class pull_coroutine {
​public:
​ template pull_coroutine(Fn);
​ class iterator {
​ public:
​ bool operator!=(iterator);
​ void operator++();
​ int operator*();
​ };
​};
​template
​typename pull_coroutine::iterator begin(pull_coroutine);
​template
​typename pull_coroutine::iterator end(pull_coroutine);
​namespace std {
​template void begin(pull_coroutine);
​}
​struct coroutine {
​ using pull_type = pull_coroutine;
​};
​void f16() {
​ coroutine::pull_type coro(6);
​ for (auto i : coro)
​ ;
​}
​
​
​fe_only -DTEST_NUMBER=1 --gnu_version 80100 --c++17 -tused -w Test_name.c
​"Test_name.c", line 25: error: more than one instance of "begin" matches the
​ argument list:
​ function template "void std::begin(pull_coroutine)" (declared at
​ line 18)
​ function template "pull_coroutine::iterator
​ begin(pull_coroutine)" (declared at line 14)
​ argument types are: (coroutine::pull_type)
​ for (auto i : coro)
​ ^
​
​1 error detected in the compilation of "Test_name.c".
​24180a.C:fp::FAIL--NO PREVIOUS OUTPUT:

Notes

​ellen, 2021-12-09:
​Boost 1_78_0 the complete test case now passes.