https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112737
--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Ah, this seems to be a general declaration matching issue not specific to
modules. Here's a non-modules testcase:
template<template<class> class TT, class T>
decltype(TT{T()}) f(); // #1
template<template<class> class TT, class T>
decltype(TT{T()}) f(); // #2, should be considered a redeclaration of #1
template<class T> struct A { A(T); };
int main() {
f<A, int>(); // ambiguity error
}
We (wrongly?) consider the return types of the two f's to be different, because
the CTAD placeholders refer to different TEMPLATE_DECLs (of a logically
equivalent ttp) and structural_comptypes uses pointer identity here. Perhaps
we need to relax structural_comptypes in this case.
