https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125108
Bug ID: 125108
Summary: [reflection] template_arguments_of gives underlying
entity of alias template
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jolly.j.chen at gmail dot com
Target Milestone: ---
template_arguments_of returns the reflection of the underlying entity of an
alias template A instead of the reflection of A. For example
(https://godbolt.org/z/n17bE3dnq):
template<typename T> using underlying_alias = T;
template<typename T> using alias = underlying_alias<T>;
template <template <class> class> struct Test
static_assert(^^alias != ^^underlying_alias);
static_assert(template_arguments_of(^^Test<alias>)[0] == ^^alias);
fails with
error: static assertion failed
19 | static_assert(template_arguments_of(^^Test<alias>)[0] == ^^alias);
• the comparison reduces to '(^^underlying_alias == ^^alias)'
I believe https://eel.is/c++draft/meta.reflection#queries-59.2 states that
template_arguments_of should return ^^alias here. This is also what Clang does.
