https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104113
Bug ID: 104113
Summary: DR 625 forbids "auto" being used in template argument
and parser fails to issue correct error message for it
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nickhuang99 at hotmail dot com
Target Milestone: ---
DR 625 forbids "auto" to be used in template argument. And developer has
specific error message for this and fails to issue it for the very case:
(https://www.godbolt.org/z/198fn1jr1)
template <class T> struct A {};
template <class T> void f(A<T> x) {}
void g()
{
f(A<short>());
A<auto> x = A<short>();
}
The error message is very misleading. Note that only the 2nd error message is
parser confirmed error message which is considered as conversion issue instead
of "auto" being forbidden to be in template argument. (The 1st error message is
parser tentative parsing issued.)
<source>: In function 'void g()':
<source>:14:11: error: template argument 1 is invalid
14 | A<auto> x = A<short>();
| ^
<source>:14:17: error: cannot convert 'A<short int>' to 'int' in initialization
14 | A<auto> x = A<short>();
| ^~~~~~~~~~
| |
| A<short int>
And this case can be reduced as
template<typename T>
struct A{};
A<auto> x = A<short>();
This is related to PR104091, however, it is very different because this one is
not affected by "-std=c++XX"
