https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110409
Bug ID: 110409
Summary: ICE on explicit instantiation of undefined template
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: stevenxia990430 at gmail dot com
Target Milestone: ---
The following invalid program reports an internal compiler error: tree check:
accessed elt 2 of 'tree_vec' with 1 elts in tsubst, at cp/pt.cc:16072 on
gcc-trunk
To quickly reproduce: https://gcc.godbolt.org/z/4KcExh49f
```
template <typename E, typename F>
struct expected3 {};
template <typename E>
struct expected3<E, E>;
template <typename R, typename E>
struct expected3<R, R> {};
template struct expected3<int, int>;
int main() {
return 0;
}
```
Note after removing `template struct expected3<int, int>;` and this invalid
program:
```
template <typename E, typename F>
struct expected3 {};
template <typename E>
struct expected3<E, E>;
template <typename R, typename E>
struct expected3<R, R> {};
int main() {
return 0;
}
```
compiles successfully on gcc-trunk but is rejected on clang-trunk. See this
link: https://gcc.godbolt.org/z/9rP3vYW6o
