declaration of included invalid class template cause crash

[Amir Maimon]

*** system details ***

Ubuntu 20.04.1 LTS
g++-10 (Ubuntu 10.2.0-5ubuntu1~20.04) 10.2.0

*** compilation line ***
g++-10 -std=c++20 internal_repro.cpp

*** output ***

internal_repro.cpp:4:4: internal compiler error: in coerce_template_parms, at cp/pt.c:8971
    4 | A<T> a;
      | ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-10/README.Bugs> for instructions.

*** code ***

internal_repro.h:

template <undeclared_concept T>
class A{};

internal_repro.cpp:

#include "internal_repro.h"
template <typename T>
A<T> a;

[Amir Maimon (amirmaimoncs)]

compilation line that created the attached files include "-save-temps"

g++-10 -std=c++20 internal_repro.cpp -save-temps

[Matthias Klose (doko)]

can't reproduce, I get:

$ g++-10 -std=c++20 internal_repro.cpp
In file included from internal_repro.cpp:1:
internal_repro.h:1:11: error: ‘undeclared_concept’ has not been declared
    1 | template <undeclared_concept T>
      | ^~~~~~~~~~~~~~~~~~

$ g++-10 --version
g++-10 (Ubuntu 10.2.0-5ubuntu1~20.04) 10.2.0

[Launchpad Janitor (janitor)]

[Expired for gcc-10 (Ubuntu) because there has been no activity for 60 days.]