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From: "johelegp at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/103339] New: [modules] ICE in exporting module on use of
 outside specialization
Date: Sat, 20 Nov 2021 06:36:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103339

            Bug ID: 103339
           Summary: [modules] ICE in exporting module on use of outside
                    specialization
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: johelegp at gmail dot com
                CC: johelegp at gmail dot com
  Target Milestone: ---

See https://godbolt.org/z/onW6h5vej.

mod.cpp:
```C++
export module mod;
export template<class T> struct trait { };
export template<class> concept C =3D true;
template<class T> concept has_trait =3D C<trait<T>>;
```

test.cpp:
```C++
import mod;
template<C T> struct trait<T> { };
```

Output:
```
test.cpp:2:31: internal compiler error: in import_entity_index, at
cp/module.cc:3953
    2 | template<C T> struct trait<T> { };
      |                               ^
0x206aac9 internal_error(char const*, ...)
        ???:0
0x7d92db fancy_abort(char const*, int, char const*)
        ???:0
0x966072 module_may_redeclare(tree_node*)
        ???:0
0xaab517 begin_class_definition(tree_node*)
        ???:0
0xa0b065 c_parse_file()
        ???:0
0xb931d2 c_common_parse_file()
        ???:0
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
```

Workaround:
```diff
-template<class T> concept has_trait =3D C<trait<T>>;
+template<class T> concept has_trait =3D C<trait<std::type_identity_t<T>>>;
```

As per the logic in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99631#c1=
, this
isn't marked with any of the ice-* keywords.=