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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107428] New: trying to define a partial specialized concept
 does not give a good error message
Date: Wed, 26 Oct 2022 20:45:30 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: diagnostic
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pinskia at gcc dot gnu.org
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107428

            Bug ID: 107428
           Summary: trying to define a partial specialized concept does
                    not give a good error message
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
template<typename T, typename T1>
concept same =3D false;
template<typename T>
concept same<T, T> =3D true;
```

GCC produces:
```
<source>:6:13: error: expected '=3D' before '<' token
    6 | concept same<T, T> =3D true;
      |             ^
```

While clang produces:
```
<source>:6:9: error: name defined in concept definition must be an identifi=
er
concept same<T, T> =3D true;
        ^
```

While clang is definitely better than GCC. We could do even better at
sugguesting you can't do a partial specialization of a concept.=