From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 731AB3858D38; Sat,  6 Apr 2024 02:37:29 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 731AB3858D38
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1712371049;
	bh=8AHhMXVxUVP+HLRG+ILkeTUEWjTBDcAfQivOyFZV/QM=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=puQT8ftZ8yDQJ7ghvro1fBQBbX+eQa2QO4pPjsiDyzZgUR3I/L+gt1CBlPl1dagHn
	 QpOYxQXFoM1ovziu00sLBRzdKmuiQS3AEborhwnUBFdGT4gt+JSYT6oizipydmaDH2
	 F3MOeww9ly+klURebGvM+F5cqXZujOsxQabSExAg=
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/91798] Compiler rejects code due to template specialization
 of auto parameter value.
Date: Sat, 06 Apr 2024 02:37:27 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 8.1.0
X-Bugzilla-Keywords: rejects-valid
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-91798-4-XTNZT7KPrp@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-91798-4@http.gcc.gnu.org/bugzilla/>
References: <bug-91798-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D91798

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually maybe GCC is correct here.
Remove the variadic template:
```
//Get type parameter at given index.
template<auto i>
struct param
{
    static_assert(i > 0, "Index into parameter pack cannot be negative!");
    using type =3D typename param<i - 1>::type;
};

template<>
struct param<0>
{
    using type =3D int;
};

int main()
{
    typename param<0u>::type x =3D 'a';
    static_cast<void>(x);
}
```

Every compiler (EDG, GCC, clang and MSVC) I tried rejects this.

Note the original code,  EDG rejects it for the same reason as GCC.

The reason why is 0 is different 0u as they have different types as they sh=
ould
not match.

Though I think there is a defect report in that area ...=