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* [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template
@ 2022-05-16 21:35 hello at josephloser dot com
2022-05-16 21:42 ` [Bug c++/105623] " mpolacek at gcc dot gnu.org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: hello at josephloser dot com @ 2022-05-16 21:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623
Bug ID: 105623
Summary: [12/13 regression][rejects valid] invalid use of auto
when deducing return type of base class template
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hello at josephloser dot com
Target Milestone: ---
The following code used to work in GCC 11.3.0, but fails on GCC 12.1.0 and
trunk.
```
#include <string_view>
constexpr auto g(auto name_fn) {
return name_fn();
}
template <char... Cs> struct ct_string {
static constexpr char str[] = {Cs..., 0};
static constexpr auto name() { return std::string_view{str, sizeof...(Cs)};
}
};
struct S : ct_string<'f', 'o', 'o'> {
constexpr auto f() {
return g(name);
}
};
int main() {
{
S s;
[[maybe_unused]] constexpr auto name = s.f();
}
return 0;
}
```
This code works on GCC 11.3.0 but fails on GCC 12.1.0 onward, including trunk.
See it live at https://godbolt.org/z/9c8vb1eP5
One workaround is to explicitly provide the return type for `ct_string::foo`
static function such as at https://godbolt.org/z/ccqPxoM5P which works on GCC
11.3.0, 12.1.0, and trunk.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/105623] [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template
2022-05-16 21:35 [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template hello at josephloser dot com
@ 2022-05-16 21:42 ` mpolacek at gcc dot gnu.org
2022-05-16 22:05 ` mpolacek at gcc dot gnu.org
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2022-05-16 21:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |12.2
Status|UNCONFIRMED |NEW
Last reconfirmed| |2022-05-16
Priority|P3 |P2
Keywords| |rejects-valid
CC| |jason at gcc dot gnu.org,
| |mpolacek at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Seems to have started with r12-1273-g1a98f830332e5a
I'll try to reduce.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/105623] [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template
2022-05-16 21:35 [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template hello at josephloser dot com
2022-05-16 21:42 ` [Bug c++/105623] " mpolacek at gcc dot gnu.org
@ 2022-05-16 22:05 ` mpolacek at gcc dot gnu.org
2022-05-16 22:23 ` davidfromonline at gmail dot com
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2022-05-16 22:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623
--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
// PR c++/105623
auto g(auto) {}
template <int...> struct ct_string {
static auto name() {}
};
struct S : ct_string<> {
auto f() { g(name); }
};
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/105623] [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template
2022-05-16 21:35 [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template hello at josephloser dot com
2022-05-16 21:42 ` [Bug c++/105623] " mpolacek at gcc dot gnu.org
2022-05-16 22:05 ` mpolacek at gcc dot gnu.org
@ 2022-05-16 22:23 ` davidfromonline at gmail dot com
2022-05-24 20:10 ` jason at gcc dot gnu.org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: davidfromonline at gmail dot com @ 2022-05-16 22:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623
--- Comment #3 from David Stone <davidfromonline at gmail dot com> ---
Simplified reproduction:
```
auto g(auto fn) {
return fn();
}
template<typename>
struct base {
static auto value() {
return 0;
}
};
struct S : base<void> {
static auto f() -> int {
return g(value);
}
};
```
See it live: https://godbolt.org/z/18n8M8oG9
An additional workaround is to explicitly take the address of the function in
line 14 of my reproducer: `return g(&value);`.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/105623] [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template
2022-05-16 21:35 [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template hello at josephloser dot com
` (2 preceding siblings ...)
2022-05-16 22:23 ` davidfromonline at gmail dot com
@ 2022-05-24 20:10 ` jason at gcc dot gnu.org
2022-05-25 15:09 ` cvs-commit at gcc dot gnu.org
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: jason at gcc dot gnu.org @ 2022-05-24 20:10 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |jason at gcc dot gnu.org
Status|NEW |ASSIGNED
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/105623] [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template
2022-05-16 21:35 [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template hello at josephloser dot com
` (3 preceding siblings ...)
2022-05-24 20:10 ` jason at gcc dot gnu.org
@ 2022-05-25 15:09 ` cvs-commit at gcc dot gnu.org
2022-05-25 17:08 ` jason at gcc dot gnu.org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-05-25 15:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:
https://gcc.gnu.org/g:850a9ce8bcca59c7efabcdeeca14c5bd905e8363
commit r13-768-g850a9ce8bcca59c7efabcdeeca14c5bd905e8363
Author: Jason Merrill <jason@redhat.com>
Date: Tue May 24 17:37:58 2022 -0400
c++: deduction from auto fn [PR105623]
Since my patch for PR90451, we defer mark_used of single functions as late
as possible. And since my r12-1273, we keep BASELINK from lookup around
rather than reconstruct it later. These both made us try to instantiate g
with a function type that still had 'auto' as its return type.
PR c++/105623
gcc/cp/ChangeLog:
* decl2.cc (mark_used): Copy type from fn to BASELINK.
* pt.cc (unify_one_argument): Call mark_single_function.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/auto-fn62.C: New test.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/105623] [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template
2022-05-16 21:35 [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template hello at josephloser dot com
` (4 preceding siblings ...)
2022-05-25 15:09 ` cvs-commit at gcc dot gnu.org
@ 2022-05-25 17:08 ` jason at gcc dot gnu.org
2022-05-31 19:31 ` cvs-commit at gcc dot gnu.org
2022-05-31 19:32 ` jason at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: jason at gcc dot gnu.org @ 2022-05-25 17:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |j-l.wynen at hotmail dot de
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
*** Bug 105716 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/105623] [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template
2022-05-16 21:35 [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template hello at josephloser dot com
` (5 preceding siblings ...)
2022-05-25 17:08 ` jason at gcc dot gnu.org
@ 2022-05-31 19:31 ` cvs-commit at gcc dot gnu.org
2022-05-31 19:32 ` jason at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-05-31 19:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:
https://gcc.gnu.org/g:d90576952356735a2152c318ef1d60221b958b15
commit r12-8441-gd90576952356735a2152c318ef1d60221b958b15
Author: Jason Merrill <jason@redhat.com>
Date: Tue May 24 17:37:58 2022 -0400
c++: deduction from auto fn [PR105623]
Since my patch for PR90451, we defer mark_used of single functions as late
as possible. And since my r12-1273, we keep BASELINK from lookup around
rather than reconstruct it later. These both made us try to instantiate g
with a function type that still had 'auto' as its return type.
PR c++/105623
gcc/cp/ChangeLog:
* decl2.cc (mark_used): Copy type from fn to BASELINK.
* pt.cc (unify_one_argument): Call mark_single_function.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/auto-fn62.C: New test.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug c++/105623] [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template
2022-05-16 21:35 [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template hello at josephloser dot com
` (6 preceding siblings ...)
2022-05-31 19:31 ` cvs-commit at gcc dot gnu.org
@ 2022-05-31 19:32 ` jason at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: jason at gcc dot gnu.org @ 2022-05-31 19:32 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105623
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 12.2/13.
^ permalink raw reply [flat|nested] 9+ messages in thread
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2022-05-16 21:35 [Bug c++/105623] New: [12/13 regression][rejects valid] invalid use of auto when deducing return type of base class template hello at josephloser dot com
2022-05-16 21:42 ` [Bug c++/105623] " mpolacek at gcc dot gnu.org
2022-05-16 22:05 ` mpolacek at gcc dot gnu.org
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