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* [Bug c++/107889] New: Incorrect parsing of qualified friend function returning decltype(auto)
@ 2022-11-27 19:47 gcc at nospam dot scs.stanford.edu
2022-11-28 6:52 ` [Bug c++/107889] " marxin at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: gcc at nospam dot scs.stanford.edu @ 2022-11-27 19:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107889
Bug ID: 107889
Summary: Incorrect parsing of qualified friend function
returning decltype(auto)
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc at nospam dot scs.stanford.edu
Target Milestone: ---
G++ 12.2.0 rejects a valid friend declaration for a fully-qualified function
returning `decltype(auto)`. To reproduce the problem, you can try to compile
the following code with `g++ -std=c++20 -c bug.cc`:
decltype(auto)
f()
{
}
struct S {
friend decltype(auto) ::f();
};
This results in the following error:
$ c++ -std=c++20 -c bug.cc
bug.cc:7:27: error: 'decltype(auto)' is not a class type
7 | friend decltype(auto) ::f();
| ^
bug.cc:7:27: error: 'decltype(auto)' is not a class type
bug.cc:7:27: error: 'decltype(auto)' is not a class type
bug.cc:7:29: error: 'decltype(auto)' is not a class type
7 | friend decltype(auto) ::f();
| ^
bug.cc:7:10: error: ISO C++ forbids declaration of 'f' with no type
[-fpermissive]
7 | friend decltype(auto) ::f();
| ^~~~~~~~~~~~~~
bug.cc:7:29: error: invalid use of 'decltype(auto)'
7 | friend decltype(auto) ::f();
A similar problem was reported in bug #59766 for friend functions returning
auto. It seems to have been mostly fixed, but the combination of
decltype(auto) and the function name being qualified (::f) is still a problem.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/107889] Incorrect parsing of qualified friend function returning decltype(auto)
2022-11-27 19:47 [Bug c++/107889] New: Incorrect parsing of qualified friend function returning decltype(auto) gcc at nospam dot scs.stanford.edu
@ 2022-11-28 6:52 ` marxin at gcc dot gnu.org
2022-11-28 9:24 ` redi at gcc dot gnu.org
2022-11-28 9:28 ` redi at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: marxin at gcc dot gnu.org @ 2022-11-28 6:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107889
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2022-11-28
CC| |marxin at gcc dot gnu.org
--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Clang accepts the code.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/107889] Incorrect parsing of qualified friend function returning decltype(auto)
2022-11-27 19:47 [Bug c++/107889] New: Incorrect parsing of qualified friend function returning decltype(auto) gcc at nospam dot scs.stanford.edu
2022-11-28 6:52 ` [Bug c++/107889] " marxin at gcc dot gnu.org
@ 2022-11-28 9:24 ` redi at gcc dot gnu.org
2022-11-28 9:28 ` redi at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: redi at gcc dot gnu.org @ 2022-11-28 9:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107889
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think this is https://wg21.link/cwg1828 which was resolved by
https://wg21.link/p1787 which GCC does not implement yet.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/107889] Incorrect parsing of qualified friend function returning decltype(auto)
2022-11-27 19:47 [Bug c++/107889] New: Incorrect parsing of qualified friend function returning decltype(auto) gcc at nospam dot scs.stanford.edu
2022-11-28 6:52 ` [Bug c++/107889] " marxin at gcc dot gnu.org
2022-11-28 9:24 ` redi at gcc dot gnu.org
@ 2022-11-28 9:28 ` redi at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: redi at gcc dot gnu.org @ 2022-11-28 9:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107889
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to David Mazières from comment #0)
> A similar problem was reported in bug #59766 for friend functions returning
> auto.
That's unrelated.
The problem here is that decltype(auto)::f is a nested-name-specifier for a
member 'f' so is parsed as part of the return type, not the function name. This
is what C++20 (and all earlier standards) said. The ambiguity has been resolved
as a DR against earlier standards, but GCC doesn't implement that change yet,
as shown at https://gcc.gnu.org/projects/cxx-status.html#cxx23
^ permalink raw reply [flat|nested] 4+ messages in thread
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2022-11-27 19:47 [Bug c++/107889] New: Incorrect parsing of qualified friend function returning decltype(auto) gcc at nospam dot scs.stanford.edu
2022-11-28 6:52 ` [Bug c++/107889] " marxin at gcc dot gnu.org
2022-11-28 9:24 ` redi at gcc dot gnu.org
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