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* [Bug c++/97988] New: [C++20] Forward-declared class type declared inside requires-expression gives weird inconsistencies
@ 2020-11-25 16:20 arthur.j.odwyer at gmail dot com
2021-08-17 8:36 ` [Bug c++/97988] " pinskia at gcc dot gnu.org
2023-06-09 14:36 ` ppalka at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: arthur.j.odwyer at gmail dot com @ 2020-11-25 16:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97988
Bug ID: 97988
Summary: [C++20] Forward-declared class type declared inside
requires-expression gives weird inconsistencies
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: arthur.j.odwyer at gmail dot com
Target Milestone: ---
// https://godbolt.org/z/sxWY1f
template<class P>
concept C = requires (P ptr) { (struct D*)ptr; };
struct D {};
D d;
====
Clang accepts. GCC rejects; GCC's error messages imply that GCC is sometimes
treating `D` as a class template `template<class P> struct D` and sometimes
treating it as a normal class type, as if its internal representation is
inconsistent.
<source>:6:3: error: class template argument deduction failed:
6 | D d;
| ^
<source>:6:3: error: no matching function for call to 'D()'
<source>:3:40: note: candidate: 'template<class P> D()-> D'
3 | concept C = requires (P ptr) { (struct D*)ptr; };
| ^
<source>:3:40: note: template argument deduction/substitution failed:
<source>:6:3: note: couldn't deduce template parameter 'P'
6 | D d;
| ^
<source>:3:40: note: candidate: 'template<class P> D(D)-> D'
3 | concept C = requires (P ptr) { (struct D*)ptr; };
| ^
<source>:3:40: note: template argument deduction/substitution failed:
<source>:6:3: note: candidate expects 1 argument, 0 provided
6 | D d;
| ^
====
I can also make GCC segfault by trying to use `D` as an NTTP, but I think
that's essentially just a duplicate of #95159 #95291 #96123 #97749 etc., not
necessarily related to the rejects-invalid bug described here.
template<class P>
concept C = requires (P ptr) { (struct D*)ptr; };
struct D { constexpr D(); };
template<D d> struct S {};
S<1> s;
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2020-11-25 16:20 [Bug c++/97988] New: [C++20] Forward-declared class type declared inside requires-expression gives weird inconsistencies arthur.j.odwyer at gmail dot com
2021-08-17 8:36 ` [Bug c++/97988] " pinskia at gcc dot gnu.org
2023-06-09 14:36 ` ppalka at gcc dot gnu.org
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