https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99374
Bug ID: 99374
Summary: C++17/20 mode fails to recognise pointer-to-member
functions of incomplete types in conditional
expression
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: cjdb.ns at gmail dot com
Target Milestone: ---
Created attachment 50296
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50296&action=edit
Failure with -std=c++17
GCC seems to be unable to handle pointer-to-member functions of incomplete
types in conditional expressions. The following works on both Clang and MSVC,
and some invocations of GCC.
```
struct S;
using F1 = int (S::*)();
using F2 = int (S::*)() noexcept;
auto v = true ? F1() : F2();
auto w = true ? F2() : F1();
```
This appears to work if `-std=c++14`, but not `-std=c++17` or `-std=c++20` for
GCC versions >= 7. GCC < 7 doesn't have a problem compiling even in C++17 mode.
# Versions
* All GCC releases from 7.1.0 through trunk.
# System type
* Ubuntu 18.04 (checked GCC 10.1)
* Ubuntu 20.04 on WSL2 (checked GCC 10.2)
* Debian (checked GCC 10.2.1)
* Compiler Explorer (checked all other reported versions).
# Options given to GCC
`g++ -save-temps fail-17.cpp -c -std=c++17`
# Diagnostic
```
fail-17.cpp:5:27: error: could not convert ‘((int (S::*)() noexcept)0)’ from
‘int (S::*)() noexcept’ to ‘int (S::*)()’
5 | auto v = true ? F1() : F2();
| ^
| |
| int (S::*)() noexcept
fail-17.cpp:6:27: error: could not convert ‘((int (S::*)() noexcept)0)’ from
‘int (S::*)() noexcept’ to ‘int (S::*)()’
6 | auto w = true ? F2() : F1();
| ^
| |
| int (S::*)() noexcept
```
