https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91907
Bug ID: 91907
Summary: ['17] Constexpr of member function pointer as template
parameter results in inconsistent diagnostics
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: kholopov96 at gmail dot com
Target Milestone: ---
Created attachment 46945
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46945&action=edit
Preprocessed sample
Consider the following code:
----------------------------------
struct X {
template<typename F, F Method, typename ... Args>
auto Decorator(Args&&...args) {
// std::cout << "decorator\n";
(this->*Method)(&args...);
}
void bar() {
constexpr auto m_ptr = &X::barImpl;
Decorator<decltype(m_ptr), m_ptr>();
}
void barImpl() {
// std::cout << "bar\n";
}
};
----------------------------------
The compilation of this code results in inconsistent diagnostics - it literally
states the failure of converting the type to the exactly same type:
MVP.cpp:10:39: error: no matching function for call to ‘X::Decorator<void (X::*
const)(), m_ptr>()’
10 | Decorator<decltype(m_ptr), m_ptr>();
| ^
MVP.cpp:3:8: note: candidate: ‘template<class F, F Method, class ... Args> auto
X::Decorator(Args&& ...)’
3 | auto Decorator(Args&&...args) {
| ^~~~~~~~~
MVP.cpp:3:8: note: template argument deduction/substitution failed:
MVP.cpp:10:39: error: could not convert template argument ‘m_ptr’ from ‘void
(X::* const)()’ to ‘void (X::* const)()’
10 | Decorator<decltype(m_ptr), m_ptr>();
|
Other compilers, for. ex. clang++, compile this code without any issues. This
might be the copy of https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83596, but
the diagnostics is even more confusing.
Build and tested on Arch Linux, the commit url:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=6ccf1ce78e880c4b5c644d57fc86b991268c333a
Full output:
$ ~/Build/install/bin/g++ -v -save-temps -c -Wall -Wextra -std=c++17 MVP.cpp
Using built-in specs.
COLLECT_GCC=/home/igor/Build/install/bin/g++
Target: x86_64-pc-linux-gnu
Configured with: ./configure --enable-languages=c++
--prefix=/home/igor/Build/install
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.0.0 20190924 (experimental) (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-Wall' '-Wextra' '-std=c++17'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
/home/igor/Build/install/libexec/gcc/x86_64-pc-linux-gnu/10.0.0/cc1plus -E
-quiet -v -D_GNU_SOURCE MVP.cpp -mtune=generic -march=x86-64 -std=c++17 -Wall
-Wextra -fpch-preprocess -o MVP.ii
ignoring nonexistent directory
"/home/igor/Build/install/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/home/igor/Build/install/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0
/home/igor/Build/install/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/x86_64-pc-linux-gnu
/home/igor/Build/install/lib/gcc/x86_64-pc-linux-gnu/10.0.0/../../../../include/c++/10.0.0/backward
/home/igor/Build/install/lib/gcc/x86_64-pc-linux-gnu/10.0.0/include
/usr/local/include
/home/igor/Build/install/include
/home/igor/Build/install/lib/gcc/x86_64-pc-linux-gnu/10.0.0/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-Wall' '-Wextra' '-std=c++17'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
/home/igor/Build/install/libexec/gcc/x86_64-pc-linux-gnu/10.0.0/cc1plus
-fpreprocessed MVP.ii -quiet -dumpbase MVP.cpp -mtune=generic -march=x86-64
-auxbase MVP -Wall -Wextra -std=c++17 -version -o MVP.s
GNU C++17 (GCC) version 10.0.0 20190924 (experimental) (x86_64-pc-linux-gnu)
compiled by GNU C version 10.0.0 20190924 (experimental), GMP version 6.1.2,
MPFR version 4.0.2, MPC version 1.1.0, isl version none
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
GNU C++17 (GCC) version 10.0.0 20190924 (experimental) (x86_64-pc-linux-gnu)
compiled by GNU C version 10.0.0 20190924 (experimental), GMP version 6.1.2,
MPFR version 4.0.2, MPC version 1.1.0, isl version none
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: 527e25ed88abb5131b562d34bbfe759e
MVP.cpp: In member function ‘void X::bar()’:
MVP.cpp:10:39: error: no matching function for call to ‘X::Decorator<void (X::*
const)(), m_ptr>()’
10 | Decorator<decltype(m_ptr), m_ptr>();
| ^
MVP.cpp:3:8: note: candidate: ‘template<class F, F Method, class ... Args> auto
X::Decorator(Args&& ...)’
3 | auto Decorator(Args&&...args) {
| ^~~~~~~~~
MVP.cpp:3:8: note: template argument deduction/substitution failed:
MVP.cpp:10:39: error: could not convert template argument ‘m_ptr’ from ‘void
(X::* const)()’ to ‘void (X::* const)()’
10 | Decorator<decltype(m_ptr), m_ptr>();
|
