https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91023
Bug ID: 91023
Summary: Unification Fails for parameter pack
Product: gcc
Version: 9.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: christoph.hoeger at celeraone dot com
Target Milestone: ---
Created attachment 46529
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46529&action=edit
Automatically generated preprocessed output
In the example below, the unification of the template argument fails with the
message:
➜ gcc.bug g++ --std=c++17 input.cpp
input.cpp: In substitution of 'template<class ... T>
std::optional<std::variant<_Types ...> > parse_variant(const Foo<T,
std::variant<_Types ...> >& ...) [with T = <missing>]':
input.cpp:33:43: required from here
input.cpp:33:43: internal compiler error: in tsubst, at cp/pt.c:14560
33 | const auto x = parse_variant(a(), b());
| ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://bugzilla.redhat.com/bugzilla> for instructions.
Preprocessed source stored into /tmp/cc1jpH2s.out file, please attach this to
your bugreport.
distcc[31035] ERROR: compile input.cpp on localhost failed
Example:
#include <variant>
#include <optional>
template <typename T, typename S>
struct Foo
{
};
template <typename... T>
std::optional<std::variant<T...>>
parse_variant(const Foo<T, std::variant<T...>> &... variants)
{
return {};
}
struct A {};
struct B {};
using var_test = std::variant<A, B>;
Foo<A, var_test> a()
{
return {};
}
Foo<B, var_test> b()
{
return {};
}
int main()
{
const auto x = parse_variant(a(), b());
return 0;
}
gcc version information:
➜ gcc.bug g++ -v
Using built-in specs.
COLLECT_GCC=/usr/bin/g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/9/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap
--enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,lto --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --enable-multilib
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-gnu-unique-object --enable-linker-build-id
--with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin
--enable-initfini-array --with-isl --enable-offload-targets=nvptx-none
--without-cuda-driver --enable-gnu-indirect-function --enable-cet
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 9.1.1 20190503 (Red Hat 9.1.1-1) (GCC)
