https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106969
Bug ID: 106969
Summary: member function constness incorrectly propagates to
local class member function return type deduction
Product: gcc
Version: 12.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: enolan at alumni dot cmu.edu
Target Milestone: ---
When using decltype in the return type of a member function of a local class
defined inside of a const member function, the type of 'this' seems to be
deduced as a pointer to const, when it should be a pointer to non-const.
Compiler explorer link: https://godbolt.org/z/9KKbrzq1e
Minimal reproduction:
struct Context
{
void
action() const
{
struct
{
int wrapped;
decltype( & wrapped ) get() { return &wrapped; }
} t;
*t.get()= 42;
}
};
Note that if the local class member function definition is changed to:
auto get() -> decltype( & wrapped ) { return &wrapped; }
Then the bug no longer appears.
> the exact version of gcc
gcc version 12.2.1 20220819 (Red Hat 12.2.1-2) (GCC)
> the system type
Fedora release 38 (Rawhide)
> the options given when GCC was configured/built
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 --enable-libstdcxx-backtrace
--with-linker-hash-style=gnu --enable-plugin --enable-initfini-array
--with-isl=/builddir/build/BUILD/gcc-12.2.1-20220819/obj-x86_64-redhat-linux/isl-install
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-offload-defaulted --enable-gnu-indirect-function --enable-cet
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
--with-build-config=bootstrap-lto --enable-link-serialization=1
> the complete command line that triggers the bug
g++ poc.cpp
> the compiler output
poc.cpp: In member function ‘void Context::action() const’:
poc.cpp:12:17: error: assignment of read-only location ‘* t.Context::action()
const::<unnamed struct>::get()’
12 | *t.get()= 42;
| ~~~~~~~~^~~~
