https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95789
Bug ID: 95789 Summary: Const method is allowed to return non-const reference on template class Product: gcc Version: 10.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: ivan at chebykin dot org Target Milestone: --- Created attachment 48762 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48762&action=edit Preprocessed file without iostream Hello, I've recently updated from gcc 9.3.0 to 10.1.0 and found some unexpected behaviour when trying to compile this code: #include <iostream> struct B { int n; }; template <typename T> struct A { B& get() const { return f; } B f; }; int main() { A<int> a; a.f = {}; a.get().n = 10; std::cout << a.f.n << std::endl; return 0; } As I understand this code shouldn't compile with error binding reference of type ‘B&’ to ‘const B’ discards qualifiers but this code compiles successfully. What is more interesting is that this code will stop compiling if I remove template or if I use POD type like int. Neither gcc 9.3.0 compiles this code nor clang does. GCC info: Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --with-isl --with-linker-hash-style=gnu --with-system-zlib --enable-__cxa_atexit --enable-cet=auto --enable-checking=release --enable-clocale=gnu --enable-default-pie --enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object --enable-install-libiberty --enable-linker-build-id --enable-lto --enable-multilib --enable-plugin --enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch --disable-libunwind-exceptions --disable-werror gdc_include_dir=/usr/include/dlang/gdc Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 10.1.0 (GCC) Compiling with -Wall -Wextra yields no output warnings or errors. I've attached preprocessed file without iostream.