https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107255
Bug ID: 107255 Summary: ation and definition of a template function which vary in use of concept auto syntax are interpreted as ambiguous overloadsdeclar Product: gcc Version: 12.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: enolan at alumni dot cmu.edu Target Milestone: --- This is a rejects-valid bug where GCC has trouble determining that a declaration and definition which vary only in their use of concept auto syntax are for the same function and not multiple ambiguous overloads. Compiler explorer link: https://godbolt.org/z/4Tjcz49d9 Minimal reproduction: template <typename T> concept Foo = true; void bar(Foo auto); template <Foo F> void bar(F) {} void baz() { bar(0); } > 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++ -std=c++20 poc.cpp > the compiler output poc.cpp: In function ‘void baz()’: poc.cpp:10:8: error: call of overloaded ‘bar(int)’ is ambiguous 10 | bar(0); | ~~~^~~ poc.cpp:4:6: note: candidate: ‘void bar(auto:1) [with auto:1 = int]’ 4 | void bar(Foo auto); | ^~~ poc.cpp:7:6: note: candidate: ‘void bar(F) [with F = int]’ 7 | void bar(F) {} | ^~~