https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85846
Bug ID: 85846 Summary: [Concepts] Concept as value in initializer: bogus declared-as-implicit-template error Product: gcc Version: 9.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: hstong at ca dot ibm.com Target Milestone: --- When a concept with a non-type prototype parameter is used as a variable template in a context where the most vexing parse would prefer interpretation of an ambiguous construct as naming a type, GCC produces a bogus message about creating an implicit non-function template. In the case below, either f is being declared as a function, or Foo<> cannot be considered a type (and therefore, it cannot cause formation of an implicit template through the abbreviated function template mechanism). ### SOURCE (<stdin>): template <int = 0> concept bool Foo = true; bool f(Foo<>); ### COMPILER INVOCATION: g++ -fsyntax-only -xc++ -fconcepts - ### ACTUAL OUTPUT: <stdin>:2:6: error: non-function 'f' declared as implicit template ### EXPECTED OUTPUT: (Clean compile). ### COMPILER VERSION INFO (g++ -v): Using built-in specs. COLLECT_GCC=/opt/wandbox/gcc-head/bin/g++ COLLECT_LTO_WRAPPER=/opt/wandbox/gcc-head/libexec/gcc/x86_64-pc-linux-gnu/9.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../source/configure --prefix=/opt/wandbox/gcc-head --enable-languages=c,c++ --disable-multilib --without-ppl --without-cloog-ppl --enable-checking=release --disable-nls --enable-lto LDFLAGS=-Wl,-rpath,/opt/wandbox/gcc-head/lib,-rpath,/opt/wandbox/gcc-head/lib64,-rpath,/opt/wandbox/gcc-head/lib32 Thread model: posix gcc version 9.0.0 20180518 (experimental) (GCC)