https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80737
Tim Shen <timshen at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |timshen at gcc dot gnu.org --- Comment #2 from Tim Shen <timshen at gcc dot gnu.org> --- I reduced the test case a bit, noticing that a seemingly trivial change to <any> makes it compile. Here it is: https://godbolt.org/g/tQowts Defining the macro BUG reproduces the compile failure, however the code in BUG should have the same meaning as the other branch - it merely uses a type alias. FWIW clang 5.0.0 compiles the pre-processed code with/without -DBUG. I believe that it's a GCC frontend issue.