https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102547
--- Comment #4 from Bob Steagall <bob.steagall.cpp at gmail dot com> --- I have applied this tentative change to line 23436 of gcc/cp/pt.c from the gcc-11.2.0 source tarball, and can confirm that the test case compiles for me. The code I was working on also compiles, links, and appears to run correctly. I don't know if this is the final fix, but it is progress.
