[Bug preprocessor/79465] New: infinite #include cycle is not detected

[valsiterb at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79465

            Bug ID: 79465
           Summary: infinite #include cycle is not detected
           Product: gcc
           Version: 6.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: valsiterb at gmail dot com
  Target Milestone: ---

I was working on a 20 years old codebase and in order to increase compilation
speed, I've converted all header guards to #ifdef ... #error to go on and
change things around, but there was a cycle somewhere in the headers (a.h
includes b.h but b.h also includes a.h) cpp does not detect this case and goes
on unil it gets killed.
I don't know if cycle detection is even supposed to part of the preprocessor,
but I expected that #error would make it stop there. I know that there is
-Wfatal-errors directive. Shouldn't #error be be fatal or am I missing
something?