[Bug c++/16564] g++ seems to go into an infinite loop after errors

["manu at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16564

--- Comment #19 from Manuel LÃpez-IbÃÃez <manu at gcc dot gnu.org> ---
(In reply to Volker Reichelt from comment #18)
> The first error message about exceeding the maximum template instantiation
> depth appears rather quickly. So maybe we could make the first error message
> a fatal one to avoid further processing of potentially bogus nested classes.

It seems to me GCC is doing something strange. See comment #14. But what you
suggest seems to be what Clang++ is doing:

$ /usr/bin/time clang++ test.cc
test.cc:3:8: fatal error: recursive template instantiation exceeded maximum
depth of 256
  A<A> a;
       ^
test.cc:3:8: note: in instantiation of template class
      '...' requested here
  A<A> a;
       ^
test.cc:3:8: note: in instantiation of template class
      '...' requested here
  A<A> a;
       ^
test.cc:3:8: note: in instantiation of template class
      '...' requested here
  A<A> a;
       ^
test.cc:3:8: note: in instantiation of template class
      '...' requested here
  A<A> a;
       ^
test.cc:3:8: note: in instantiation of template class
      '...' requested here
  A<A> a;
       ^
test.cc:3:8: note: (skipping 247 contexts in backtrace; use
-ftemplate-backtrace-limit=0 to see all)
test.cc:3:8: note: in instantiation of template class 'A<A<A<A<A<int> > > > >'
requested here
  A<A> a;
       ^
test.cc:3:8: note: in instantiation of template class 'A<A<A<A<int> > > >'
requested here
  A<A> a;
       ^
test.cc:3:8: note: in instantiation of template class 'A<A<A<int> > >'
requested here
  A<A> a;
       ^
test.cc:3:8: note: in instantiation of template class 'A<A<int> >' requested
here
  A<A> a;
       ^
test.cc:7:8: note: in instantiation of template class 'A<int>' requested here
A<int> a;
       ^
test.cc:3:8: note: use -ftemplate-depth=N to increase recursive template
instantiation depth
  A<A> a;
       ^
1 error generated.
Command exited with non-zero status 1
0.11user 0.02system 0:00.14elapsed 96%CPU (0avgtext+0avgdata 67904maxresident)k
0inputs+0outputs (0major+6524minor)pagefaults 0swaps

And GCC's output in recent versions would look better than this because it has
automatic recursion detection:

test.cc:3:8: error: template instantiation depth exceeds maximum of 900 (use
-ftemplate-depth= to increase the maximum) instantiating âstruct ...â
   A<A> a;
        ^
test.cc:3:8:   recursively required from âstruct A<A<int> >â
test.cc:3:8:   required from âstruct A<int>â
test.cc:7:8:   required from here