Reset method caches when GPs are shared

The new MRO stuff in 5.10 made PL_sub_generation++ mostly unnecessary,
and almost all uses of it were replaced with mro_method_changed_in.

There is only one problem: That doesn’t actually work properly.  After
glob-to-glob assignment (*foo = *bar), both globs share the same GP
(glob pointer, or list of glob slots).  But there is no list of GVs
associated with any GP.  So there is no way, given a GV whose GP
is shared, to find out what other classes might need their method
caches reset.

sub B::b { "b" }
*A::b = *B::b;
@C::ISA = "A";
print C->b, "\n";  # should print "b"
eval 'sub B::b { "c" }';
print C->b, "\n";  # should print "c"
__END__

$ perl5.8.9 foo
b
c
$ perl5.10.0 foo
b
b

And it continues up to 5.16.x.

If a GP is shared, then those places where mro_method_changed_in is
called after the GP has been modified must do PL_sub_generation++
instead if the GP is shared, which can be detected through its refer-
ence count.

1 files changed, 1 insertions, 1 deletions

diff --git a/scope.c b/scope.c
index cd342d05d3..8eca725f22 100644
--- a/scope.c
+++ b/scope.c
@@ -861,7 +861,7 @@ Perl_leave_scope(pTHX_ I32 base)
 	    GvGP_set(gv, (GP*)ptr);
             /* putting a method back into circulation ("local")*/
 	    if (GvCVu(gv) && (hv=GvSTASH(gv)) && HvENAME_get(hv))
-                mro_method_changed_in(hv);
+                gv_method_changed(gv);
 	    SvREFCNT_dec(gv);
 	    break;
 	case SAVEt_FREESV: