[perl #112708] Update overloadedness with ‘use overload’

Instead of setting a class’s overloaded (HvAMAGIC) flag when bless
happens, we should do it in ‘use overload’.  Otherwise, if a non-over-
loaded class gains overloading via ‘use overload’, existing objects
won’t get overloading until another object is blessed into the
same class.

Inherited overloading that is turned on due to @ISA changes still
won’t work yet.  That will come in a later commit.

Doing this via %OVERLOAD magic would require referencing
the stash from magic.  Since overload.pm already does
‘*{$package . "::()"} = \&nil’, triggering mro_method_changed_in,
the simplest approach is to turn on the stash’s AMAGIC flag in
mro_method_changed_in.  Since, if there is no overloading, the flag
will be turned off on the next attempted overload call (in Gv_AM in
sv.h), there should be noticeable slowdown.

I had to turn off HvAMAGIC in hv_undef, to prevent ‘Can't use anony-
nous symbol table for method lookup’ from occurring when stringifying
an object whose package has been undefined.

1 files changed, 4 insertions, 0 deletions

diff --git a/mro.c b/mro.c
index caa989db31..a8ff42ec8d 100644
--- a/mro.c
+++ b/mro.c
@@ -1346,6 +1346,10 @@ Perl_mro_method_changed_in(pTHX_ HV *stash)
                 hv_clear(mrometa->mro_nextmethod);
         }
     }
+
+    /* The method change may be due to *{$package . "::()"} = \&nil; in
+       overload.pm. */
+    HvAMAGIC_on(stash);
 }
 
 void