‘Attempt to bless into a ref’ with stale method caches

As of v5.16.0-81-g234df27, SvAMAGIC has only meant potentially over-
loaded.  When method changes occur, the flag is turned on.  When over-
loading tables are calculated (the first time overloading is used),
the flag is turned off if it turns out there is no overloading.

At the time I did that, I assumed that all uses of SvAMAGIC were to
avoid the inefficient code path for non-overloaded objects.  What I
did not notice at the time was that SvAMAGIC is used in pp_bless to
determine whether an object used as a class name should be exempt from
‘Attempt to bless into a reference’.

Hence, the bizarre result:

$ ./perl -Ilib -e 'sub foo{} bless [], bless []'
$ ./perl -Ilib -e 'bless [], bless []'
Attempt to bless into a reference at -e line 1.

This commit makes both die consistently, as they did in 5.16.

1 files changed, 11 insertions, 2 deletions

diff --git a/pp.c b/pp.c
index f899a3f809..d090069cd0 100644
--- a/pp.c
+++ b/pp.c
@@ -617,9 +617,18 @@ PP(pp_bless)
 
 	if (!ssv) goto curstash;
 	SvGETMAGIC(ssv);
-	if (!SvAMAGIC(ssv) && SvROK(ssv))
+	if (SvROK(ssv)) {
+	  if (!SvAMAGIC(ssv)) {
+	   frog:
 	    Perl_croak(aTHX_ "Attempt to bless into a reference");
-	ptr = SvPV_nomg_const(ssv,len);
+	  }
+	  /* SvAMAGIC is on here, but it only means potentially overloaded,
+	     so after stringification: */
+	  ptr = SvPV_nomg_const(ssv,len);
+	  /* We need to check the flag again: */
+	  if (!SvAMAGIC(ssv)) goto frog;
+	}
+	else ptr = SvPV_nomg_const(ssv,len);
 	if (len == 0)
 	    Perl_ck_warner(aTHX_ packWARN(WARN_MISC),
 			   "Explicit blessing to '' (assuming package main)");