add CvSTASH_set() macro and make CvSTASH() rvalue only

Now that CvSTASH requires backreference bookkeeping, stop people from
directly assigning to it (by using CvSTASH() as an lvalue), and instead
force them to use CvSTASH_set().

1 files changed, 17 insertions, 8 deletions

diff --git a/gv.c b/gv.c
index 6d55245ae8..ab431777ee 100644
--- a/gv.c
+++ b/gv.c
@@ -235,6 +235,21 @@ Perl_cvgv_set(pTHX_ CV* cv, GV* gv)
     }
 }
 
+/* Assign CvSTASH(cv) = st, handling weak references. */
+
+void
+Perl_cvstash_set(pTHX_ CV *cv, HV *st)
+{
+    HV *oldst = CvSTASH(cv);
+    PERL_ARGS_ASSERT_CVSTASH_SET;
+    if (oldst == st)
+	return;
+    if (oldst)
+	sv_del_backref(MUTABLE_SV(oldst), MUTABLE_SV(cv));
+    SvANY(cv)->xcv_stash = st;
+    if (st)
+	Perl_sv_add_backref(aTHX_ MUTABLE_SV(st), MUTABLE_SV(cv));
+}
 
 void
 Perl_gv_init(pTHX_ GV *gv, HV *stash, const char *name, STRLEN len, int multi)
@@ -320,9 +335,7 @@ Perl_gv_init(pTHX_ GV *gv, HV *stash, const char *name, STRLEN len, int multi)
         mro_method_changed_in(GvSTASH(gv)); /* sub Foo::bar($) { (shift) } sub ASDF::baz($); *ASDF::baz = \&Foo::bar */
 	CvGV_set(cv, gv);
 	CvFILE_set_from_cop(cv, PL_curcop);
-	CvSTASH(cv) = PL_curstash;
-	if (PL_curstash)
-	    Perl_sv_add_backref(aTHX_ MUTABLE_SV(PL_curstash), MUTABLE_SV(cv));
+	CvSTASH_set(cv, PL_curstash);
 	if (proto) {
 	    sv_usepvn_flags(MUTABLE_SV(cv), proto, protolen,
 			    SV_HAS_TRAILING_NUL);
@@ -795,11 +808,7 @@ Perl_gv_autoload4(pTHX_ HV *stash, const char *name, STRLEN len, I32 method)
          * and split that value on the last '::',
          * pass along the same data via some unused fields in the CV
          */
-	if (CvSTASH(cv))
-	    sv_del_backref(MUTABLE_SV(CvSTASH(cv)), MUTABLE_SV(cv));
-        CvSTASH(cv) = stash;
-	if (stash)
-	    Perl_sv_add_backref(aTHX_ MUTABLE_SV(stash), MUTABLE_SV(cv));
+	CvSTASH_set(cv, stash);
         SvPV_set(cv, (char *)name); /* cast to lose constness warning */
         SvCUR_set(cv, len);
         return gv;