add new API function sv_get_backrefs()

This encapsulates the logic to extract the backrefs from a weak-referent.

Since sv_get_backrefs() can be used for a similar purposes as hv_backreferences_p()
we no longer need to export the later, and therefore this patch also reverts
ad2f46a793b4ade67d45ac0086ae62f6756c2752.

See perl #123473 for related discussion, and https://github.com/Sereal/Sereal/issues/73
for a practical example of why this API is required.

1 files changed, 6 insertions, 0 deletions

diff --git a/proto.h b/proto.h
index ce86fcabcf..c27e50b90b 100644
--- a/proto.h
+++ b/proto.h
@@ -4379,6 +4379,12 @@ PERL_CALLCONV void	Perl_sv_free2(pTHX_ SV *const sv, const U32 refcnt)
 	assert(sv)
 
 PERL_CALLCONV void	Perl_sv_free_arenas(pTHX);
+PERL_CALLCONV SV*	Perl_sv_get_backrefs(pTHX_ SV *const sv)
+			__attribute__pure__
+			__attribute__nonnull__(pTHX_1);
+#define PERL_ARGS_ASSERT_SV_GET_BACKREFS	\
+	assert(sv)
+
 PERL_CALLCONV char*	Perl_sv_gets(pTHX_ SV *const sv, PerlIO *const fp, I32 append)
 			__attribute__nonnull__(pTHX_1)
 			__attribute__nonnull__(pTHX_2);