Ignore a lvalue attribute after the subroutine has been defined, and warn about it. Fixes part of [perl #68758].

1 files changed, 3 insertions, 1 deletions

diff --git a/op.c b/op.c
index 88a31d33fa..db17d142f1 100644
--- a/op.c
+++ b/op.c
@@ -5714,7 +5714,9 @@ Perl_newATTRSUB(pTHX_ I32 floor, OP *o, OP *proto, OP *attrs, OP *block)
 		 )&& !attrs) {
 		if (CvFLAGS(PL_compcv)) {
 		    /* might have had built-in attrs applied */
-		    CvFLAGS(cv) |= (CvFLAGS(PL_compcv) & CVf_BUILTIN_ATTRS);
+		    if (CvLVALUE(PL_compcv) && ! CvLVALUE(cv))
+			Perl_warner(aTHX_ packWARN(WARN_MISC), "lvalue attribute ignored after the subroutine has been defined");
+		    CvFLAGS(cv) |= (CvFLAGS(PL_compcv) & CVf_BUILTIN_ATTRS & ~CVf_LVALUE);
 		}
 		/* just a "sub foo;" when &foo is already defined */
 		SAVEFREESV(PL_compcv);