WIP initial hack at fixing GH#22121 by storing PL_prevailing_version …

…in the frozen hinthash stored by ck_entereval()

op.c

@@ -12416,6 +12416,8 @@ Perl_ck_eval(pTHX_ OP *o)
     PERL_ARGS_ASSERT_CK_EVAL;
 
     PL_hints |= HINT_BLOCK_SCOPE;
+    if(PL_prevailing_version != 0)
+        PL_hints |= HINT_LOCALIZE_HH;
     if (o->op_flags & OPf_KIDS) {
         SVOP * const kid = cSVOPx(cUNOPo->op_first);
         assert(kid);
@@ -12457,6 +12459,7 @@ Perl_ck_eval(pTHX_ OP *o)
      && !(o->op_private & OPpEVAL_COPHH) && GvHV(PL_hintgv)) {
         /* Store a copy of %^H that pp_entereval can pick up. */
         HV *hh = hv_copy_hints_hv(GvHV(PL_hintgv));
+        hv_stores(hh, "CORE/prevailing_version", newSVuv(PL_prevailing_version));
         OP *hhop;
         hhop = newSVOP(OP_HINTSEVAL, 0, MUTABLE_SV(hh));
         /* append hhop to only child  */

pp_ctl.c

@@ -4062,6 +4062,7 @@ S_doeval_compile(pTHX_ U8 gimme, CV* outside, U32 seq, HV *hh)
     else {
         PL_hints = saveop->op_private & OPpEVAL_COPHH
                      ? oldcurcop->cop_hints : (U32)saveop->op_targ;
+        PL_prevailing_version = 0; /* we might change this below */
 
         /* making 'use re eval' not be in scope when compiling the
          * qr/mabye_has_runtime_code_block/ ensures that we don't get
@@ -4076,6 +4077,12 @@ S_doeval_compile(pTHX_ U8 gimme, CV* outside, U32 seq, HV *hh)
             SvREFCNT_dec(GvHV(PL_hintgv));
             GvHV(PL_hintgv) = hh;
             FETCHFEATUREBITSHH(hh);
+            SV *versv;
+            /* hh is a new copy for us to use; we are permitted to delete keys */
+            if((versv = hv_deletes(hh, "CORE/prevailing_version", 0)) && SvOK(versv)) {
+                SAVEI16(PL_prevailing_version);
+                PL_prevailing_version = SvUV(versv);
+            }
         }
     }
     SAVECOMPILEWARNINGS();