Initial hack at restoring iter var value after refaliased foreach

Author: leonerd

inline.h

@@ -4152,6 +4152,48 @@ Perl_cx_poploop(pTHX_ PERL_CONTEXT *cx)
         cx->blk_loop.itersave = NULL;
         SvREFCNT_dec(cursv);
     }
+    if (cx->cx_type & CXp_FOR_LVREF) {
+        SV *itervar = (SV *)(cx)->blk_loop.itervar_u.gv;
+        SV *origval = (cx)->blk_loop.itersave;
+        assert(SvTYPE(itervar) == SVt_PVMG);
+        MAGIC *mg = SvMAGIC(itervar);
+        assert(mg);
+        assert(mg->mg_type == PERL_MAGIC_lvref);
+        if (!mg->mg_obj) {
+            // LV ref around a lexical, mg_len gives its pad index
+            SV **padslot = &PAD_SVl(mg->mg_len);
+            SV *oldsv = *padslot;
+            *padslot = origval;
+            SvREFCNT_dec(oldsv);
+        }
+        else {
+            // LV ref around a package lexical, mg_obj gives its GV
+            GV *gv = (GV *)mg->mg_obj;
+            SV *oldsv;
+            switch(mg->mg_private & OPpLVREF_TYPE) {
+                case OPpLVREF_SV:
+                    oldsv = GvSVn(gv);
+                    GvSVn(gv) = origval;
+                    break;
+
+                case OPpLVREF_AV:
+                    oldsv = (SV *)GvAV(gv);
+                    GvAV(gv) = (AV *)origval;
+                    break;
+
+                case OPpLVREF_HV:
+                    oldsv = (SV *)GvHV(gv);
+                    GvHV(gv) = (HV *)origval;
+                    break;
+
+                case OPpLVREF_CV:
+                    oldsv = (SV *)GvCV(gv);
+                    GvCV_set(gv, (CV *)origval);
+                    break;
+            }
+            SvREFCNT_dec(oldsv);
+        }
+    }
     if (cx->cx_type & (CXp_FOR_GV|CXp_FOR_LVREF))
         SvREFCNT_dec(cx->blk_loop.itervar_u.svp);
 }

pp_ctl.c

@@ -2622,9 +2622,26 @@ PP(pp_enteriter)
         }
         else {                          /* LV ref: for \$foo (...) */
             assert(SvTYPE(sv) == SVt_PVMG);
-            assert(SvMAGIC(sv));
-            assert(SvMAGIC(sv)->mg_type == PERL_MAGIC_lvref);
             itersave = NULL;
+            MAGIC *mg = SvMAGIC(sv);
+            assert(mg);
+            assert(mg->mg_type == PERL_MAGIC_lvref);
+            if (!mg->mg_obj) {
+                // LV ref around a lexical, mg_len gives its pad index
+                itersave = SvREFCNT_inc_NN(PAD_SV(mg->mg_len));
+            }
+            else {
+                // LV ref around a package lexical, mg_obj gives its GV
+                GV *gv = (GV *)mg->mg_obj;
+                assert(SvTYPE(gv) == SVt_PVGV);
+                switch(mg->mg_private & OPpLVREF_TYPE) {
+                    case OPpLVREF_SV: itersave =       GvSVn(gv); break;
+                    case OPpLVREF_AV: itersave = (SV *)GvAV(gv);  break;
+                    case OPpLVREF_HV: itersave = (SV *)GvHV(gv);  break;
+                    case OPpLVREF_CV: itersave = (SV *)GvCV(gv);  break;
+                }
+                SvREFCNT_inc_void(itersave);
+            }
             cxflags = CXp_FOR_LVREF;
         }
         /* we transfer ownership of 1 ref count of itervarp from the stack

t/op/decl-refs.t

@@ -4,7 +4,7 @@ BEGIN {
     set_up_inc('../lib');
 }
 
-plan 402;
+plan 408;
 
 for my $decl (qw< my CORE::state our local >) {
     for my $funny (qw< $ @ % >) {
@@ -120,3 +120,30 @@ ENE
     $code =~ s/is ?no?t/is/g if $decl eq 'our';
     eval $code or die $@;
 }}
+
+# GH#24028
+{
+    my $slexical = 42;
+    for \$slexical ( \1, \2, \3 ) { }
+    is $slexical, 42, 'scalar lexical restored after foreach-refalias';
+
+    my @alexical = (42);
+    for \@alexical ( [1], [2], [3] ) { }
+    is $alexical[0], 42, 'array lexical restored after foreach-refalias';
+
+    my %hlexical = (k => 42);
+    for \%hlexical ( {k => 1}, {k => 2}, {k => 3} ) { }
+    is $hlexical{k}, 42, 'hash lexical restored after foreach-refalias';
+
+    our $spkgvar = 84;
+    for \$spkgvar ( \1, \2, \3 ) { }
+    is $spkgvar, 84, 'scalar pkgvar restored after foreach-refalias';
+
+    our @apkgvar = (84);
+    for \@apkgvar ( [1], [2], [3] ) { }
+    is $apkgvar[0], 84, 'array pkgvar restored after foreach-refalias';
+
+    our %hpkgvar = (k => 84);
+    for \%hpkgvar ( {k => 1}, {k => 2}, {k => 3} ) { }
+    is $hpkgvar{k}, 84, 'hash pkgvar restored after foreach-refalias';
+}