Fix explicit return of pad var in list lv context

This is something that commit e08be60 missed, though it never worked
properly, even in 5.14, as explicit return from lvalue subs used to
copy return values.

As the commit message for e08be60 states, returning a scalar itself
from an lvalue sub does not work if it is a pad variable with a refer-
ence count of 1, because the sub-popping code clears it on exit.

The one code path that did not account for this was list lvalue con-
text (real lvalue context, not just potentially lvalue).  The only
observable effect this has is that assigning to a magic pad variable
returned from a subroutine in list context will not trigger set-magic.

This commit fixes it and also adds tests for returned magic pad vars
in all combinations of list/scalar lvalue/ref context.

3 files changed, 42 insertions, 2 deletions

diff --git a/pod/perldelta.pod b/pod/perldelta.pod
index 095785c629..751da25964 100644
--- a/pod/perldelta.pod
+++ b/pod/perldelta.pod
@@ -384,6 +384,9 @@ the attribute.
 
 =item *
 
+=for comment
+Not necessary for perl5160delta
+
 The remaining discrepancies between explicit and implicit return from
 lvalue subroutines have been resolved.  They mainly involved which error
 message to display when a read-only value is returned in lvalue context.
@@ -392,6 +395,16 @@ lvalue context is now forbidden for explicit return, as it always has been
 for implicit return.  This is not a regression from 5.14, as all the cases
 in which it could happen where previously syntax errors.
 
+=item *
+
+=for comment
+Not necessary for perl5160delta
+
+Explicitly returning a tied C<my> variable from an lvalue subroutine in
+list lvalue context used to clear the variable before the assignment could
+happen.  This is something that was missed when explicit return was made to
+work in 5.15.0.
+
 =back
 
 =head1 Known Problems
diff --git a/pp_ctl.c b/pp_ctl.c
index 98f2e5d2a6..36ba24a664 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -2334,7 +2334,10 @@ S_return_lvalues(pTHX_ SV **mark, SV **sp, SV **newsp, I32 gimme,
 			SvREADONLY(TOPs) ? "readonly value" : "temporary");
 	    }
 	    else
-		*++newsp = *MARK;
+		*++newsp =
+		    SvTEMP(*MARK)
+		       ? *MARK
+		       : sv_2mortal(SvREFCNT_inc_simple_NN(*MARK));
 	}
     }
     PL_stack_sp = newsp;
diff --git a/t/op/sub_lval.t b/t/op/sub_lval.t
index 06ac461417..64e7b4edcc 100644
--- a/t/op/sub_lval.t
+++ b/t/op/sub_lval.t
@@ -3,7 +3,7 @@ BEGIN {
     @INC = '../lib';
     require './test.pl';
 }
-plan tests=>167;
+plan tests=>175;
 
 sub a : lvalue { my $a = 34; ${\(bless \$a)} }  # Return a temporary
 sub b : lvalue { ${\shift} }
@@ -556,6 +556,30 @@ is($@, "", "element of tied array");
 is ($Tie_Array::val[0], "value");
 
 
+# Check that tied pad vars that are returned can be assigned to
+sub TIESCALAR { bless [] }
+sub STORE {$wheel = $_[1]}
+sub FETCH {$wheel}
+sub tied_pad_var  :lvalue { tie my $tyre, ''; $tyre }
+sub tied_pad_varr :lvalue { tie my $tyre, ''; return $tyre }
+tied_pad_var = 1;
+is $wheel, 1, 'tied pad var returned in scalar lvalue context';
+tied_pad_var->${\sub{ $_[0] = 2 }};
+is $wheel, 2, 'tied pad var returned in scalar ref context';
+(tied_pad_var) = 3;
+is $wheel, 3, 'tied pad var returned in list lvalue context';
+$_ = 4 for tied_pad_var;
+is $wheel, 4, 'tied pad var returned in list ref context';
+tied_pad_varr = 5;
+is $wheel, 5, 'tied pad var explicitly returned in scalar lvalue context';
+tied_pad_varr->${\sub{ $_[0] = 6 }};
+is $wheel, 6, 'tied pad var explicitly returned in scalar ref context';
+(tied_pad_varr) = 7;
+is $wheel, 7, 'tied pad var explicitly returned in list lvalue context';
+$_ = 8 for tied_pad_varr;
+is $wheel, 8, 'tied pad var explicitly returned in list ref context';
+
+
 # Test explicit return of lvalue expression
 {
     # subs are copies from tests 1-~18 with an explicit return added.