Stop lvalue subs from copying read-only scalars

They were only doing so in reference context (subroutine args,
for(...)).

Explicit return already worked, but only because I didn’t write it
well.  I’m in the process of trying to merge the two.

2 files changed, 13 insertions, 4 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 526adb88b9..f1c4977cd2 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -2693,9 +2693,7 @@ PP(pp_leavesublv)
 	    for (mark = newsp + 1; mark <= SP; mark++) {
 		if (SvTEMP(*mark))
 		    NOOP;
-		else if (SvFLAGS(*mark) & SVs_PADTMP
-		      || (SvFLAGS(*mark) & (SVf_READONLY|SVf_FAKE))
-		           == SVf_READONLY)
+		else if (SvFLAGS(*mark) & SVs_PADTMP)
 		    *mark = sv_mortalcopy(*mark);
 		else {
 		    /* Can be a localized value subject to deletion. */
diff --git a/t/op/sub_lval.t b/t/op/sub_lval.t
index 321f5461f2..e4518ffbc9 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=>156;
+plan tests=>158;
 
 sub a : lvalue { my $a = 34; ${\(bless \$a)} }  # Return a temporary
 sub b : lvalue { ${\shift} }
@@ -802,3 +802,14 @@ for my $sub (
     is +(&$sub)[0], 72, "sub returning pad var in list context$suffix";
 }
 continue { $suffix = ' (explicit return)' }
+
+# Returning read-only values in reference context
+$suffix = '';
+for (
+         sub :lvalue { $] }->(),
+         sub :lvalue { return $] }->()
+) {
+    is \$_, \$], 'read-only values are returned in reference context'
+	         .$suffix             # (they used to be copied)
+}
+continue { $suffix = ' (explicit return)' }