Preserve overloaded arithmetic result lifetime during ++ and --

docs/about/changelog.md

@@ -6,6 +6,7 @@ priorities and future plans.
 
 ## Work in progress
 
+- Preserve reference lifetime when overloaded `++` and `--` fall back to arithmetic (#1901).
 - Parse forward-declared qualified classes as indirect constructors inside `new` methods (#1899).
 
 - Match Perl `Encode` aliases for ANSI X3.4-1968, HZ-GB-2312, and ISO-8859-8-I, and include the BOM when encoding generic UTF-32 (#1897).

src/main/java/org/perlonjava/runtime/runtimetypes/RuntimeScalar.java

@@ -5722,8 +5722,7 @@ private RuntimeScalar preAutoIncrementWithoutWatcherNotification() {
                         result = ctx.tryOverload("(+", new RuntimeArray(this, scalarOne, scalarUndef));
                         if (result != null) {
                             // For fallback, + should NOT modify operand, so we handle assignment
-                            this.type = result.type;
-                            this.value = copyScalarPayload(result.type, result.value);
+                            set(result);
                             return this;
                         }
 
@@ -6005,8 +6004,7 @@ private RuntimeScalar postAutoIncrementLarge() {
                         result = ctx.tryOverload("(+", new RuntimeArray(this, scalarOne, scalarUndef));
                         if (result != null) {
                             // For fallback, + should NOT modify operand, so we handle assignment
-                            this.type = result.type;
-                            this.value = copyScalarPayload(result.type, result.value);
+                            set(result);
                             return old;
                         }
 
@@ -6157,8 +6155,7 @@ private RuntimeScalar preAutoDecrementWithoutWatcherNotification() {
                         result = ctx.tryOverload("(-", new RuntimeArray(this, scalarOne, scalarUndef));
                         if (result != null) {
                             // For fallback, - should NOT modify operand, so we handle assignment
-                            this.type = result.type;
-                            this.value = copyScalarPayload(result.type, result.value);
+                            set(result);
                             return this;
                         }
                     }
@@ -6316,8 +6313,7 @@ private RuntimeScalar postAutoDecrementWithoutWatcherNotification() {
                         result = ctx.tryOverload("(-", new RuntimeArray(this, scalarOne, scalarUndef));
                         if (result != null) {
                             // For fallback, - should NOT modify operand, so we handle assignment
-                            this.type = result.type;
-                            this.value = copyScalarPayload(result.type, result.value);
+                            set(result);
                             return old;
                         }
                     }

src/test/resources/unit/overload_autoincrement_preserves_result_lifetime.t

@@ -0,0 +1,48 @@
+use strict;
+use warnings;
+no warnings 'numeric';
+use Test::More;
+
+{
+    package Local::FormattedDate;
+    use Scalar::Util qw(refaddr);
+    our %FORMATS;
+
+    use overload
+        '+' => sub { _offset($_[0], $_[1]) },
+        '-' => sub { _offset($_[0], -$_[1]) },
+        '""' => sub {
+            my ($self) = @_;
+            return sprintf $FORMATS{refaddr($self)}, $$self;
+        },
+        fallback => 1;
+
+    sub _offset {
+        my ($self, $delta) = @_;
+        my $result = bless \($$self + $delta), ref($self);
+        $FORMATS{refaddr($result)} = $FORMATS{refaddr($self)};
+        return $result;
+    }
+
+    sub set_format { $FORMATS{refaddr($_[0])} = $_[1] }
+
+    sub DESTROY { delete $FORMATS{refaddr($_[0])} }
+}
+
+my $value = 20261101;
+my $date = bless \$value, 'Local::FormattedDate';
+$date->set_format('custom:%d');
+
+++ $date;
+is("$date", 'custom:20261102', 'preincrement keeps state on the overloaded result');
+
+-- $date;
+is("$date", 'custom:20261101', 'predecrement keeps state on the overloaded result');
+
+$date++;
+is("$date", 'custom:20261102', 'postincrement keeps state on the overloaded result');
+
+$date--;
+is("$date", 'custom:20261101', 'postdecrement keeps state on the overloaded result');
+
+done_testing();