test: cover by-reference return override semantics

phpunit/code/override_byref_return_abstract_dropped.php

@@ -0,0 +1,16 @@
+<?php
+
+abstract class AbstractByRefReturn
+{
+    abstract public function &value(): array;
+}
+
+class ConcreteByRefReturn extends AbstractByRefReturn
+{
+    public function value(): array
+    {
+        return [];
+    }
+}
+
+function main() {}

phpunit/code/override_byref_return_interface_dropped.php

@@ -0,0 +1,16 @@
+<?php
+
+interface ByRefReturnContract
+{
+    public function &value(): array;
+}
+
+class ByRefReturnImplementation implements ByRefReturnContract
+{
+    public function value(): array
+    {
+        return [];
+    }
+}
+
+function main() {}

phpunit/src/MethodOverrideByRefReturnTest.php

@@ -21,4 +21,22 @@ class MethodOverrideByRefReturnTest extends BaseTest
             'override_byref_return_dropped.php',
         );
     }
+
+    public function testAbstractMethodImplementationCannotDropByRefReturn(): void
+    {
+        $this->exec(
+            'Declaration of `ConcreteByRefReturn::value()` must be compatible with '
+                . '`AbstractByRefReturn::value()`',
+            'override_byref_return_abstract_dropped.php',
+        );
+    }
+
+    public function testInterfaceImplementationCannotDropByRefReturn(): void
+    {
+        $this->exec(
+            'Declaration of `ByRefReturnImplementation::value()` must be compatible with '
+                . '`ByRefReturnContract::value()`',
+            'override_byref_return_interface_dropped.php',
+        );
+    }
 }

tests/compiler/ref/abstract-interface-add-byref-return.phpt

@@ -0,0 +1,47 @@
+--TEST--
+Abstract and interface implementations may add a by-reference return
+--FILE--
+<?php
+
+abstract class AbstractValueSource
+{
+    abstract public function abstractValue(): int;
+}
+
+interface ValueSourceContract
+{
+    public function interfaceValue(): int;
+}
+
+final class ReferenceValueSource extends AbstractValueSource implements ValueSourceContract
+{
+    private int $abstractStored = 5;
+    private int $interfaceStored = 7;
+
+    public function &abstractValue(): int
+    {
+        return $this->abstractStored;
+    }
+
+    public function &interfaceValue(): int
+    {
+        return $this->interfaceStored;
+    }
+}
+
+function main(): void
+{
+    $source = new ReferenceValueSource();
+
+    $abstractAlias =& $source->abstractValue();
+    $abstractAlias = 50;
+    var_dump($source->abstractValue());
+
+    $interfaceAlias =& $source->interfaceValue();
+    $interfaceAlias = 70;
+    var_dump($source->interfaceValue());
+}
+?>
+--EXPECT--
+int(50)
+int(70)

tests/compiler/ref/override-add-byref-return.phpt

@@ -0,0 +1,71 @@
+--TEST--
+An override may add a by-reference return and preserve alias semantics
+--FILE--
+<?php
+
+class ByRefReturnParent
+{
+    public function value(): int
+    {
+        return -1;
+    }
+}
+
+final class ByRefReturnChild extends ByRefReturnParent
+{
+    private int $stored = 10;
+
+    public function &value(): int
+    {
+        return $this->stored;
+    }
+}
+
+class StaticByRefReturnParent
+{
+    public static function value(): int
+    {
+        return -1;
+    }
+}
+
+final class StaticByRefReturnChild extends StaticByRefReturnParent
+{
+    private static int $stored = 20;
+
+    public static function &value(): int
+    {
+        return self::$stored;
+    }
+}
+
+function readByRefReturnParent(ByRefReturnParent $value): int
+{
+    return $value->value();
+}
+
+function main(): void
+{
+    $child = new ByRefReturnChild();
+    var_dump(readByRefReturnParent($child));
+
+    $instanceAlias =& $child->value();
+    $instanceAlias = 42;
+    var_dump($child->value());
+    var_dump(readByRefReturnParent($child));
+
+    $instanceCopy = $child->value();
+    $instanceCopy = 99;
+    var_dump($child->value());
+
+    $staticAlias =& StaticByRefReturnChild::value();
+    $staticAlias = 84;
+    var_dump(StaticByRefReturnChild::value());
+}
+?>
+--EXPECT--
+int(10)
+int(42)
+int(42)
+int(42)
+int(84)