[RFC] Allow Readonly Property Defaults

NEWS

@@ -7,6 +7,7 @@ PHP                                                                        NEWS
   . Changed run-tests.php to run in parallel by default, using up to 10
     automatically detected workers. Pass -j1 for sequential execution.
     (NickSdot)
+  . Allowed readonly properties to declare default values. (NickSdot)
   . Changed run-tests.php to run test subprocesses without a shell where
     possible. (NickSdot)
   . Fixed GH-23083 (SEGV build_trace_args in zend_exceptions.c with

UPGRADING

@@ -299,6 +299,8 @@ PHP 8.6 UPGRADE NOTES
 ========================================
 
 - Core:
+  . Readonly properties may now declare default values.
+    RFC: https://wiki.php.net/rfc/readonly_property_defaults
   . It is now possible to use reference assign on WeakMap without the key
     needing to be present beforehand.
   . It is now possible to define the __debugInfo() magic method on enums.

Zend/tests/readonly_classes/readonly_with_property_default.phpt

@@ -0,0 +1,36 @@
+--TEST--
+Properties of a readonly class may have default values
+--FILE--
+<?php
+
+readonly class Foo
+{
+    public int $bar = 1;
+    public ?string $nullable = null;
+
+    public function __construct()
+    {
+        try {
+            $this->bar = 2;
+        } catch (Error $e) {
+            echo $e::class, ': ', $e->getMessage(), PHP_EOL;
+        }
+    }
+}
+
+$foo = new Foo();
+var_dump($foo->bar);
+var_dump($foo->nullable);
+
+try {
+    $foo->bar = 3;
+} catch (Error $e) {
+    echo $e::class, ': ', $e->getMessage(), PHP_EOL;
+}
+
+?>
+--EXPECT--
+Error: Cannot modify readonly property Foo::$bar
+int(1)
+NULL
+Error: Cannot modify readonly property Foo::$bar

Zend/tests/readonly_classes/readonly_with_property_default_trait.phpt

@@ -0,0 +1,25 @@
+--TEST--
+Readonly class may use readonly trait property with default value
+--FILE--
+<?php
+
+trait TDefault {
+    public readonly int $prop = 2;
+}
+
+readonly class A {
+    use TDefault;
+}
+
+var_dump(new A()->prop);
+
+class B {
+    use TDefault;
+}
+
+var_dump(new B()->prop);
+
+?>
+--EXPECT--
+int(2)
+int(2)

Zend/tests/readonly_props/readonly_clone_success1.phpt

@@ -23,6 +23,41 @@ var_dump($foo2);
 
 var_dump(clone $foo2);
 
+class FooWithDefault {
+    public readonly int $bar = 1;
+
+    public function __clone()
+    {
+        $this->bar++;
+    }
+}
+
+$fooWithDefault = new FooWithDefault();
+
+var_dump(clone $fooWithDefault);
+
+$fooWithDefault2 = clone $fooWithDefault;
+var_dump($fooWithDefault2);
+
+var_dump(clone $fooWithDefault2);
+
+class FooWithDefaultCloneWith {
+    public readonly int $bar = 1;
+
+    public function withBar(int $bar)
+    {
+        return clone($this, ['bar' => $bar]);
+    }
+}
+
+$clone = new FooWithDefaultCloneWith();
+var_dump($clone);
+
+$clone2 = $clone->withBar(2);
+var_dump($clone2);
+
+var_dump($clone2->withBar(0));
+
 ?>
 --EXPECTF--
 object(Foo)#%d (%d) {
@@ -37,3 +72,27 @@ object(Foo)#%d (%d) {
   ["bar"]=>
   int(3)
 }
+object(FooWithDefault)#%d (%d) {
+  ["bar"]=>
+  int(2)
+}
+object(FooWithDefault)#%d (%d) {
+  ["bar"]=>
+  int(2)
+}
+object(FooWithDefault)#%d (%d) {
+  ["bar"]=>
+  int(3)
+}
+object(FooWithDefaultCloneWith)#%d (%d) {
+  ["bar"]=>
+  int(1)
+}
+object(FooWithDefaultCloneWith)#%d (%d) {
+  ["bar"]=>
+  int(2)
+}
+object(FooWithDefaultCloneWith)#%d (%d) {
+  ["bar"]=>
+  int(0)
+}

Zend/tests/readonly_props/readonly_trait_match.phpt

@@ -13,7 +13,20 @@ class C {
     use T1, T2;
 }
 
+trait TDefault1 {
+    public readonly int $prop = 1;
+}
+trait TDefault2 {
+    public readonly int $prop = 1;
+}
+class CDefault {
+    use TDefault1, TDefault2;
+}
+
+var_dump(new CDefault()->prop);
+
 ?>
 ===DONE===
 --EXPECT--
+int(1)
 ===DONE===

Zend/tests/readonly_props/readonly_with_default.phpt

@@ -3,17 +3,43 @@ Readonly property with default value
 --FILE--
 <?php
 
+enum E {
+    case Case;
+}
+
 class Test {
     public readonly int $prop = 1;
+    public readonly string $className = self::class;
+    public readonly ?string $nullable = null;
+    public readonly array $array = [1, "two" => 2];
+    public readonly E $enum = E::Case;
+    public readonly string $enumString = E::Case->name;
 }
 
 $test = new Test;
+var_dump($test->prop);
+var_dump($test->className);
+var_dump($test->nullable);
+var_dump($test->array);
+var_dump($test->enum);
+var_dump($test->enumString);
 try {
     $test->prop = 2;
 } catch (Error $e) {
-    echo $e->getMessage(), "\n";
+    echo $e::class, ': ', $e->getMessage(), PHP_EOL;
 }
 
 ?>
---EXPECTF--
-Fatal error: Readonly property Test::$prop cannot have default value in %s on line %d
+--EXPECT--
+int(1)
+string(4) "Test"
+NULL
+array(2) {
+  [0]=>
+  int(1)
+  ["two"]=>
+  int(2)
+}
+enum(E::Case)
+string(4) "Case"
+Error: Cannot modify readonly property Test::$prop

Zend/tests/readonly_props/readonly_with_default_abstract_get_set_implicit_set.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Readonly property with default value has restricted set visibility for get/set abstract property
+--DESCRIPTION--
+The error message should be improved, the set access level comes from readonly.
+--FILE--
+<?php
+
+abstract class P {
+    public abstract int $prop { get; set; }
+}
+
+class C extends P {
+    public readonly int $prop = 42;
+}
+
+?>
+--EXPECTF--
+Fatal error: Set access level of C::$prop must be omitted (as in class P) in %s on line %d

Zend/tests/readonly_props/readonly_with_default_asymmetric_visibility.phpt

@@ -0,0 +1,34 @@
+--TEST--
+Readonly property with default value and asymmetric visibility
+--FILE--
+<?php
+
+class Test {
+    public readonly int $default = 1;
+    public private(set) readonly int $private = 2;
+    public protected(set) readonly int $protected = 3;
+    public public(set) readonly int $public = 4;
+}
+
+$test = new Test();
+
+foreach (['default', 'private', 'protected', 'public'] as $prop) {
+    $before = $test->$prop;
+    try {
+        $test->$prop = 42;
+    } catch (Error $e) {
+        echo $e::class, ': ', $e->getMessage(), PHP_EOL;
+    }
+    echo "$$prop before $before, after {$test->$prop}", PHP_EOL;
+}
+
+?>
+--EXPECT--
+Error: Cannot modify readonly property Test::$default
+$default before 1, after 1
+Error: Cannot modify readonly property Test::$private
+$private before 2, after 2
+Error: Cannot modify readonly property Test::$protected
+$protected before 3, after 3
+Error: Cannot modify readonly property Test::$public
+$public before 4, after 4

Zend/tests/readonly_props/readonly_with_default_inheritance.phpt

@@ -0,0 +1,40 @@
+--TEST--
+Readonly property with default value and inheritance
+--FILE--
+<?php
+
+class ParentDefault {
+    public readonly int $prop = 1;
+}
+
+class ChildInherits extends ParentDefault {}
+
+class ChildOverrides extends ParentDefault {
+    public readonly int $prop = 2;
+}
+
+class PrivateParent {
+    private readonly int $prop = 3;
+
+    public function getParentProp(): int {
+        return $this->prop;
+    }
+}
+
+class PrivateChild extends PrivateParent {
+    public readonly int $prop = 4;
+}
+
+var_dump(new ChildInherits()->prop);
+var_dump(new ChildOverrides()->prop);
+
+$privateChild = new PrivateChild();
+var_dump($privateChild->getParentProp());
+var_dump($privateChild->prop);
+
+?>
+--EXPECT--
+int(1)
+int(2)
+int(3)
+int(4)

Zend/tests/readonly_props/readonly_with_default_interface_get_only.phpt

@@ -0,0 +1,17 @@
+--TEST--
+Readonly property with default value satisfies get-only interface property
+--FILE--
+<?php
+
+interface I {
+    public int $prop { get; }
+}
+
+class C implements I {
+    public readonly int $prop = 42;
+}
+
+var_dump(new C()->prop);
+?>
+--EXPECT--
+int(42)

Zend/tests/readonly_props/readonly_with_default_interface_get_set.phpt

@@ -0,0 +1,16 @@
+--TEST--
+Readonly public(set) property with default value does not satisfy get/set interface property
+--FILE--
+<?php
+
+interface I {
+    public int $prop { get; set; }
+}
+
+// does not satisfy set
+class C implements I {
+    public public(set) readonly int $prop = 42;
+}
+?>
+--EXPECTF--
+Fatal error: Class C contains 1 abstract method and must therefore be declared abstract or implement the remaining method (I::$prop::set) in %s on line %d

Zend/tests/readonly_props/readonly_with_default_interface_get_set_implicit_set.phpt

@@ -0,0 +1,17 @@
+--TEST--
+Readonly property with default value has restricted set visibility for get/set interface property
+--DESCRIPTION--
+The error message should be improved, the set access level comes from readonly. Ref: Zend/tests/property_hooks/interface_get_set_readonly.phpt
+--FILE--
+<?php
+
+interface I {
+    public int $prop { get; set; }
+}
+
+class C implements I {
+    public readonly int $prop = 42;
+}
+?>
+--EXPECTF--
+Fatal error: Set access level of C::$prop must be omitted (as in class I) in %s on line %d

Zend/tests/readonly_props/readonly_with_default_trait_mismatch.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Readonly trait property default value mismatch
+--FILE--
+<?php
+
+trait T1 {
+    public readonly int $prop = 1;
+}
+
+trait T2 {
+    public readonly int $prop = 2;
+}
+
+class C {
+    use T1, T2;
+}
+
+?>
+--EXPECTF--
+Fatal error: T1 and T2 define the same property ($prop) in the composition of C. However, the definition differs and is considered incompatible. Class was composed in %s on line %d