Allow promoted readonly properties to be reassigned once in constructor

Zend/tests/readonly_props/cpp_reassign_basic.phpt

@@ -0,0 +1,28 @@
+--TEST--
+Promoted readonly property reassignment in constructor - basic
+--FILE--
+<?php
+
+class Point {
+    public function __construct(
+        public readonly int $x = 0,
+        public readonly int $y = 0,
+    ) {
+        // Reassign promoted readonly properties - allowed once
+        $this->x = abs($x);
+        $this->y = abs($y);
+    }
+}
+
+$point = new Point();
+var_dump($point->x, $point->y);
+
+$point2 = new Point(-5, -3);
+var_dump($point2->x, $point2->y);
+
+?>
+--EXPECT--
+int(0)
+int(0)
+int(5)
+int(3)

Zend/tests/readonly_props/cpp_reassign_child_class.phpt

@@ -0,0 +1,89 @@
+--TEST--
+Promoted readonly property reassignment in constructor - child cannot reassign parent's property
+--FILE--
+<?php
+
+// Case 1: Parent does NOT use reassignment, child still cannot reassign
+class Parent1 {
+    public function __construct(
+        public readonly string $prop = 'parent default',
+    ) {
+        // Parent does NOT reassign here
+    }
+}
+
+class Child1 extends Parent1 {
+    public function __construct() {
+        parent::__construct();
+        // Child cannot reassign parent-owned promoted property
+        try {
+            $this->prop = 'child override';
+        } catch (Throwable $e) {
+            echo get_class($e), ": ", $e->getMessage(), "\n";
+        }
+    }
+}
+
+$child = new Child1();
+var_dump($child->prop);
+
+// Case 2: Parent USES reassignment, child cannot
+class Parent2 {
+    public function __construct(
+        public readonly string $prop = 'parent default',
+    ) {
+        $this->prop = 'parent set';  // Uses the one reassignment
+    }
+}
+
+class Child2 extends Parent2 {
+    public function __construct() {
+        parent::__construct();
+        // Child cannot reassign parent-owned promoted property
+        try {
+            $this->prop = 'child override';
+        } catch (Throwable $e) {
+            echo get_class($e), ": ", $e->getMessage(), "\n";
+        }
+    }
+}
+
+$child2 = new Child2();
+var_dump($child2->prop);
+
+// Case 3: Child with its own promoted property
+class Parent3 {
+    public function __construct(
+        public readonly string $parentProp = 'parent default',
+    ) {
+        // Parent does NOT reassign here
+    }
+}
+
+class Child3 extends Parent3 {
+    public function __construct(
+        public readonly string $childProp = 'child default',
+    ) {
+        parent::__construct();
+        // Child cannot reassign parent's property, but can reassign its own
+        try {
+            $this->parentProp = 'child set parent';
+        } catch (Throwable $e) {
+            echo get_class($e), ": ", $e->getMessage(), "\n";
+        }
+        $this->childProp = 'child set own';
+    }
+}
+
+$child3 = new Child3();
+var_dump($child3->parentProp, $child3->childProp);
+
+?>
+--EXPECT--
+Error: Cannot modify readonly property Parent1::$prop
+string(14) "parent default"
+Error: Cannot modify readonly property Parent2::$prop
+string(10) "parent set"
+Error: Cannot modify readonly property Parent3::$parentProp
+string(14) "parent default"
+string(13) "child set own"

Zend/tests/readonly_props/cpp_reassign_child_preempt_parent.phpt

@@ -0,0 +1,31 @@
+--TEST--
+Promoted readonly property reassignment in constructor - child preempt then parent ctor throws
+--FILE--
+<?php
+
+class ParentCPP {
+    public function __construct(
+        public readonly string $prop = 'parent default',
+    ) {
+        $this->prop = 'parent set';
+    }
+}
+
+class ChildCPP extends ParentCPP {
+    public function __construct() {
+        $this->prop = 'child set';
+        try {
+            parent::__construct();
+        } catch (Throwable $e) {
+            echo get_class($e), ": ", $e->getMessage(), "\n";
+        }
+    }
+}
+
+$c = new ChildCPP();
+var_dump($c->prop);
+
+?>
+--EXPECT--
+Error: Cannot modify readonly property ParentCPP::$prop
+string(9) "child set"

Zend/tests/readonly_props/cpp_reassign_child_redefine.phpt

@@ -0,0 +1,84 @@
+--TEST--
+Promoted readonly property reassignment in constructor - child redefines parent property
+--FILE--
+<?php
+
+// Case 1: Parent uses CPP, child redefines as non-promoted, child tries to reassign.
+// P1 owns the CPP reassignment window; it is cleared when P1's constructor exits,
+// before C1's body runs. So C1's write attempt fails.
+class P1 {
+    public function __construct(
+        public readonly string $x = 'P',
+    ) {}
+}
+
+class C1 extends P1 {
+    public readonly string $x;
+
+    public function __construct() {
+        parent::__construct();
+        try {
+            $this->x = 'C';
+        } catch (Throwable $e) {
+            echo get_class($e), ": ", $e->getMessage(), "\n";
+        }
+    }
+}
+
+$c1 = new C1();
+var_dump($c1->x);
+
+// Case 2: Parent uses CPP and reassigns; child redefines as non-promoted.
+// The child does not use CPP, so it does not claim CPP ownership of the property.
+// P2's CPP "owns" the reassignment window: P2's body write succeeds.
+class P2 {
+    public function __construct(
+        public readonly string $x = 'P1',
+    ) {
+        $this->x = 'P2';
+    }
+}
+
+class C2 extends P2 {
+    public readonly string $x;
+
+    public function __construct() {
+        parent::__construct();
+    }
+}
+
+$c2 = new C2();
+var_dump($c2->x);
+
+// Case 3: Parent uses CPP, child uses CPP redefinition.
+// Child's CPP opens the reassignment window for C3::$x. When parent::__construct()
+// runs, P3's CPP tries to initialize C3::$x again, which must fail since C3
+// owns the property and has already initialized it.
+class P3 {
+    public function __construct(
+        public readonly string $x = 'P',
+    ) {}
+}
+
+class C3 extends P3 {
+    public function __construct(
+        public readonly string $x = 'C1',
+    ) {
+        try {
+            parent::__construct();
+        } catch (Throwable $e) {
+            echo get_class($e), ": ", $e->getMessage(), "\n";
+        }
+    }
+}
+
+$c3 = new C3();
+var_dump($c3->x);
+
+?>
+--EXPECT--
+Error: Cannot modify readonly property C1::$x
+string(1) "P"
+string(2) "P2"
+Error: Cannot modify readonly property C3::$x
+string(2) "C1"

Zend/tests/readonly_props/cpp_reassign_conditional.phpt

@@ -0,0 +1,23 @@
+--TEST--
+Promoted readonly property reassignment in constructor - conditional initialization
+--FILE--
+<?php
+
+class Config {
+    public function __construct(
+        public readonly ?string $cacheDir = null,
+    ) {
+        $this->cacheDir ??= '/tmp/app_cache';
+    }
+}
+
+$config1 = new Config();
+var_dump($config1->cacheDir);
+
+$config2 = new Config('/custom/cache');
+var_dump($config2->cacheDir);
+
+?>
+--EXPECT--
+string(14) "/tmp/app_cache"
+string(13) "/custom/cache"

Zend/tests/readonly_props/cpp_reassign_different_object.phpt

@@ -0,0 +1,34 @@
+--TEST--
+Promoted readonly property reassignment in constructor - different object fails
+--FILE--
+<?php
+
+// Constructor can modify its own promoted property, but not another object's
+class Foo {
+    public function __construct(
+        public readonly int $x = 0,
+        ?Foo $other = null,
+    ) {
+        $this->x = $x * 2;
+        if ($other !== null) {
+            try {
+                $other->x = 999;
+            } catch (Throwable $e) {
+                echo get_class($e), ": ", $e->getMessage(), "\n";
+            }
+        }
+    }
+}
+
+$a = new Foo(5);
+var_dump($a->x);
+
+$b = new Foo(3, $a);
+var_dump($a->x, $b->x);  // $a unchanged
+
+?>
+--EXPECT--
+int(10)
+Error: Cannot modify readonly property Foo::$x
+int(10)
+int(6)

Zend/tests/readonly_props/cpp_reassign_direct_ctor_call.phpt

@@ -0,0 +1,29 @@
+--TEST--
+Promoted readonly properties cannot be reassigned when __construct() is called directly
+--FILE--
+<?php
+
+class Foo {
+    public function __construct(
+        public readonly string $value = 'default',
+    ) {
+        $this->value = strtoupper($this->value);
+    }
+}
+
+$obj = new Foo('hello');
+var_dump($obj->value);
+
+// Direct call fails: CPP assignment cannot reinitialize an already-set property
+try {
+    $obj->__construct('world');
+} catch (Throwable $e) {
+    echo get_class($e), ": ", $e->getMessage(), "\n";
+}
+var_dump($obj->value);
+
+?>
+--EXPECT--
+string(5) "HELLO"
+Error: Cannot modify readonly property Foo::$value
+string(5) "HELLO"

Zend/tests/readonly_props/cpp_reassign_indirect_allowed.phpt

@@ -0,0 +1,47 @@
+--TEST--
+Promoted readonly property reassignment in constructor - indirect reassignment allowed
+--FILE--
+<?php
+
+// Reassignment IS allowed in methods called by the constructor
+class CalledMethod {
+    public function __construct(
+        public readonly string $prop = 'default',
+    ) {
+        $this->initProp();
+    }
+
+    private function initProp(): void {
+        $this->prop = 'from method';
+    }
+}
+
+$cm = new CalledMethod();
+var_dump($cm->prop);
+
+// But second reassignment still fails
+class MultipleReassign {
+    public function __construct(
+        public readonly string $prop = 'default',
+    ) {
+        $this->initProp("first from method");
+        try {
+            $this->initProp("second from method");  // Second call - should fail
+        } catch (Throwable $e) {
+            echo get_class($e), ": ", $e->getMessage(), "\n";
+        }
+    }
+
+    private function initProp(string $v): void {
+        $this->prop = $v;
+    }
+}
+
+$mr = new MultipleReassign();
+var_dump($mr->prop);
+
+?>
+--EXPECT--
+string(11) "from method"
+Error: Cannot modify readonly property MultipleReassign::$prop
+string(17) "first from method"