Allow ZEND_ACC_VIRTUAL to be used to not have property backing storage without resorting to hooks

This is useful to reduce the memory usage of objects that don't actually
use the backing storage. Examples are XMLReader and DOM. When the
properties were added to the stubs, these objects became much much
bigger, which is a waste of memory.

Closes GH-11644.

Work towards GH-13988.

Author: nielsdos

build/gen_stub.php

@@ -2907,6 +2907,7 @@ class PropertyInfo extends VariableLike
     public ?Expr $defaultValue;
     public ?string $defaultValueString;
     public bool $isDocReadonly;
+    public bool $isVirtual;
 
     /**
      * @var AttributeInfo[] $attributes
@@ -2920,6 +2921,7 @@ public function __construct(
         ?Expr $defaultValue,
         ?string $defaultValueString,
         bool $isDocReadonly,
+        bool $isVirtual,
         ?string $link,
         ?int $phpVersionIdMinimumCompatibility,
         array $attributes,
@@ -2930,6 +2932,7 @@ public function __construct(
         $this->defaultValue = $defaultValue;
         $this->defaultValueString = $defaultValueString;
         $this->isDocReadonly = $isDocReadonly;
+        $this->isVirtual = $isVirtual;
         parent::__construct($flags, $type, $phpDocType, $link, $phpVersionIdMinimumCompatibility, $attributes, $exposedDocComment);
     }
 
@@ -3045,6 +3048,10 @@ protected function getFlagsByPhpVersion(): array
             $flags = $this->addFlagForVersionsAbove($flags, "ZEND_ACC_READONLY", PHP_82_VERSION_ID);
         }
 
+        if ($this->isVirtual) {
+            $flags = $this->addFlagForVersionsAbove($flags, "ZEND_ACC_VIRTUAL", PHP_84_VERSION_ID);
+        }
+
         return $flags;
     }
 
@@ -4424,6 +4431,7 @@ function parseProperty(
 ): PropertyInfo {
     $phpDocType = null;
     $isDocReadonly = false;
+    $isVirtual = false;
     $link = null;
 
     if ($comments) {
@@ -4435,6 +4443,8 @@ function parseProperty(
                 $isDocReadonly = true;
             } elseif ($tag->name === 'link') {
                 $link = $tag->value;
+            } elseif ($tag->name === 'virtual') {
+                $isVirtual = true;
             }
         }
     }
@@ -4463,6 +4473,7 @@ function parseProperty(
         $property->default,
         $property->default ? $prettyPrinter->prettyPrintExpr($property->default) : null,
         $isDocReadonly,
+        $isVirtual,
         $link,
         $phpVersionIdMinimumCompatibility,
         $attributes,

ext/reflection/php_reflection.c

@@ -6041,7 +6041,7 @@ ZEND_METHOD(ReflectionProperty, getSettableType)
 	}
 
 	/* Get-only virtual property can never be written to. */
-	if ((prop->flags & ZEND_ACC_VIRTUAL) && !prop->hooks[ZEND_PROPERTY_HOOK_SET]) {
+	if (prop->hooks && (prop->flags & ZEND_ACC_VIRTUAL) && !prop->hooks[ZEND_PROPERTY_HOOK_SET]) {
 		zend_type never_type = ZEND_TYPE_INIT_CODE(IS_NEVER, 0, 0);
 		reflection_type_factory(never_type, return_value, 0);
 		return;