[RFC] Add #[\DelayedTargetValidation] attribute

UPGRADING

@@ -53,6 +53,8 @@ PHP 8.5 UPGRADE NOTES
   . Applying #[\Attribute] to an abstract class, enum, interface, or trait triggers
     an error during compilation. Previously, the attribute could be added, but when
     ReflectionAttribute::newInstance() was called an error would be thrown.
+    The error can be delayed from compilation to runtime using the new
+    #[\DelayedTargetValidation] attribute.
 
 - DOM:
   . Cloning a DOMNamedNodeMap, DOMNodeList, Dom\NamedNodeMap, Dom\NodeList,
@@ -180,6 +182,11 @@ PHP 8.5 UPGRADE NOTES
     RFC: https://wiki.php.net/rfc/final_promotion
   . #[\Override] can now be applied to properties.
     RFC: https://wiki.php.net/rfc/override_properties
+  . The #[\DelayedTargetValidation] attribute can be used to suppress
+    compile-time errors from core (or extension) attributes that are used on
+    invalid targets. These errors are instead reported at runtime if and when
+    ReflectionAttribute::newInstance() is called.
+    RFC: https://wiki.php.net/rfc/delayedtargetvalidation_attribute
 
 - Curl:
   . Added support for share handles that are persisted across multiple PHP
@@ -506,6 +513,11 @@ PHP 8.5 UPGRADE NOTES
     hooks are final, and whether the property is virtual. This also affects
     the output of ReflectionClass::__toString() when a class contains hooked
     properties.
+  . ReflectionAttribute::newInstance() can now throw errors for internal
+    attributes if the attribute was applied on an invalid target and the
+    error was delayed from compile-time to runtime via the
+    #[\DelayedTargetValidation] attribute.
+    RFC: https://wiki.php.net/rfc/delayedtargetvalidation_attribute
 
 - Session:
   . session_start is stricter in regard to the option argument.
@@ -623,6 +635,12 @@ PHP 8.5 UPGRADE NOTES
 7. New Classes and Interfaces
 ========================================
 
+- Core:
+  . DelayedTargetValidation is an attribute that, when added, delays any errors
+    from *other* internal attributes about being applied to invalid targets from
+    compile-time to runtime.
+    RFC: https://wiki.php.net/rfc/delayedtargetvalidation_attribute
+
 - Curl:
   . CurlSharePersistentHandle representing a share handle that is persisted
     across multiple PHP requests.

UPGRADING.INTERNALS

@@ -28,6 +28,18 @@ PHP 8.5 INTERNALS UPGRADE NOTES
     extra layer of indirection can be removed. In other cases a zval can
     be heap-allocated and stored in the pointer as a minimal change to keep
     compatibility.
+  . The `target` parameter for validator callbacks for internal attributes
+    can now include in the bitmask the new flags
+    ZEND_ATTRIBUTE_NO_TARGET_VALIDATION and
+    ZEND_ATTRIBUTE_DELAYED_TARGET_VALIDATION. The first indicates that, if the
+    attribute is being applied to an invalid target, no error should be thrown
+    at compile time. The second indicates that validation is being performed
+    at runtime and that if an attribute is being applied to an invalid target,
+    a catchable error should be thrown. Target validation is different from
+    the actual functionality of the attribute; e.g. the #[\Override] attribute
+    will trigger an error if the function does not override a method from the
+    parent class or from an interface; that error does not get delayed.
+    RFC: https://wiki.php.net/rfc/delayedtargetvalidation_attribute
 
 - Hash
   . Hash functions now use proper hash_spec_result enum for return values

Zend/tests/attributes/delayed_target_validation/has_runtime_errors.phpt

@@ -0,0 +1,282 @@
+--TEST--
+#[\DelayedTargetValidation] has errors at runtime
+--FILE--
+<?php
+
+#[DelayedTargetValidation]
+#[NoDiscard]
+class Demo {
+
+	#[DelayedTargetValidation]
+	#[Attribute]
+	public const FOO = 'BAR';
+
+	#[DelayedTargetValidation]
+	#[Attribute]
+	public string $v1;
+
+	public string $v2 {
+		#[DelayedTargetValidation]
+		#[Attribute]
+		get => $this->v2;
+		#[DelayedTargetValidation]
+		#[Attribute]
+		set => $value;
+	}
+
+	#[DelayedTargetValidation]
+	#[Attribute]
+	public function __construct(
+		#[DelayedTargetValidation]
+		#[Attribute]
+		public string $v3
+	) {
+		$this->v1 = $v3;
+		echo __METHOD__ . "\n";
+	}
+}
+
+#[DelayedTargetValidation]
+#[Attribute]
+function demoFn() {
+	echo __FUNCTION__ . "\n";
+}
+
+#[DelayedTargetValidation]
+#[Attribute]
+const EXAMPLE = true;
+
+$cases = [
+	new ReflectionClass('Demo'),
+	new ReflectionClassConstant('Demo', 'FOO'),
+	new ReflectionProperty('Demo', 'v1'),
+	new ReflectionProperty('Demo', 'v2')->getHook(PropertyHookType::Get),
+	new ReflectionProperty('Demo', 'v2')->getHook(PropertyHookType::Set),
+	new ReflectionMethod('Demo', '__construct'),
+	new ReflectionParameter([ 'Demo', '__construct' ], 'v3'),
+	new ReflectionProperty('Demo', 'v3'),
+	new ReflectionFunction('demoFn'),
+	new ReflectionConstant('EXAMPLE'),
+];
+foreach ($cases as $r) {
+	echo str_repeat("*", 20) . "\n";
+	echo $r . "\n";
+	$attributes = $r->getAttributes();
+	var_dump($attributes);
+	try {
+		$attributes[1]->newInstance();
+	} catch (Error $e) {
+		echo get_class($e) . ": " . $e->getMessage() . "\n";
+	}
+}
+
+?>
+--EXPECTF--
+********************
+Class [ <user> <iterateable> class Demo ] {
+  @@ %s %d-%d
+
+  - Constants [1] {
+    Constant [ public string FOO ] { BAR }
+  }
+
+  - Static properties [0] {
+  }
+
+  - Static methods [0] {
+  }
+
+  - Properties [3] {
+    Property [ public string $v1 ]
+    Property [ public string $v2 { get; set; } ]
+    Property [ public string $v3 ]
+  }
+
+  - Methods [1] {
+    Method [ <user, ctor> public method __construct ] {
+      @@ %s %d - %d
+
+      - Parameters [1] {
+        Parameter #0 [ <required> string $v3 ]
+      }
+    }
+  }
+}
+
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "NoDiscard"
+  }
+}
+Error: Attribute "NoDiscard" cannot target class (allowed targets: function, method)
+********************
+Constant [ public string FOO ] { BAR }
+
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "Attribute"
+  }
+}
+Error: Attribute "Attribute" cannot target class constant (allowed targets: class)
+********************
+Property [ public string $v1 ]
+
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "Attribute"
+  }
+}
+Error: Attribute "Attribute" cannot target property (allowed targets: class)
+********************
+Method [ <user> public method $v2::get ] {
+  @@ %s %d - %d
+
+  - Parameters [0] {
+  }
+  - Return [ string ]
+}
+
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "Attribute"
+  }
+}
+Error: Attribute "Attribute" cannot target method (allowed targets: class)
+********************
+Method [ <user> public method $v2::set ] {
+  @@ %s %d - %d
+
+  - Parameters [1] {
+    Parameter #0 [ <required> string $value ]
+  }
+  - Return [ void ]
+}
+
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "Attribute"
+  }
+}
+Error: Attribute "Attribute" cannot target method (allowed targets: class)
+********************
+Method [ <user, ctor> public method __construct ] {
+  @@ %s %d - %d
+
+  - Parameters [1] {
+    Parameter #0 [ <required> string $v3 ]
+  }
+}
+
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "Attribute"
+  }
+}
+Error: Attribute "Attribute" cannot target method (allowed targets: class)
+********************
+Parameter #0 [ <required> string $v3 ]
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "Attribute"
+  }
+}
+Error: Attribute "Attribute" cannot target parameter (allowed targets: class)
+********************
+Property [ public string $v3 ]
+
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "Attribute"
+  }
+}
+Error: Attribute "Attribute" cannot target property (allowed targets: class)
+********************
+Function [ <user> function demoFn ] {
+  @@ %s %d - %d
+}
+
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "Attribute"
+  }
+}
+Error: Attribute "Attribute" cannot target function (allowed targets: class)
+********************
+Constant [ bool EXAMPLE ] { 1 }
+
+array(2) {
+  [0]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(23) "DelayedTargetValidation"
+  }
+  [1]=>
+  object(ReflectionAttribute)#%d (1) {
+    ["name"]=>
+    string(9) "Attribute"
+  }
+}
+Error: Attribute "Attribute" cannot target constant (allowed targets: class)