Support Closures in constant expressions (php#16458)

RFC: https://wiki.php.net/rfc/closures_in_const_expr

Co-authored-by: Volker Dusch <volker@tideways-gmbh.com>
Co-authored-by: Ilija Tovilo <ilija.tovilo@me.com>
Co-authored-by: Arthur Kurbidaev <artkurbidaev@gmail.com>

NEWS

@@ -10,6 +10,8 @@ PHP                                                                        NEWS
   . Fixed bug GH-16665 (\array and \callable should not be usable in
     class_alias). (nielsdos)
   . Added PHP_BUILD_DATE constant. (cmb)
+  . Added support for Closures in constant expressions. (timwolla,
+    Volker Dusch)
 
 - Curl:
   . Added curl_multi_get_handles(). (timwolla)

UPGRADING

@@ -44,6 +44,10 @@ PHP 8.5 UPGRADE NOTES
 2. New Features
 ========================================
 
+- Core:
+  . Added support for Closures in constant expressions.
+    RFC: https://wiki.php.net/rfc/closures_in_const_expr
+
 - DOM:
   . Added Dom\Element::$outerHTML.
 

Zend/tests/closure_const_expr/attributes.phpt

@@ -0,0 +1,57 @@
+--TEST--
+Allow defining closures in attributes
+--EXTENSIONS--
+reflection
+--FILE--
+<?php
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+class Attr {
+    public function __construct(public Closure $value) {
+      $value('foo');
+    }
+}
+
+#[Attr(static function () { })]
+#[Attr(static function (...$args) {
+  var_dump($args);
+})]
+class C {}
+
+foreach ((new ReflectionClass(C::class))->getAttributes() as $reflectionAttribute) {
+    var_dump($reflectionAttribute->newInstance());
+}
+
+?>
+--EXPECTF--
+object(Attr)#%d (1) {
+  ["value"]=>
+  object(Closure)#%d (3) {
+    ["name"]=>
+    string(%d) "{closure:%s:%d}"
+    ["file"]=>
+    string(%d) "%s"
+    ["line"]=>
+    int(%d)
+  }
+}
+array(1) {
+  [0]=>
+  string(3) "foo"
+}
+object(Attr)#%d (1) {
+  ["value"]=>
+  object(Closure)#%d (4) {
+    ["name"]=>
+    string(%d) "{closure:%s:%d}"
+    ["file"]=>
+    string(%d) "%s"
+    ["line"]=>
+    int(%d)
+    ["parameter"]=>
+    array(1) {
+      ["$args"]=>
+      string(10) "<optional>"
+    }
+  }
+}

Zend/tests/closure_const_expr/attributes_ast_printing.phpt

@@ -0,0 +1,41 @@
+--TEST--
+AST printing for closures in attributes
+--FILE--
+<?php
+
+// Do not use `false &&` to fully evaluate the function / class definition.
+
+try {
+    \assert(
+        !
+        #[Attr(static function ($foo) {
+            echo $foo;
+        })]
+        function () { }
+    );
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+try {
+    \assert(
+        !
+        new #[Attr(static function ($foo) {
+            echo $foo;
+        })]
+        class {}
+    );
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+assert(!#[Attr(static function ($foo) {
+    echo $foo;
+})] function () {
+})
+assert(!new #[Attr(static function ($foo) {
+    echo $foo;
+})] class {
+})

Zend/tests/closure_const_expr/attributes_scope_001.phpt

@@ -0,0 +1,28 @@
+--TEST--
+Closure in attribute may access private variables
+--EXTENSIONS--
+reflection
+--FILE--
+<?php
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+class Attr {
+    public function __construct(public Closure $value) {}
+}
+
+#[Attr(static function (C $c) {
+    echo $c->secret, PHP_EOL;
+})]
+class C {
+    public function __construct(
+        private string $secret,
+    ) {}
+}
+
+foreach ((new ReflectionClass(C::class))->getAttributes() as $reflectionAttribute) {
+    ($reflectionAttribute->newInstance()->value)(new C('secret'));
+}
+
+?>
+--EXPECT--
+secret

Zend/tests/closure_const_expr/attributes_scope_002.phpt

@@ -0,0 +1,35 @@
+--TEST--
+Closure in attribute may not access unrelated private variables
+--EXTENSIONS--
+reflection
+--FILE--
+<?php
+
+#[Attribute(Attribute::TARGET_CLASS | Attribute::IS_REPEATABLE)]
+class Attr {
+    public function __construct(public Closure $value) {}
+}
+
+#[Attr(static function (E $e) {
+    echo $e->secret, PHP_EOL;
+})]
+class C {
+}
+
+class E {
+    public function __construct(
+        private string $secret,
+    ) {}
+}
+
+foreach ((new ReflectionClass(C::class))->getAttributes() as $reflectionAttribute) {
+    ($reflectionAttribute->newInstance()->value)(new E('secret'));
+}
+
+?>
+--EXPECTF--
+Fatal error: Uncaught Error: Cannot access private property E::$secret in %s:%d
+Stack trace:
+#0 %s(%d): C::{closure:%s:%d}(Object(E))
+#1 {main}
+  thrown in %s on line %d

Zend/tests/closure_const_expr/basic.phpt

@@ -0,0 +1,23 @@
+--TEST--
+Allow defining Closures in const expressions.
+--FILE--
+<?php
+
+const Closure = static function () {
+    echo "called", PHP_EOL;
+};
+
+var_dump(Closure);
+(Closure)();
+
+?>
+--EXPECTF--
+object(Closure)#%d (3) {
+  ["name"]=>
+  string(%d) "{closure:%s:%d}"
+  ["file"]=>
+  string(%d) "%s"
+  ["line"]=>
+  int(3)
+}
+called

Zend/tests/closure_const_expr/class_const.phpt

@@ -0,0 +1,25 @@
+--TEST--
+Allow defining Closures in class constants.
+--FILE--
+<?php
+
+class C {
+    const Closure = static function () {
+        echo "called", PHP_EOL;
+    };
+}
+
+var_dump(C::Closure);
+(C::Closure)();
+
+?>
+--EXPECTF--
+object(Closure)#%d (3) {
+  ["name"]=>
+  string(%d) "{closure:%s:%d}"
+  ["file"]=>
+  string(%d) "%s"
+  ["line"]=>
+  int(4)
+}
+called

Zend/tests/closure_const_expr/complex_array.phpt

@@ -0,0 +1,41 @@
+--TEST--
+Allow defining Closures wrapped in an array in const expressions.
+--FILE--
+<?php
+
+const Closure = [static function () {
+    echo "called", PHP_EOL;
+}, static function () {
+    echo "also called", PHP_EOL;
+}];
+
+var_dump(Closure);
+
+foreach (Closure as $closure) {
+    $closure();
+}
+
+?>
+--EXPECTF--
+array(2) {
+  [0]=>
+  object(Closure)#%d (3) {
+    ["name"]=>
+    string(%d) "{closure:%s:%d}"
+    ["file"]=>
+    string(%d) "%s"
+    ["line"]=>
+    int(3)
+  }
+  [1]=>
+  object(Closure)#%d (3) {
+    ["name"]=>
+    string(%d) "{closure:%s:%d}"
+    ["file"]=>
+    string(%d) "%s"
+    ["line"]=>
+    int(5)
+  }
+}
+called
+also called

Zend/tests/closure_const_expr/complex_new.phpt

@@ -0,0 +1,33 @@
+--TEST--
+Allow defining Closures passed as constructor arguments in const expressions.
+--FILE--
+<?php
+
+class Dummy {
+  public function __construct(
+      public Closure $c,
+  ) {}
+}
+
+const Closure = new Dummy(static function () {
+  echo "called", PHP_EOL;
+});
+
+var_dump(Closure);
+
+(Closure->c)();
+
+?>
+--EXPECTF--
+object(Dummy)#%d (1) {
+  ["c"]=>
+  object(Closure)#%d (3) {
+    ["name"]=>
+    string(%d) "{closure:%s:%d}"
+    ["file"]=>
+    string(%d) "%s"
+    ["line"]=>
+    int(9)
+  }
+}
+called

Zend/tests/closure_const_expr/default_args.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Closures in default argument
+--FILE--
+<?php
+
+function test(
+    Closure $name = static function () {
+        echo "default", PHP_EOL;
+    },
+) {
+    $name();
+}
+
+test();
+test(function () {
+    echo "explicit", PHP_EOL;
+});
+
+?>
+--EXPECT--
+default
+explicit

Zend/tests/closure_const_expr/disallows_non_static.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Disallows using non-static closures.
+--FILE--
+<?php
+
+class C {
+    public Closure $d = function () {
+        var_dump($this);
+    };
+}
+
+$foo = new C();
+var_dump($foo->d);
+($foo->d)();
+
+?>
+--EXPECTF--
+Fatal error: Closures in constant expressions must be static in %s on line %d

Zend/tests/closure_const_expr/disallows_using_variables.phpt

@@ -0,0 +1,17 @@
+--TEST--
+Disallows using variables.
+--FILE--
+<?php
+
+$foo = "bar";
+
+const Closure = static function () use ($foo) {
+    echo $foo, PHP_EOL;
+};
+
+var_dump(Closure);
+(Closure)();
+
+?>
+--EXPECTF--
+Fatal error: Cannot use(...) variables in constant expression in %s on line %d

Zend/tests/closure_const_expr/property_initializer.phpt

@@ -0,0 +1,27 @@
+--TEST--
+Closure in property initializer
+--FILE--
+<?php
+
+class C {
+    public Closure $d = static function () {
+        echo "called", PHP_EOL;
+    };
+}
+
+$c = new C();
+var_dump($c->d);
+($c->d)();
+
+
+?>
+--EXPECTF--
+object(Closure)#%d (3) {
+  ["name"]=>
+  string(%d) "{closure:%s:%d}"
+  ["file"]=>
+  string(%d) "%s"
+  ["line"]=>
+  int(4)
+}
+called