Implement arrow functions

Per RFC: https://wiki.php.net/rfc/arrow_functions_v2

Co-authored-by: Levi Morrison <levim@php.net>
Co-authored-by: Bob Weinand <bobwei9@hotmail.com>

UPGRADING

@@ -24,6 +24,9 @@ PHP 7.4 UPGRADE NOTES
 - Core:
   . get_declared_classes() no longer returns anonymous classes that haven't
     been instantiated yet.
+  . "fn" is now a reserved keyword. In particular it can no longer be used as a
+    function or class name. It can still be used as a method or class constant
+    name.
 
 - Curl:
   . Attempting to serialize a CURLFile class will now generate an exception.
@@ -116,6 +119,14 @@ PHP 7.4 UPGRADE NOTES
     $user->name can only be assigned strings. For more information see the
     RFC: https://wiki.php.net/rfc/typed_properties_v2
 
+  . Added support for arrow functions with implicit by-value scope binding.
+    For example:
+
+        $factor = 10;
+        $nums = array_map(fn($num) => $num * $factor, $nums);
+
+    RFC: https://wiki.php.net/rfc/arrow_functions_v2
+
   . Added support for coalesce assign (??=) operator. For example:
 
         $array['key'] ??= computeDefault();

Zend/tests/arg_unpack/many_args.phpt

@@ -3,12 +3,12 @@ Argument unpacking with many arguments
 --FILE--
 <?php
 
-function fn(...$args) {
+function f(...$args) {
     var_dump(count($args));
 }
 
 $array = array_fill(0, 10000, 42);
-fn(...$array, ...$array);
+f(...$array, ...$array);
 
 ?>
 --EXPECT--

Zend/tests/arrow_functions/001.phpt

@@ -0,0 +1,45 @@
+--TEST--
+Basic arrow function functionality check
+--FILE--
+<?php
+
+$foo = fn() => 1;
+var_dump($foo());
+
+$foo = fn($x) => $x;
+var_dump($foo(2));
+
+$foo = fn($x, $y) => $x + $y;
+var_dump($foo(1, 2));
+
+// Closing over $var
+$var = 4;
+$foo = fn() => $var;
+var_dump($foo());
+
+// Not closing over $var, it's a parameter
+$foo = fn($var) => $var;
+var_dump($foo(5));
+
+// Close over $var by-value, not by-reference
+$var = 5;
+$foo = fn() => ++$var;
+var_dump($foo());
+var_dump($var);
+
+// Nested arrow functions closing over variable
+$var = 6;
+var_dump((fn() => fn() => $var)()());
+var_dump((fn() => function() use($var) { return $var; })()());
+
+?>
+--EXPECT--
+int(1)
+int(2)
+int(3)
+int(4)
+int(5)
+int(6)
+int(5)
+int(6)
+int(6)

Zend/tests/arrow_functions/002.phpt

@@ -0,0 +1,13 @@
+--TEST--
+Arrow functions implicit use must be throwing notices only upon actual use
+--FILE--
+<?php
+
+$b = 1;
+
+var_dump((fn() => $b + $c)());
+
+?>
+--EXPECTF--
+Notice: Undefined variable: c in %s on line %d
+int(1)

Zend/tests/arrow_functions/003.phpt

@@ -0,0 +1,21 @@
+--TEST--
+Variable-variables inside arrow functions
+--FILE--
+<?php
+
+$a = 1;
+$var = "a";
+$fn = fn() => $$var;
+var_dump($fn());
+
+${5} = 2;
+$fn = fn() => ${5};
+var_dump($fn());
+
+?>
+--EXPECTF--
+Notice: Undefined variable: a in %s on line %d
+NULL
+
+Notice: Undefined variable: 5 in %s on line %d
+NULL

Zend/tests/arrow_functions/004.phpt

@@ -0,0 +1,13 @@
+--TEST--
+Auto-globals in arrow functions
+--FILE--
+<?php
+
+// This should work, but *not* generate a binding for $GLOBALS
+$a = 123;
+$fn = fn() => $GLOBALS['a'];
+var_dump($fn());
+
+?>
+--EXPECT--
+int(123)

Zend/tests/arrow_functions/005.phpt

@@ -0,0 +1,54 @@
+--TEST--
+Arrow function $this binding
+--FILE--
+<?php
+
+class Test {
+    public function method() {
+        // It would be okay if this is NULL, but the rest should work
+        $fn = fn() => 42;
+        $r = new ReflectionFunction($fn);
+        var_dump($r->getClosureThis());
+
+        $fn = fn() => $this;
+        var_dump($fn());
+
+        $fn = fn() => Test::method2();
+        $fn();
+
+        $fn = fn() => call_user_func('Test::method2');
+        $fn();
+
+        $thisName = "this";
+        $fn = fn() => $$thisName;
+        var_dump($fn());
+
+        $fn = fn() => self::class;
+        var_dump($fn());
+
+        // static can be used to unbind $this
+        $fn = static fn() => isset($this);
+        var_dump($fn());
+    }
+
+    public function method2() {
+        var_dump($this);
+    }
+}
+
+(new Test)->method();
+
+?>
+--EXPECT--
+object(Test)#1 (0) {
+}
+object(Test)#1 (0) {
+}
+object(Test)#1 (0) {
+}
+object(Test)#1 (0) {
+}
+object(Test)#1 (0) {
+}
+string(4) "Test"
+bool(false)

Zend/tests/arrow_functions/006.phpt

@@ -0,0 +1,44 @@
+--TEST--
+Arrow functions syntax variations
+--FILE--
+<?php
+
+// By-reference argument and return
+$var = 1;
+$id = fn&(&$x) => $x;
+$ref =& $id($var);
+$ref++;
+var_dump($var);
+
+// int argument and return type
+$var = 10;
+$int_fn = fn(int $x): int => $x;
+var_dump($int_fn($var));
+try {
+    $int_fn("foo");
+} catch (TypeError $e) {
+    echo $e->getMessage(), "\n";
+}
+
+$varargs = fn(?int... $args): array => $args;
+var_dump($varargs(20, null, 30));
+try {
+    $varargs(40, "foo");
+} catch (TypeError $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECTF--
+int(2)
+int(10)
+Argument 1 passed to {closure}() must be of the type int, string given, called in %s on line %d
+array(3) {
+  [0]=>
+  int(20)
+  [1]=>
+  NULL
+  [2]=>
+  int(30)
+}
+Argument 2 passed to {closure}() must be of the type int or null, string given, called in %s on line %d

Zend/tests/arrow_functions/007.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Pretty printing for arrow functions
+--FILE--
+<?php
+
+// TODO We're missing parentheses for the direct call
+assert((fn() => false)());
+assert((fn&(int... $args): ?bool => $args[0])(false));
+
+?>
+--EXPECTF--
+Warning: assert(): assert(fn() => false()) failed in %s on line %d
+
+Warning: assert(): assert(fn&(int ...$args): ?bool => $args[0](false)) failed in %s on line %d

Zend/tests/arrow_functions/008.phpt

@@ -0,0 +1,28 @@
+--TEST--
+Yield inside arrow functions
+--FILE--
+<?php
+
+// This doesn't make terribly much sense, but it works...
+
+$fn = fn() => yield 123;
+foreach ($fn() as $val) {
+    var_dump($val);
+}
+
+$fn = fn() => yield from [456, 789];
+foreach ($fn() as $val) {
+    var_dump($val);
+}
+
+$fn = fn() => fn() => yield 987;
+foreach ($fn()() as $val) {
+    var_dump($val);
+}
+
+?>
+--EXPECT--
+int(123)
+int(456)
+int(789)
+int(987)

Zend/tests/generators/bug65035.phpt

@@ -4,11 +4,11 @@ Bug #65035: yield / exit segfault
 <?php
 
 function gen() {
-    fn();
+    f();
     yield;
 }
 
-function fn() {
+function f() {
     exit('Done');
 }
 

Zend/tests/grammar/semi_reserved_001.phpt

@@ -56,6 +56,7 @@ class Obj
     function switch(){ echo __METHOD__, PHP_EOL; }
     function yield(){ echo __METHOD__, PHP_EOL; }
     function function(){ echo __METHOD__, PHP_EOL; }
+    function fn(){ echo __METHOD__, PHP_EOL; }
     function if(){ echo __METHOD__, PHP_EOL; }
     function endswitch(){ echo __METHOD__, PHP_EOL; }
     function finally(){ echo __METHOD__, PHP_EOL; }
@@ -135,6 +136,7 @@ $obj->continue();
 $obj->switch();
 $obj->yield();
 $obj->function();
+$obj->fn();
 $obj->if();
 $obj->endswitch();
 $obj->finally();
@@ -213,6 +215,7 @@ Obj::continue
 Obj::switch
 Obj::yield
 Obj::function
+Obj::fn
 Obj::if
 Obj::endswitch
 Obj::finally

Zend/tests/grammar/semi_reserved_002.phpt

@@ -56,6 +56,7 @@ class Obj
     static function switch(){ echo __METHOD__, PHP_EOL; }
     static function yield(){ echo __METHOD__, PHP_EOL; }
     static function function(){ echo __METHOD__, PHP_EOL; }
+    static function fn(){ echo __METHOD__, PHP_EOL; }
     static function if(){ echo __METHOD__, PHP_EOL; }
     static function endswitch(){ echo __METHOD__, PHP_EOL; }
     static function finally(){ echo __METHOD__, PHP_EOL; }
@@ -133,6 +134,7 @@ Obj::continue();
 Obj::switch();
 Obj::yield();
 Obj::function();
+Obj::fn();
 Obj::if();
 Obj::endswitch();
 Obj::finally();
@@ -211,6 +213,7 @@ Obj::continue
 Obj::switch
 Obj::yield
 Obj::function
+Obj::fn
 Obj::if
 Obj::endswitch
 Obj::finally

Zend/tests/grammar/semi_reserved_003.phpt

@@ -56,6 +56,7 @@ class Obj
     var $switch = 'switch';
     var $yield = 'yield';
     var $function = 'function';
+    var $fn = 'fn';
     var $if = 'if';
     var $endswitch = 'endswitch';
     var $finally = 'finally';
@@ -136,6 +137,7 @@ echo $obj->continue, PHP_EOL;
 echo $obj->switch, PHP_EOL;
 echo $obj->yield, PHP_EOL;
 echo $obj->function, PHP_EOL;
+echo $obj->fn, PHP_EOL;
 echo $obj->if, PHP_EOL;
 echo $obj->endswitch, PHP_EOL;
 echo $obj->finally, PHP_EOL;
@@ -217,6 +219,7 @@ continue
 switch
 yield
 function
+fn
 if
 endswitch
 finally

Zend/tests/grammar/semi_reserved_004.phpt

@@ -56,6 +56,7 @@ class Obj
     static $switch = 'switch';
     static $yield = 'yield';
     static $function = 'function';
+    static $fn = 'fn';
     static $if = 'if';
     static $endswitch = 'endswitch';
     static $finally = 'finally';
@@ -134,6 +135,7 @@ echo Obj::$continue, PHP_EOL;
 echo Obj::$switch, PHP_EOL;
 echo Obj::$yield, PHP_EOL;
 echo Obj::$function, PHP_EOL;
+echo Obj::$fn, PHP_EOL;
 echo Obj::$if, PHP_EOL;
 echo Obj::$endswitch, PHP_EOL;
 echo Obj::$finally, PHP_EOL;
@@ -213,6 +215,7 @@ continue
 switch
 yield
 function
+fn
 if
 endswitch
 finally