Implement ??= operator

Zend/tests/assign_coalesce_001.phpt

@@ -0,0 +1,127 @@
+--TEST--
+Coalesce assign (??=): Basic behavior
+--FILE--
+<?php
+
+// Refcounted values
+$foo = "fo";
+$foo .= "o";
+$bar = "ba";
+$bar .= "r";
+
+// Identity function used to track single-evaluation
+function id($arg) {
+    echo "id($arg)\n";
+    return $arg;
+}
+
+echo "Simple variables:\n";
+$a = 123;
+$a ??= 456;
+var_dump($a);
+
+$b = null;
+$b ??= $foo;
+var_dump($b);
+
+$c = $foo;
+$c ??= $bar;
+var_dump($c);
+
+$d ??= $foo;
+var_dump($c);
+
+echo "\nArrays:\n";
+$ary = [];
+$ary["foo"] ??= 123;
+$ary[$foo] ??= $bar;
+$ary[$bar] ??= $foo;
+var_dump($ary);
+
+$ary = [];
+$ary[id($foo)] ??= 123;
+$ary[id($foo)] ??= $bar;
+$ary[id($bar)] ??= $foo;
+var_dump($ary);
+
+echo "\nObjects:\n";
+$obj = new stdClass;
+$obj->foo ??= 123;
+$obj->$foo ??= $bar;
+$obj->$bar ??= $foo;
+var_dump($obj);
+
+$obj = new stdClass;
+$obj->{id($foo)} ??= 123;
+$obj->{id($foo)} ??= $bar;
+$obj->{id($bar)} ??= $foo;
+var_dump($obj);
+
+class Test {
+    public static $foo;
+    public static $bar;
+}
+
+echo "\nStatic props:\n";
+Test::$foo ??= 123;
+Test::$$foo ??= $bar;
+Test::$$bar ??= $foo;
+var_dump(Test::$foo, Test::$bar);
+
+Test::$foo = null;
+Test::$bar = null;
+Test::${id($foo)} ??= 123;
+Test::${id($foo)} ??= $bar;
+Test::${id($bar)} ??= $foo;
+var_dump(Test::$foo, Test::$bar);
+
+?>
+--EXPECT--
+Simple variables:
+int(123)
+string(3) "foo"
+string(3) "foo"
+string(3) "foo"
+
+Arrays:
+array(2) {
+  ["foo"]=>
+  int(123)
+  ["bar"]=>
+  string(3) "foo"
+}
+id(foo)
+id(foo)
+id(bar)
+array(2) {
+  ["foo"]=>
+  int(123)
+  ["bar"]=>
+  string(3) "foo"
+}
+
+Objects:
+object(stdClass)#1 (2) {
+  ["foo"]=>
+  int(123)
+  ["bar"]=>
+  string(3) "foo"
+}
+id(foo)
+id(foo)
+id(bar)
+object(stdClass)#2 (2) {
+  ["foo"]=>
+  int(123)
+  ["bar"]=>
+  string(3) "foo"
+}
+
+Static props:
+int(123)
+string(3) "foo"
+id(foo)
+id(foo)
+id(bar)
+int(123)
+string(3) "foo"

Zend/tests/assign_coalesce_002.phpt

@@ -0,0 +1,84 @@
+--TEST--
+Coalesce assign (??=): Exception handling
+--FILE--
+<?php
+
+$foo = "fo";
+$foo .= "o";
+$bar = "ba";
+$bar .= "r";
+
+function id($arg) {
+    echo "id($arg)\n";
+    return $arg;
+}
+
+function do_throw($msg) {
+    throw new Exception($msg);
+}
+
+$ary = [];
+try {
+    $ary[id($foo)] ??= do_throw("ex1");
+} catch (Exception $e) {
+    echo $e->getMessage(), "\n";
+}
+var_dump($ary);
+
+class AA implements ArrayAccess {
+    public function offsetExists($k) {
+        return true;
+    }
+    public function &offsetGet($k) {
+        $var = ["foo" => "bar"];
+        return $var;
+    }
+    public function offsetSet($k,$v) {}
+    public function offsetUnset($k) {}
+}
+
+class Dtor {
+    public function __destruct() {
+        throw new Exception("dtor");
+    }
+}
+
+$ary = new AA;
+try {
+    $ary[new Dtor][id($foo)] ??= $bar;
+} catch (Exception $e) {
+    echo $e->getMessage(), "\n";
+}
+var_dump($foo);
+
+class AA2 implements ArrayAccess {
+    public function offsetExists($k) {
+        return false;
+    }
+    public function offsetGet($k) {
+        return null;
+    }
+    public function offsetSet($k,$v) {}
+    public function offsetUnset($k) {}
+}
+
+$ary = ["foo" => new AA2];
+try {
+    $ary[id($foo)][new Dtor] ??= $bar;
+} catch (Exception $e) {
+    echo $e->getMessage(), "\n";
+}
+var_dump($foo);
+
+?>
+--EXPECT--
+id(foo)
+ex1
+array(0) {
+}
+id(foo)
+dtor
+string(3) "foo"
+id(foo)
+dtor
+string(3) "foo"

Zend/tests/assign_coalesce_003.phpt

@@ -0,0 +1,70 @@
+--TEST--
+Coalesce assign (??=): ArrayAccess handling
+--FILE--
+<?php
+
+function id($arg) {
+    echo "id($arg)\n";
+    return $arg;
+}
+
+class AA implements ArrayAccess {
+    public $data;
+    public function __construct($data = []) {
+        $this->data = $data;
+    }
+    public function &offsetGet($k) {
+        echo "offsetGet($k)\n";
+        return $this->data[$k];
+    }
+    public function offsetExists($k) {
+        echo "offsetExists($k)\n";
+        return array_key_exists($k, $this->data);
+    }
+    public function offsetSet($k,$v) {
+        echo "offsetSet($k,$v)\n";
+        $this->data[$k] = $v;
+    }
+    public function offsetUnset($k) { }
+}
+
+$ary = new AA(["foo" => new AA, "null" => null]);
+
+echo "[foo]\n";
+$ary["foo"] ??= "bar";
+
+echo "[bar]\n";
+$ary["bar"] ??= "foo";
+
+echo "[null]\n";
+$ary["null"] ??= "baz";
+
+echo "[foo][bar]\n";
+$ary["foo"]["bar"] ??= "abc";
+
+echo "[foo][bar]\n";
+$ary["foo"]["bar"] ??= "def";
+
+?>
+--EXPECT--
+[foo]
+offsetExists(foo)
+offsetGet(foo)
+[bar]
+offsetExists(bar)
+offsetSet(bar,foo)
+[null]
+offsetExists(null)
+offsetGet(null)
+offsetSet(null,baz)
+[foo][bar]
+offsetExists(foo)
+offsetGet(foo)
+offsetExists(bar)
+offsetGet(foo)
+offsetSet(bar,abc)
+[foo][bar]
+offsetExists(foo)
+offsetGet(foo)
+offsetExists(bar)
+offsetGet(bar)

Zend/tests/assign_coalesce_004.phpt

@@ -0,0 +1,11 @@
+--TEST--
+Coalesce assign (??=): Non-writable variable
+--FILE--
+<?php
+
+function foo() { return 123; }
+foo() ??= 456;
+
+?>
+--EXPECTF--
+Fatal error: Can't use function return value in write context in %s on line %d

Zend/tests/assign_coalesce_005.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Coalesce assign (??=): Cannot reassign $this
+--FILE--
+<?php
+
+class Test {
+    public function foobar() {
+        $this ??= 123;
+    }
+}
+
+?>
+--EXPECTF--
+Fatal error: Cannot re-assign $this in %s on line %d

Zend/zend_ast.c

@@ -1672,6 +1672,7 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 				EMPTY_SWITCH_DEFAULT_CASE();
 			}
 			break;
+		case ZEND_AST_ASSIGN_COALESCE: BINARY_OP(" \?\?= ", 90, 91, 90);
 		case ZEND_AST_BINARY_OP:
 			switch (ast->attr) {
 				case ZEND_ADD:                 BINARY_OP(" + ",   200, 200, 201);

Zend/zend_ast.h

@@ -120,6 +120,7 @@ enum _zend_ast_kind {
 	ZEND_AST_INSTANCEOF,
 	ZEND_AST_YIELD,
 	ZEND_AST_COALESCE,
+	ZEND_AST_ASSIGN_COALESCE,
 
 	ZEND_AST_STATIC,
 	ZEND_AST_WHILE,