feat: add null coalescing assign (#720)

src/Ast/AST.php

@@ -428,7 +428,7 @@ public function toCode(): string
                 if ($this->oneLine) {
                     $itemsStr = $items->skipLast(1)->map(fn ($x) => "{$x}, ")->join();
                     $itemsStr = $itemsStr . "{$items->last()}";
-                    return "[{$itemsStr}]";    
+                    return "[{$itemsStr}]";
                 }
                 $itemsStr = $items->map(fn ($x) => "{$x},\n")->join();
                 $firstNl = count($items) === 0 ? '' : "\n";
@@ -773,10 +773,10 @@ public function toCode(): string
 
     /**
      * Create a '??' expression.
-     * 
+     *
      * @param Expression $expr The expression to check \isset and !\is_null, as well as the value to return if true.
      * @param Expression $false The expresion to return if $expr is not set or is null.
-     * 
+     *
      * @return Expression
      */
     public static function nullCoalescing(Expression $expr, Expression $false): Expression
@@ -795,6 +795,30 @@ public function toCode(): string
         };
     }
 
+    /**
+     * Create a '??=' (noal-coalescing assignment) expression.
+     *
+     * @param AST $to Assign a value to this.
+     * @param mixed $from Assign from this.
+     *
+     * @return Expression
+     */
+    public static function nullCoalescingAssign(AST $to, $from): Expression
+    {
+        return new class($to, $from) extends Expression {
+            public function __construct($to, $from)
+            {
+                $this->to = $to;
+                $this->from = $from;
+            }
+            public function toCode(): string
+            {
+                return static::toPhp($this->to) .
+                    ' ??= ' . static::toPhp($this->from);
+            }
+        };
+    }
+
     /**
      * Create a while statement. This method returns a callable into which the loop code is passed.
      *

tests/Unit/Ast/ASTTest.php

@@ -85,4 +85,11 @@ public function testAccessSelf(): void
         $ast = AST::Access(AST::SELF, "\0property2");
         $this->assertEquals('self::property2', $ast->toCode());
     }
+
+    public function testNullCoalescingAssign(): void
+    {
+        $xIndex = AST::index(AST::var('x'), 'foo');
+        $ast = AST::nullCoalescingAssign($xIndex, 'bar');
+        $this->assertEquals("\$x['foo'] ??= 'bar'", $ast->toCode());
+    }
 }