Fix "implicitely nullable type" warnings

See https://wiki.php.net/rfc/deprecate-implicitly-nullable-types

ChangeLog.md

@@ -3,6 +3,13 @@ XP Compiler ChangeLog
 
 ## ?.?.? / ????-??-??
 
+## 8.17.2 / 2024-03-23
+
+* Fixed *implicitely nullable type* warnings for parameters with non-
+  constant expressions (e.g. `$param= new Handle(0)`) in PHP 8.4, see
+  https://wiki.php.net/rfc/deprecate-implicitly-nullable-types
+  (@thekid)
+
 ## 8.17.1 / 2024-01-06
 
 * Fixed emitting captures and return types for closures - @thekid

src/main/php/lang/ast/emit/PHP.class.php

@@ -297,24 +297,35 @@ protected function emitArray($result, $array) {
   }
 
   protected function emitParameter($result, $parameter) {
+    $result->locals[$parameter->name]= true;
     $parameter->annotations && $this->emitOne($result, $parameter->annotations);
-    if ($parameter->type && $t= $this->literal($parameter->type)) {
-      $result->out->write($t.' ');
+
+    // If we have a non-constant default and a type, emit a nullable type hint
+    // to prevent "implicitely nullable type" warnings being raised. See here:
+    // https://wiki.php.net/rfc/deprecate-implicitly-nullable-types
+    $type= $parameter->type;
+    if ($parameter->default) {
+      $const= $this->isConstant($result, $parameter->default);
+      if ($type && !$const && !$type instanceof IsNullable) {
+        $type= new IsNullable($parameter->type);
+      }
     }
+    if ($type && $t= $this->literal($type)) $result->out->write($t.' ');
+
     if ($parameter->variadic) {
       $result->out->write('... $'.$parameter->name);
     } else {
       $result->out->write(($parameter->reference ? '&' : '').'$'.$parameter->name);
     }
+
     if ($parameter->default) {
-      if ($this->isConstant($result, $parameter->default)) {
+      if ($const) {
         $result->out->write('=');
         $this->emitOne($result, $parameter->default);
       } else {
         $result->out->write('=null');
       }
     }
-    $result->locals[$parameter->name]= true;
   }
 
   protected function emitSignature($result, $signature, $use= null) {