Prevent notices on null to string conversion in Template::appendCode

Fixes #996

changelog/996.md

@@ -0,0 +1 @@
+- Prevent deprecation notices during compilation in PHP8.3 [#996](https://github.com/smarty-php/smarty/issues/996)

src/Compiler/Template.php

@@ -680,7 +680,8 @@ class Template extends BaseCompiler {
 	 *
 	 * @return string
 	 */
-	public function appendCode($left, $right) {
+	public function appendCode(string $left, string $right): string
+	{
 		if (preg_match('/\s*\?>\s?$/D', $left) && preg_match('/^<\?php\s+/', $right)) {
 			$left = preg_replace('/\s*\?>\s?$/D', "\n", $left);
 			$left .= preg_replace('/^<\?php\s+/', '', $right);
@@ -1056,7 +1057,7 @@ class Template extends BaseCompiler {
 		$prefixArray = array_merge($this->prefix_code, array_pop($this->prefixCodeStack));
 		$this->prefixCodeStack[] = [];
 		foreach ($prefixArray as $c) {
-			$code = $this->appendCode($code, $c);
+			$code = $this->appendCode($code, (string) $c);
 		}
 		$this->prefix_code = [];
 		return $code;

src/ParseTree/Dq.php

@@ -47,18 +47,18 @@ class Dq extends Base
             if ($subtree instanceof Code) {
                 $this->subtrees[ $last_subtree ]->data =
                     $parser->compiler->appendCode(
-                        $this->subtrees[ $last_subtree ]->data,
+                        (string) $this->subtrees[ $last_subtree ]->data,
                         '<?php echo ' . $subtree->data . ';?>'
                     );
             } elseif ($subtree instanceof DqContent) {
                 $this->subtrees[ $last_subtree ]->data =
                     $parser->compiler->appendCode(
-                        $this->subtrees[ $last_subtree ]->data,
+                        (string) $this->subtrees[ $last_subtree ]->data,
                         '<?php echo "' . $subtree->data . '";?>'
                     );
             } else {
                 $this->subtrees[ $last_subtree ]->data =
-                    $parser->compiler->appendCode($this->subtrees[ $last_subtree ]->data, $subtree->data);
+                    $parser->compiler->appendCode((string) $this->subtrees[ $last_subtree ]->data, (string) $subtree->data);
             }
         } else {
             $this->subtrees[] = $subtree;

src/ParseTree/Tag.php

@@ -62,9 +62,9 @@ class Tag extends Base
     public function assign_to_var(\Smarty\Parser\TemplateParser $parser)
     {
         $var = $parser->compiler->getNewPrefixVariable();
-        $tmp = $parser->compiler->appendCode('<?php ob_start();?>', $this->data);
+        $tmp = $parser->compiler->appendCode('<?php ob_start();?>', (string) $this->data);
         $tmp = $parser->compiler->appendCode($tmp, "<?php {$var}=ob_get_clean();?>");
-        $parser->compiler->appendPrefixCode((string) $tmp);
+        $parser->compiler->appendPrefixCode($tmp);
         return $var;
     }
 }

src/ParseTree/Template.php

@@ -114,7 +114,7 @@ class Template extends Base
                     break;
                 case 'tag':
                     foreach ($chunk['subtrees'] as $subtree) {
-                        $text = $parser->compiler->appendCode($text, $subtree->to_smarty_php($parser));
+                        $text = $parser->compiler->appendCode($text, (string) $subtree->to_smarty_php($parser));
                     }
                     $code .= $text;
                     break;

src/Parser/TemplateParser.php

@@ -2536,7 +2536,7 @@ public static $yy_action = array(
 // line 806 "src/Parser/TemplateParser.y"
     public function yy_r101(){
     $prefixVar = $this->compiler->getNewPrefixVariable();
-    $tmp = $this->compiler->appendCode('<?php ob_start();?>', $this->yystack[$this->yyidx + 0]->minor);
+    $tmp = $this->compiler->appendCode('<?php ob_start();?>', (string) $this->yystack[$this->yyidx + 0]->minor);
     $this->compiler->appendPrefixCode($this->compiler->appendCode($tmp, "<?php {$prefixVar} = ob_get_clean();?>"));
     $this->_retvalue = $prefixVar;
     }

src/Parser/TemplateParser.y

@@ -805,7 +805,7 @@ value(res)    ::= varindexed(vi) DOUBLECOLON static_class_access(r). {
                   // Smarty tag
 value(res)       ::= smartytag(st). {
     $prefixVar = $this->compiler->getNewPrefixVariable();
-    $tmp = $this->compiler->appendCode('<?php ob_start();?>', st);
+    $tmp = $this->compiler->appendCode('<?php ob_start();?>', (string) st);
     $this->compiler->appendPrefixCode($this->compiler->appendCode($tmp, "<?php {$prefixVar} = ob_get_clean();?>"));
     res = $prefixVar;
 }