Refactor frontmatter to no longer use decorations API

src/main/php/web/frontend/TemplateParser.class.php

@@ -42,9 +42,10 @@ public function parse(Tokenizer $tokens, $start= '{{', $end= '}}', $indent= '')
       }
 
       $tokens->nextToken("\n");
-      $nodes= parent::parse($tokens, $start, $end, $indent);
-      $nodes->decorate(new FrontMatter((self::$yaml ?? self::$yaml= new YamlParser())->parse(new StringInput($yaml))));
-      return $nodes;
+      return new WithFrontMatter(
+        parent::parse($tokens, $start, $end, $indent),
+        (self::$yaml ?? self::$yaml= new YamlParser())->parse(new StringInput($yaml))
+      );
     }
 
     // Just a regular template, delegate to parent

src/main/php/web/frontend/WithFrontMatter.class.php

@@ -0,0 +1,32 @@
+<?php namespace web\frontend;
+
+use com\github\mustache\Node;
+
+class WithFrontMatter extends Node {
+  private $nodes, $pairs;
+
+  /**
+   * Creates new frontmatter
+   *
+   * @param  com.handlebarsjs.Nodes $nodes
+   * @param  [:var] $pairs
+   */
+  public function __construct($nodes, $pairs) {
+    $this->nodes= $nodes;
+    $this->pairs= (array)$pairs;
+  }
+
+  /**
+   * Evaluates this node
+   *
+   * @param  com.github.mustache.Context $context the rendering context
+   * @param  io.streams.OutputStream $out
+   */
+  public function write($context, $out) {
+    $context->variables+= $this->pairs;
+    $this->nodes->write($context, $out);
+  }
+
+  /** @return string */
+  public function __toString() { return (string)$this->nodes; }
+}