[feature/twig] New Twig filter, subset

This filter grabs a subset of a loop for output (according to past
functionality).

PHPBB3-11598

phpBB/includes/template/twig/extension.php

@@ -35,12 +35,19 @@ class phpbb_template_twig_extension extends Twig_Extension
 		);
 	}
 
+    public function getFilters()
+    {
+        return array(
+            new Twig_SimpleFilter('subset', array($this, 'loop_subset'), array('needs_environment' => true)),
+		);
+    }
+
 	public function getOperators()
 	{
 		return array(
 			array(),
 			array(
-				// @todo check if all these are needed (or others)
+				// @todo check if all these are needed (or others) and set precedence correctly
 				'eq' => array('precedence' => 20, 'class' => 'Twig_Node_Expression_Binary_Equal', 'associativity' => Twig_ExpressionParser::OPERATOR_LEFT),
 
 				'ne' => array('precedence' => 20, 'class' => 'Twig_Node_Expression_Binary_NotEqual', 'associativity' => Twig_ExpressionParser::OPERATOR_LEFT),
@@ -60,4 +67,35 @@ class phpbb_template_twig_extension extends Twig_Extension
 			),
 		);
 	}
+
+	/**
+	 * Grabs a subset of a loop
+	 *
+	 * @param Twig_Environment $env          A Twig_Environment instance
+	 * @param mixed            $item         A variable
+	 * @param integer          $start        Start of the subset
+	 * @param integer          $end   	     End of the subset
+	 * @param Boolean          $preserveKeys Whether to preserve key or not (when the input is an array)
+	 *
+	 * @return mixed The sliced variable
+	 */
+	function loop_subset(Twig_Environment $env, $item, $start, $end = null, $preserveKeys = false)
+	{
+		// We do almost the same thing as array_slice, except when $end is positive
+		if ($end >= 1)
+		{
+			// When end is > 1, subset will end on the last item in an array with the specified $end
+			// This is different from slice in that it is the number we end on rather than the number
+			//	of items to grab (length)
+
+			// Start must always be the actual starting number for this calculation (not negative)
+			$start = ($start < 0) ? sizeof($item) + $start : $start;
+			$end = $end - $start;
+		}
+
+		// We always include the last element (this was the past design)
+		$end = ($end == -1 || $end === null) ? null : $end + 1;
+
+		return twig_slice($env, $item, $start, $end, $preserveKeys);
+	}
 }

phpBB/includes/template/twig/lexer.php

@@ -78,7 +78,7 @@ class phpbb_template_twig_lexer extends Twig_Lexer
 		$callback = function ($matches) use ($parent_class, $parent_nodes)
 		{
 			$name = $matches[1];
-			$slice = $matches[2];
+			$subset = trim(substr($matches[2], 1, -1)); // Remove parenthesis
 			$body = $matches[3];
 
 			// Is the designer wanting to call another loop in a loop?
@@ -118,16 +118,19 @@ class phpbb_template_twig_lexer extends Twig_Lexer
 			array_pop($parent_nodes);
 			$parent = (!empty($parent_nodes)) ? end($parent_nodes) . '_loop_element.' : '';
 
-			$slice = ($slice) ? '|slice(' . $slice . ')' : '';
+			if ($subset !== '')
+			{
+				$subset = '|subset(' . $subset . ')';
+			}
 
 			// Turn into a Twig for loop, using (loop name)_loop_element for each child
-			return "{% for {$name}_loop_element in {$parent}{$name}{$slice} %}{$body}{% endfor %}";
+			return "{% for {$name}_loop_element in {$parent}{$name}{$subset} %}{$body}{% endfor %}";
 		};
 
 		// Replace <!-- BEGINELSE --> correctly, only needs to be done once
 		$code = str_replace('<!-- BEGINELSE -->', '{% else %}', $code);
 
-		return preg_replace_callback('#<!-- BEGIN ([!a-zA-Z0-9_]+)\(?([0-9,]+)?\)? -->(.+?)<!-- END \1 -->#s', $callback, $code);
+		return preg_replace_callback('#<!-- BEGIN ([!a-zA-Z0-9_]+)(\([0-9,\-]+\))? -->(.+?)<!-- END \1 -->#s', $callback, $code);
 	}
 
 	/**