Throw deprecation notice about unregistered functions without changing the compilation flow

libs/sysplugins/smarty_internal_templatecompilerbase.php

@@ -640,17 +640,18 @@ public function compilePHPFunctionCall($name, $parameter)
                         return $func_name . '(' . $parameter[ 0 ] . ')';
                     }
                 } else {
-					$first_param = array_shift($parameter);
-					$modifier = array_merge(array($name), $parameter);
-					// Now, compile the function call as a modifier
-					return $this->compileTag(
-						'private_modifier',
-						array(),
-						array(
-							'modifierlist' => array($modifier),
-							'value'        => $first_param
-						)
-					);
+
+					if (
+						!$this->smarty->loadPlugin('smarty_modifiercompiler_' . $name)
+						&& !isset($this->smarty->registered_plugins[Smarty::PLUGIN_MODIFIER][$name])
+						&& !in_array($name, ['time', 'join', 'is_array', 'in_array'])
+					) {
+						trigger_error('Using unregistered function "' . $name . '" in a template is deprecated and will be ' .
+							'removed in a future release. Use Smarty::registerPlugin to explicitly register ' .
+							'a custom modifier.', E_USER_DEPRECATED);
+					}
+
+					return $name . '(' . implode(',', $parameter) . ')';
                 }
             } else {
                 $this->trigger_template_error("unknown function '{$name}'");

tests/UnitTests/TemplateSource/_Issues/ArgumentMustBePassedByReference961Test.php

@@ -0,0 +1,67 @@
+<?php
+
+class ArgumentMustBePassedByReference961Test extends PHPUnit_Smarty
+{
+
+	/**
+	 * @group issue961
+	 */
+	public function testReset()
+	{
+		$smarty = new Smarty();
+		$smarty->registerPlugin('modifier', 'reset', 'reset');
+		$templateStr = "string:{reset(\$ar)}";
+		$smarty->assign('ar', [1,2,3]);
+		$this->assertEquals(
+			'1',
+			$smarty->fetch($templateStr)
+		);
+	}
+
+	/**
+	 * @group issue961
+	 * @deprecated
+	 */
+	public function testResetAsModifier()
+	{
+		$smarty = new Smarty();
+		try {
+			$templateStr = "string:{\$ar|reset}";
+			$smarty->assign('ar', [1,2,3]);
+			$this->assertEquals(
+				'1',
+				$smarty->fetch($templateStr)
+			);
+		} catch (Exception $e) {
+		}
+	}
+
+	/**
+	 * @group issue961
+	 */
+	public function testResetInExpression()
+	{
+		$smarty = new Smarty();
+		$smarty->registerPlugin('modifier', 'reset', 'reset');
+		$templateStr = "string:{if reset(\$ar)}ok{/if}";
+		$smarty->assign('ar', [1,2,3]);
+		$this->assertEquals(
+			'ok',
+			$smarty->fetch($templateStr)
+		);
+	}
+
+	/**
+	 * @group issue961
+	 */
+	public function testMatch()
+	{
+		$smarty = new Smarty();
+		$smarty->registerPlugin('modifier', 'preg_match', 'preg_match');
+		$templateStr = 'string:{assign var="match" value=null}{if preg_match(\'/([a-z]{4})/\', "a test", $match)}{$match.1}{/if}';
+		$this->assertEquals(
+			'test',
+			$smarty->fetch($templateStr)
+		);
+	}
+}