tweaked the error message when using extends in a block/macro

src/Parser.php

@@ -251,7 +251,7 @@ class Parser implements \Twig_ParserInterface
 
     public function peekBlockStack()
     {
-        return $this->blockStack[\count($this->blockStack) - 1];
+        return isset($this->blockStack[\count($this->blockStack) - 1]) ? $this->blockStack[\count($this->blockStack) - 1] : null;
     }
 
     public function popBlockStack()

src/TokenParser/ExtendsTokenParser.php

@@ -29,8 +29,10 @@ class ExtendsTokenParser extends AbstractTokenParser
     {
         $stream = $this->parser->getStream();
 
-        if (!$this->parser->isMainScope()) {
-            throw new SyntaxError('Cannot extend from a block.', $token->getLine(), $stream->getSourceContext());
+        if ($this->parser->peekBlockStack()) {
+            throw new SyntaxError('Cannot use "extend" in a block.', $token->getLine(), $stream->getSourceContext());
+        } elseif (!$this->parser->isMainScope()) {
+            throw new SyntaxError('Cannot use "extend" in a macro.', $token->getLine(), $stream->getSourceContext());
         }
 
         if (null !== $this->parser->getParent()) {

test/Twig/Tests/Fixtures/tags/inheritance/extends_in_block.test

@@ -0,0 +1,10 @@
+--TEST--
+"extends" tag in a block
+--TEMPLATE--
+{% block foo %}
+    {% extends "foo.twig" %}
+{% endblock %}
+--DATA--
+return []
+--EXCEPTION--
+Twig\Error\SyntaxError: Cannot use "extend" in a block in "index.twig" at line 3.

test/Twig/Tests/Fixtures/tags/inheritance/extends_in_macro.test

@@ -0,0 +1,10 @@
+--TEST--
+"extends" tag in a macro
+--TEMPLATE--
+{% macro foo() %}
+    {% extends "foo.twig" %}
+{% endmacro %}
+--DATA--
+return []
+--EXCEPTION--
+Twig\Error\SyntaxError: Cannot use "extend" in a macro in "index.twig" at line 3.

test/Twig/Tests/Fixtures/tags/inheritance/parent_in_a_block.test

@@ -1,8 +0,0 @@
---TEST--
-"extends" tag
---TEMPLATE--
-{% block content %}
-    {% extends "foo.twig" %}
-{% endblock %}
---EXCEPTION--
-Twig\Error\SyntaxError: Cannot extend from a block in "index.twig" at line 3.