feature #2239 Add "is defined" support for block() (hason, fabpot)

This PR was merged into the 1.x branch.

Discussion
----------

Add "is defined" support for block()

replaces #1831, fixes #1821

I think reusing the semantic of the `defined` test is more idiomatic and easily discoverable.

/cc @hason

Commits
-------

3ce06af added 'is defined' support for block()
4f013e0 Add test to check if a block exists

CHANGELOG

@@ -1,5 +1,6 @@
 * 1.28.0 (2016-XX-XX)
 
+ * added "is defined" support for block()
  * optimized the way attributes are fetched
 
 * 1.27.0 (2016-10-25)

doc/functions/block.rst

@@ -12,4 +12,13 @@ times, use the ``block`` function:
 
     {% block body %}{% endblock %}
 
+Use the ``defined`` test to check if a block exists in the context of the
+current template:
+
+.. code-block:: jinja
+
+    {% if block("footer") is defined %}
+        ...
+    {% endif %}
+
 .. seealso:: :doc:`extends<../tags/extends>`, :doc:`parent<../functions/parent>`

lib/Twig/Node/Expression/BlockReference.php

@@ -26,24 +26,32 @@ class Twig_Node_Expression_BlockReference extends Twig_Node_Expression
             $tag = func_num_args() > 3 ? func_get_arg(3) : null;
         }
 
-        parent::__construct(array('name' => $name), array('output' => false), $lineno, $tag);
+        parent::__construct(array('name' => $name), array('is_defined_test' => false, 'output' => false), $lineno, $tag);
     }
 
     public function compile(Twig_Compiler $compiler)
     {
-        if ($this->getAttribute('output')) {
+        if ($this->getAttribute('is_defined_test')) {
             $compiler
-                ->addDebugInfo($this)
-                ->write('$this->displayBlock(')
-                ->subcompile($this->getNode('name'))
-                ->raw(", \$context, \$blocks);\n")
-            ;
-        } else {
-            $compiler
-                ->raw('$this->renderBlock(')
+                ->raw('$this->blockExists(')
                 ->subcompile($this->getNode('name'))
                 ->raw(', $context, $blocks)')
             ;
+        } else {
+            if ($this->getAttribute('output')) {
+                $compiler
+                    ->addDebugInfo($this)
+                    ->write('$this->displayBlock(')
+                    ->subcompile($this->getNode('name'))
+                    ->raw(", \$context, \$blocks);\n")
+                ;
+            } else {
+                $compiler
+                    ->raw('$this->renderBlock(')
+                    ->subcompile($this->getNode('name'))
+                    ->raw(', $context, $blocks)')
+                ;
+            }
         }
     }
 }

lib/Twig/Node/Expression/Test/Defined.php

@@ -29,8 +29,9 @@ class Twig_Node_Expression_Test_Defined extends Twig_Node_Expression_Test
             $node->setAttribute('is_defined_test', true);
         } elseif ($node instanceof Twig_Node_Expression_GetAttr) {
             $node->setAttribute('is_defined_test', true);
-
             $this->changeIgnoreStrictCheck($node);
+        } elseif ($node instanceof Twig_Node_Expression_BlockReference) {
+            $node->setAttribute('is_defined_test', true);
         } elseif ($node instanceof Twig_Node_Expression_Constant || $node instanceof Twig_Node_Expression_Array) {
             $node = new Twig_Node_Expression_Constant(true, $node->getTemplateLine());
         } else {

lib/Twig/Template.php

@@ -286,6 +286,8 @@ abstract class Twig_Template implements Twig_TemplateInterface
      *
      * @return bool true if the block exists, false otherwise
      *
+     * @see blockExists
+     *
      * @internal
      */
     public function hasBlock($name)
@@ -653,4 +655,37 @@ abstract class Twig_Template implements Twig_TemplateInterface
 
         return $ret;
     }
+
+    /**
+     * Returns whether a block exists or not in the current context of the template.
+     *
+     * This method checks blocks defined in the current template
+     * or defined in "used" traits or defined in parent templates.
+     *
+     * @param string $name    The block name
+     * @param array  $context The context
+     * @param array  $blocks  The current set of blocks
+     *
+     * @return bool true if the block exists, false otherwise
+     *
+     * @see hasBlock
+     *
+     * @internal
+     */
+    protected function blockExists($name, array $context, array $blocks = array())
+    {
+        if (isset($blocks[$name])) {
+            return $blocks[$name][0] instanceof self;
+        }
+
+        if (isset($this->blocks[$name])) {
+            return true;
+        }
+
+        if (false !== $parent = $this->getParent($context)) {
+            return $parent->blockExists($name, $context);
+        }
+
+        return false;
+    }
 }

test/Twig/Tests/Fixtures/tests/defined_for_blocks.test

@@ -0,0 +1,38 @@
+--TEST--
+"defined" support for blocks
+--TEMPLATE--
+{% extends 'parent' %}
+{% block icon %}icon{% endblock %}
+{% block body %}
+    {{ parent() }}
+    {{ block('foo') is defined ? 'ok' : 'ko' }}
+    {{ block('footer') is defined ? 'ok' : 'ko' }}
+    {{ block('icon') is defined ? 'ok' : 'ko' }}
+    {{ block('block1') is defined ? 'ok' : 'ko' }}
+    {%- embed 'embed' %}
+        {% block content %}content{% endblock %}
+    {% endembed %}
+{% endblock %}
+{% use 'blocks' %}
+--TEMPLATE(parent)--
+{% block body %}
+  {{ block('icon') is defined ? 'ok' : 'ko' -}}
+{% endblock %}
+{% block footer %}{% endblock %}
+--TEMPLATE(embed)--
+{{ block('icon') is defined ? 'ok' : 'ko' }}
+{{ block('content') is defined ? 'ok' : 'ko' }}
+{{ block('block1') is defined ? 'ok' : 'ko' }}
+--TEMPLATE(blocks)--
+{% block block1 %}{%endblock %}
+--DATA--
+return array()
+--EXPECT--
+ok
+    ko
+    ok
+    ok
+    ok
+ko
+ok
+ko