Twig Extension no longer rendering output

[tacman]

Did something change in user-defined twig extensions? This is in the category of "I swear this used to work!" My extension is at https://github.com/tacman/twig-tree-tag.

It's a slick way of making recursive calls to tree elements, like menus

    {% set food = [
        {   name: 'fruits', 
            children: [{name: 'apple'},{name:'banana'}]        },
        {   name: 'veggies',
            children: [
            {name: 'peas'},
            {name: 'carrots'}
        ]
        }
    ] %}
    <h1>Food Tree</h1>
    {% tree item in food %}
        {% if treeloop.first %}<ul>{% endif %}
        <li>
            {{ item.name }}
            {% subtree item.children|default([]) %}
        </li>
        {% if treeloop.last %}</ul>{% endif %}
    {% endtree %}

{% endblock %}

It used to display the nested HTML, and now nothing. It's registered okay, but no content either. I've created a repo showing the bug

git clone git@github.com:tacman/twig-tree-tag-demo && cd twig-tree-tag-demo
composer install
symfony server:start -d
symfony open:local

It's a trival app -- install the library, register the extesion in services.yaml, and create a controller / template.

Did something change in twig regarding output? I vaguely remember something about twig and using the output buffer in a discussion.

It's a cool tag, it really simplifies rendering trees by skipping creating a macro to make recursive calls. I didn't write it, but I did upgrade it a few years ago to Twig 3, and I'm certain at some point the twig 3 version worked.

Thanks.

[stof]

Twig has a new yield-based implementation replacing the implementation based on output buffering (which will make it compatible with Fiber-based code as it avoids the global output buffering that would be shared between fibers). Twig has a BC layer for non-yield-ready nodes. But maybe this BC layer fails to automatically handle your TreeNode logic.

[tacman]

Thanks, @stof . Is there documentation for that yet? Or a relatively simple example I can follow? I've read https://twig.symfony.com/doc/3.x/advanced.html#defining-a-node but I can't see what I'm doing differently.

Or is it something that can be fixed in the BC layer?

[fabpot]

Here is the patch you need to apply to make it work:

diff --git a/src/Twig/Node/TreeNode.php b/src/Twig/Node/TreeNode.php
index 4f5fb0d..c637bdd 100644
--- a/src/Twig/Node/TreeNode.php
+++ b/src/Twig/Node/TreeNode.php
@@ -131,7 +131,7 @@ class TreeNode extends Node
         $compiler
             ->outdent()
             ->write("};\n")
-            ->write("\$tree_")
+            ->write("yield from \$tree_")
             ->raw($this->getAttribute('as'))
             ->raw("(")
             ->subcompile($this->getNode('seq'))

You will also need to remove the usage of the twig_ensure_traversable function as it's an internal function that has been removed.

The new yield implementation BC layer has many drawbacks that were not anticipated. I need to come back to the drawing board to see how we can mitigate these problems.

[tacman]

Thanks, it's working now!

I wasn't sure how to remove the call to twig_ensure_traversable, so I replaced it with the internal call that's used elsewhere:

            ->write("\$context['_seq'] = CoreExtension::ensureTraversable(\$data);\n")

Is there a better way?

[fabpot]

ensureTraversable

That's the way to go indeed.

[tacman]

Seems to be working fine now, thanks!

[ericmorand]

@fabpot

That's the way to go indeed.

CoreExtension::ensureTraversable is internal too. How can this be the way to go if using twig_ensure_traversable, also internal, was not the way to go and was removed without notice - I quote you:

You will also need to remove the usage of the twig_ensure_traversable function as it's an internal function that has been removed.

[fabpot]

@fabpot

That's the way to go indeed.

CoreExtension::ensureTraversable is internal too. How can this be the way to go if using twig_ensure_traversable, also internal, was not the way to go and was removed without notice - I quote you:

You will also need to remove the usage of the twig_ensure_traversable function as it's an internal function that has been removed.

"The way to go" just means that CoreExtension::ensureTraversable is the replacement for twig_ensure_traversable.But to make it clear, this is still internal and not recommended for usage in user space.

[ericmorand]

@fabpot fair enough. Is there a recommended way?

[fabpot]

@fabpot fair enough. Is there a recommended way?

That's really a one liner: return is_iterable($seq) ? $seq : [];