[Twig 4] Introduce ForElseNode

[ruudk]

Currently there is no line number information for {% else %} inside a for loop.

Normally, this wouldn't be such a big deal.

But TwigStan uses this line information to map errors in PHP back to the original Twig source.

Let's say you have the following template:

{% for product in products %}
    <h2>FOR</h2>
{% else %}
    <p>No products found</p>
{% endfor %}

And products is of type non-empty-array<Product>, it means that the else will never happen.

This is currently reported as:

Negated boolean expression is always false.
🔖 booleanNot.alwaysFalse
🐘 compiled_index.php:83
🌱 templates/product/index.html.twig:2
🎯 src/Controller/ProductController.php:15

But as you can see, it points to line number 2, instead of line number 3.

In the compiled code, it looks like this:

// line 1
foreach ($context['_seq'] as $context["_key"] => $context["product"]) {
    // line 2
    yield "        <h2>FOR</h2>\n    ";
    $context['_iterated'] = \true;
}
if (!$context['_iterated']) {
    // line 4
    yield "        <p>No products found</p>\n    ";
}

With this change, we will change the compiled code to become:

// line 1
foreach ($context['_seq'] as $context["_key"] => $context["product"]) {
    // line 2
    yield "        <h2>FOR</h2>\n    ";
    $context['_iterated'] = \true;
}
// line 3
if (!$context['_iterated']) {
    // line 4
    yield "        <p>No products found</p>\n    ";
}

[fabpot]

@ruudk I've done the work here for 3.x: #4553

[ruudk]

Thank you! I will rebase as soon as V4 is synced.

[ruudk]

I guess this was closed accidentally?

[ruudk]

Ah, it's already merged.

[fabpot]

Ah, it's already merged.

Yes, I made the needed changes when merging 3.x to 4.x (basically resolving the conflicts).

[ruudk]

Got it, thank you for getting this merged 💙