[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    ";
}

[stof]

Restricting the type is a BC break. You should introduce the new class in 3.x with a deprecation instead (where passing something else than a ForElseNode or null would trigger a deprecation and wrap the node in a ForElseNode, using the line of that node as fallback line number)

[ruudk]

Sounds like a good idea.

Do you think the direction of this PR is OK / makes sense? I can propose the V3 change once that is clear.

[fabpot]

IIUC, this is to get the // line xxx comment above the if instead of inside it, right?

What about adding ->addDebugInfo($this->getNode('else')) after current line 75 instead?

[ruudk]

The goal of this PR is to get the line number of {% else %} above the PHP if condition.

Your suggestion would print the line number of the line after the {% else %}.

[ruudk]

You can see it in the example of the PR description.

[fabpot]

I might be missing something. Isn't it what you want?

$_v0 = new \Twig\Runtime\LoopIterator([1, 2, 3, 4]);
yield from ($_v1 = function ($iterator, &$context, $blocks, $recurseFunc, $depth) {
    $macros = $this->macros;
    $parent = $context;
    foreach ($iterator as $context["_key"] => $context["key"]) {
        // line 3
        yield "    IF";
    }
    // line 5
    if (0 === $iterator->getIndex0()) {
        yield "    ELSE";
    }
    unset($context['_key'], $context['key']);
    $context = array_intersect_key($context, $parent) + $parent;
    yield from [];
})($_v0, $context, $blocks, $_v1, 0);

[ruudk]

I tried doing ->addDebugInfo($this->getNode('else')) but that will print the wrong line (4 instead of 3).

1 {% for product in products %}
2    <h2>FOR</h2>
3 {% else %}
4    <p>No products found</p>
5 {% endfor %}

Before this PR it compiles to:

// 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 PR it compiles to:

// 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    ";
}

Because if (!$context['_iterated']) { points to {% else %} on line 3.