[TwigComponent] Fix opening of default block inside an open twig block

[sneakyvv]

Q	A
Bug fix?	yes
New feature?	no
Tickets
License	MIT

Symptom

SyntaxError when using a Embedded Component inside a block

A template that extends another one cannot include content outside Twig blocks. Did you forget to put the content inside a {% block %} tag?

Reproduce

Embed a component inside a twig block.

<twig:Foo>
    <twig:block name="foo_block">
        <twig:Foo>
            <twig:Foo />
        </twig:Foo>
    </twig:block>
</twig:Foo>

Problem

This currently renders to

{% component 'Foo' %}
    {% block foo_block %}
        {% component 'Foo' %}
            {{ component('Foo') }}
        {% endcomponent %}
    {% endblock %}
{% endcomponent %}

The last {{ component('Foo') }} should be enclosed within a content block.

Note: the error won't happen if another non-whitespace character is used before the last <twig:Foo />, because then the transformed output contains a content block for that. It ony happens when lexing a twig block with a component inside which immediately has another component inside it.

Cause

https://github.com/symfony/ux/blob/2.x/src/TwigComponent/src/Twig/TwigPreLexer.php#L82-L89 checks imo incorrectly whether it's inside a block already. As long as a new component is being processed it's OK to open a new default content block. (see solution)

Solution

This PR will lex the above twig syntax to:

{% component 'Foo' %}
    {% block foo_block %}
        {% component 'Foo' %}
            {% block content %}{{ component('Foo') }}{% endblock %}
        {% endcomponent %}
    {% endblock %}
{% endcomponent %}

Even a content block inside a content block is still OK, because the block is part of another component's template.

<twig:Foo>
    foo_content
    <twig:block name="foo_block">
        <twig:Foo>
            <twig:Foo />
        </twig:Foo>
    </twig:block>
</twig:Foo>

{% component 'Foo' %}
    {% block content %}foo_content{% endblock %}
    {% block foo_block %}
        {% component 'Foo' %}
            {% block content %}{{ component('Foo') }}{% endblock %}
        {% endcomponent %}
    {% endblock %}
{% endcomponent %}

Note that regular block content is (still) NOT enclosed inside a default block.

<twig:Foo>
    foo_content
    <twig:block name="foo_block">
        foo_block_content
        <twig:Foo>
            <twig:Foo />
        </twig:Foo>
    </twig:block>
</twig:Foo>

{% component 'Foo' %}
    {% block content %}foo_content{% endblock %}
    {% block foo_block %}
        foo_block_content
        {% component 'Foo' %}
        {% block content %}{{ component('Foo') }}{% endblock %}
        {% endcomponent %}
    {% endblock %}
{% endcomponent %}

[sneakyvv]

@weaverryan Going to tag you here since git blame indicates you added the check at https://github.com/symfony/ux/blob/2.x/src/TwigComponent/src/Twig/TwigPreLexer.php#L82-L89. So perhaps, you can tell if I'm wrong in saying that the $insideOfBlock check shouldn't happen.

[weaverryan]

I agree it looks weird that you basically undid part of an earlier fix I did, but I wrote good test cases for that bug and you added a new test case here. So very possible I fixed my earlier bug and this code was never needed (and in the weeds, I thought it was). For this complex feature, we've gotta let the tests be our guide. Thanks!