Unexpected whitespace in rendered layouts when overriding Volt blocks

Answer

The Volt compiler stores the exact output of a block’s buffer, including any leading or trailing spaces, tabs, or newlines. When the overridden block contains only whitespace, inline HTML, or a conditional that evaluates to empty, that buffered whitespace is emitted in the final layout, producing visible gaps.

Confirmed facts

• Volt uses PHP output buffering to capture block contents; no automatic trimming is applied.
• This behavior has not changed between Phalcon 3.x and 4.x; the core buffering mechanism remains the same.
• Developers can control the emitted whitespace by applying the |trim filter to the block or by using Volt’s whitespace‑control delimiters ({%- and -%}) around the block.

Steps to resolve

1. Identify the overridden block in your layout template.
2. Either wrap the block content with the |trim filter:

{% block content %}{{ super() | trim }}{% endblock %}

3. Or suppress surrounding whitespace with delimiters:

{%- block content -%}{{ super() }}{%- endblock -%}

4. Re‑render the page and inspect the HTML source; the extra blank lines or spaces should disappear.

Verification (recommended)

Enable Volt’s compilation debug mode to see the generated PHP and confirm that the block buffer is used verbatim:

$volt->setOptions(['compileAlways' => true, 'stat' => true]);

Render a template with an overridden block that contains only a newline, view the source, then apply the |trim filter or delimiters and verify the whitespace is removed.