Add an html_attr function to make outputting HTML attributes easier

CHANGELOG

@@ -3,6 +3,7 @@
  * Add support for renaming variables in object destructuring (`{name: userName} = user`)
  * Add `html_attr_relaxed` escaping strategy that preserves :, @, [, and ] for front-end framework attribute names
  * Add support for short-circuiting in null-safe operator chains
+ * Add the `html_attr` function and `html_attr_merge` as well as `html_attr_type` filters
 
 # 3.23.0 (2026-01-23)
 

doc/filters/html_attr_merge.rst

@@ -0,0 +1,141 @@
+``html_attr_merge``
+===================
+
+.. _html_attr_merge:
+
+.. versionadded:: 3.24
+
+    The ``html_attr_merge`` filter was added in Twig 3.24.
+
+The ``html_attr_merge`` filter merges multiple mappings that represent
+HTML attribute values. Such mappings contain the names of the HTML attributes
+as keys, and the corresponding values represent the attributes' values.
+
+It is primarily designed for working with arrays that are passed to the
+:ref:`html_attr` function. It closely resembles the :doc:`merge <../filters/merge>`
+filter, but has different merge behavior for values that are iterables
+themselves, as it will merge such values in turn.
+
+The filter returns a new merged array:
+
+.. code-block:: twig
+
+    {% set base = {class: ['btn'], type: 'button'} %}
+    {% set variant = {class: ['btn-primary'], disabled: true} %}
+
+    {% set merged = base|html_attr_merge(variant) %}
+
+    {# merged is now: {
+        class: ['btn', 'btn-primary'],
+        type: 'button',
+        disabled: true
+    } #}
+
+The filter accepts multiple arrays as arguments and merges them from left to right:
+
+.. code-block:: twig
+
+    {% set merged = base|html_attr_merge(variant1, variant2, variant3) %}
+
+A common use case is to build attribute mappings conditionally by merging multiple
+parts based on conditions. To make this conditional merging more convenient, filter
+arguments that are ``false``, ``null`` or empty arrays are ignored:
+
+.. code-block:: twig
+
+    {% set button_attrs = {
+        type: 'button',
+        class: ['btn']
+    }|html_attr_merge(
+        variant == 'primary' ? { class: ['btn-primary'] },
+        variant == 'secondary' ? { class: ['btn-secondary'] },
+        size == 'large' ? { class: ['btn-lg'] },
+        size == 'small' ? { class: ['btn-sm'] },
+        disabled ? { disabled: true, class: ['btn-disabled'] },
+        loading ? { 'aria-busy': 'true', class: ['btn-loading'] },
+    ) %}
+
+    {# Example with variant='primary', size='large', disabled=false, loading=true:
+
+       The false values (secondary variant, small size, disabled state) are ignored.
+
+       button_attrs is:
+       {
+           type: 'button',
+           class: ['btn', 'btn-primary', 'btn-lg', 'btn-loading'],
+           'aria-busy': 'true'
+       }
+    #}
+
+Merging Rules
+-------------
+
+The filter follows these rules when merging attribute values:
+
+**Scalar values**: Later values override earlier ones.
+
+.. code-block:: twig
+
+    {% set result = {id: 'old'}|html_attr_merge({id: 'new'}) %}
+    {# result: {id: 'new'} #}
+
+**Array values**: Arrays are merged like in PHP's ``array_merge`` function - numeric keys are
+appended, non-numeric keys replace.
+
+.. code-block:: twig
+
+    {# Numeric keys (appended): #}
+    {% set result = {class: ['btn']}|html_attr_merge({class: ['btn-primary']}) %}
+    {# result: {class: ['btn', 'btn-primary']} #}
+
+    {# Non-numeric keys (replaced): #}
+    {% set result = {class: {base: 'btn', size: 'small'}}|html_attr_merge({class: {variant: 'primary', size: 'large'}}) %}
+    {# result: {class: {base: 'btn', size: 'large', variant: 'primary'}} #}
+
+.. note::
+
+    Remember, attribute mappings passed to or returned from this filter are regular
+    Twig mappings after all. If you want to completely replace an attribute value
+    that is an iterable with another value, you can use the :doc:`merge <../filters/merge>`
+    filter to do that.
+
+**``MergeableInterface`` implementations**: For advanced use cases, attribute values can be objects
+that implement the ``MergeableInterface``. These objects can define their own, custom merge
+behavior that takes precedence over the default rules. See the docblocks in that interface
+for details.
+
+.. note::
+
+    The ``html_attr_merge`` filter is part of the ``HtmlExtension`` which is not
+    installed by default. Install it first:
+
+    .. code-block:: bash
+
+        $ composer require twig/html-extra
+
+    Then, on Symfony projects, install the ``twig/extra-bundle``:
+
+    .. code-block:: bash
+
+        $ composer require twig/extra-bundle
+
+    Otherwise, add the extension explicitly on the Twig environment::
+
+        use Twig\Extra\Html\HtmlExtension;
+
+        $twig = new \Twig\Environment(...);
+        $twig->addExtension(new HtmlExtension());
+
+Arguments
+---------
+
+The filter accepts a variadic list of arguments to merge. Each argument can be:
+
+* A map of attributes
+* ``false`` or ``null`` (ignored, useful for conditional merging)
+* An empty string ``''`` (ignored, to support implicit else in ternary operators)
+
+.. seealso::
+
+    :ref:`html_attr`,
+    :doc:`html_attr_type`

doc/filters/html_attr_type.rst

@@ -0,0 +1,123 @@
+``html_attr_type``
+==================
+
+.. _html_attr_type:
+
+.. versionadded:: 3.24
+
+    The ``html_attr_type`` filter was added in Twig 3.24.
+
+The ``html_attr_type`` filter converts arrays into specialized attribute value
+objects that implement custom rendering logic. It is designed for use
+with the :ref:`html_attr` function for attributes where
+the attribute value follows special formatting rules.
+
+.. code-block:: html+twig
+
+    <img {{ html_attr({
+        srcset: ['small.jpg 480w', 'large.jpg 1200w']|html_attr_type('cst')
+    }) }}>
+
+    {# Output: <img srcset="small.jpg 480w, large.jpg 1200w"> #}
+
+Available Types
+---------------
+
+Space-Separated Token List (``sst``)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Used for attributes that expect space-separated values, like ``class`` or
+``aria-labelledby``:
+
+.. code-block:: html+twig
+
+    {% set classes = ['btn', 'btn-primary']|html_attr_type('sst') %}
+
+    <button {{ html_attr({class: classes}) }}>
+        Click me
+    </button>
+
+    {# Output: <button class="btn btn-primary">Click me</button> #}
+
+This is the default type used when the :ref:`html_attr` function encounters an
+array value (except for ``style`` attributes).
+
+Comma-Separated Token List (``cst``)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Used for attributes that expect comma-separated values, like ``srcset`` or
+``sizes``:
+
+.. code-block:: html+twig
+
+    <img {{ html_attr({
+        srcset: ['image-1x.jpg 1x', 'image-2x.jpg 2x', 'image-3x.jpg 3x']|html_attr_type('cst'),
+        sizes: ['(max-width: 600px) 100vw', '50vw']|html_attr_type('cst')
+    }) }}>
+
+    {# Output: <img srcset="image-1x.jpg 1x, image-2x.jpg 2x, image-3x.jpg 3x" sizes="(max-width: 600px) 100vw, 50vw"> #}
+
+Inline Style (``style``)
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Used for style attributes. Handles both maps (property - value pairs) and sequences (CSS declarations):
+
+.. code-block:: html+twig
+
+    {# Associative array #}
+    {% set styles = {color: 'red', 'font-size': '14px'}|html_attr_type('style') %}
+
+    <div {{ html_attr({style: styles}) }}>
+        Styled content
+    </div>
+
+    {# Output: <div style="color: red; font-size: 14px;">Styled content</div> #}
+
+    {# Numeric array #}
+    {% set styles = ['color: red', 'font-size: 14px']|html_attr_type('style') %}
+
+    <div {{ html_attr({style: styles}) }}>
+        Styled content
+    </div>
+
+    {# Output: <div style="color: red; font-size: 14px;">Styled content</div> #}
+
+The ``style`` type is automatically applied by the :ref:`html_attr` function when
+it encounters an array value for the ``style`` attribute.
+
+.. note::
+
+    The ``html_attr_type`` filter is part of the ``HtmlExtension`` which is not
+    installed by default. Install it first:
+
+    .. code-block:: bash
+
+        $ composer require twig/html-extra
+
+    Then, on Symfony projects, install the ``twig/extra-bundle``:
+
+    .. code-block:: bash
+
+        $ composer require twig/extra-bundle
+
+    Otherwise, add the extension explicitly on the Twig environment::
+
+        use Twig\Extra\Html\HtmlExtension;
+
+        $twig = new \Twig\Environment(...);
+        $twig->addExtension(new HtmlExtension());
+
+Arguments
+---------
+
+* ``value``: The sequence of attributes to convert
+* ``type``: The attribute type. One of:
+
+  * ``sst`` (default): Space-separated token list
+  * ``cst``: Comma-separated token list
+  * ``style``: Inline CSS styles
+
+.. seealso::
+
+    :ref:`html_attr`,
+    :ref:`html_attr_merge`

doc/filters/index.rst

@@ -26,6 +26,8 @@ Filters
     format_datetime
     format_number
     format_time
+    html_attr_merge
+    html_attr_type
     html_to_markdown
     inline_css
     inky_to_html