Load icon files dynamically as ACF select options

acf.php

<?php
/**
 * Load icons dynamically into the `icon_picker` select field.
 *
 * @param array $field field options.
 * @return array new field choices.
 *
 * @author JC Palmes
 */
function acf_load_icon_picker_field_choices( $field ) {

	// Reset choices.
	$field['choices'] = array();

	// Grab our icons array.
	$icon_folder = get_template_directory() . '/build/images/icons';
	$icons = list_files( $icon_folder, 2 );

	// Loop through icons.
	foreach ( $icons as $key => $icon ) {
		if ( is_file( $icon ) ) {
			$icon_name = basename( $icon );
		}

		// Set values.
		$field['choices'][ sanitize_title( $key ) ] = $icon_name;
	}

	// Return the field.
	return $field;
}
add_filter( 'acf/load_field/name=icon_picker', __NAMESPACE__ . '\acf_load_icon_picker_field_choices' );