✏️ Editing: template-functions.php

<?php
/**
 * Functions which enhance the theme by hooking into WordPress
 *
 * @package WordPress
 * @subpackage Twenty_Nineteen
 * @since 1.0.0
 */

/**
 * Adds custom classes to the array of body classes.
 *
 * @param array $classes Classes for the body element.
 * @return array
 */
function twentynineteen_body_classes( $classes ) {

if ( is_singular() ) {
		// Adds `singular` to singular pages.
		$classes[] = 'singular';
	} else {
		// Adds `hfeed` to non singular pages.
		$classes[] = 'hfeed';
	}

// Adds a class if image filters are enabled.
	if ( twentynineteen_image_filters_enabled() ) {
		$classes[] = 'image-filters-enabled';
	}

return $classes;
}
add_filter( 'body_class', 'twentynineteen_body_classes' );

/**
 * Adds custom class to the array of posts classes.
 */
function twentynineteen_post_classes( $classes, $class, $post_id ) {
	$classes[] = 'entry';

return $classes;
}
add_filter( 'post_class', 'twentynineteen_post_classes', 10, 3 );

/**
 * Add a pingback url auto-discovery header for single posts, pages, or attachments.
 */
function twentynineteen_pingback_header() {
	if ( is_singular() && pings_open() ) {
		echo '<link rel="pingback" href="', esc_url( get_bloginfo( 'pingback_url' ) ), '">';
	}
}
add_action( 'wp_head', 'twentynineteen_pingback_header' );

/**
 * Changes comment form default fields.
 */
function twentynineteen_comment_form_defaults( $defaults ) {
	$comment_field = $defaults['comment_field'];

// Adjust height of comment form.
	$defaults['comment_field'] = preg_replace( '/rows="\d+"/', 'rows="5"', $comment_field );

return $defaults;
}
add_filter( 'comment_form_defaults', 'twentynineteen_comment_form_defaults' );

/**
 * Filters the default archive titles.
 */
function twentynineteen_get_the_archive_title() {
	if ( is_category() ) {
		$title = __( 'Category Archives: ', 'twentynineteen' ) . '<span class="page-description">' . single_term_title( '', false ) . '</span>';
	} elseif ( is_tag() ) {
		$title = __( 'Tag Archives: ', 'twentynineteen' ) . '<span class="page-description">' . single_term_title( '', false ) . '</span>';
	} elseif ( is_author() ) {
		$title = __( 'Author Archives: ', 'twentynineteen' ) . '<span class="page-description">' . get_the_author_meta( 'display_name' ) . '</span>';
	} elseif ( is_year() ) {
		$title = __( 'Yearly Archives: ', 'twentynineteen' ) . '<span class="page-description">' . get_the_date( _x( 'Y', 'yearly archives date format', 'twentynineteen' ) ) . '</span>';
	} elseif ( is_month() ) {
		$title = __( 'Monthly Archives: ', 'twentynineteen' ) . '<span class="page-description">' . get_the_date( _x( 'F Y', 'monthly archives date format', 'twentynineteen' ) ) . '</span>';
	} elseif ( is_day() ) {
		$title = __( 'Daily Archives: ', 'twentynineteen' ) . '<span class="page-description">' . get_the_date() . '</span>';
	} elseif ( is_post_type_archive() ) {
		$title = __( 'Post Type Archives: ', 'twentynineteen' ) . '<span class="page-description">' . post_type_archive_title( '', false ) . '</span>';
	} elseif ( is_tax() ) {
		$tax = get_taxonomy( get_queried_object()->taxonomy );
		/* translators: %s: Taxonomy singular name */
		$title = sprintf( esc_html__( '%s Archives:', 'twentynineteen' ), $tax->labels->singular_name );
	} else {
		$title = __( 'Archives:', 'twentynineteen' );
	}
	return $title;
}
add_filter( 'get_the_archive_title', 'twentynineteen_get_the_archive_title' );

/**
 * Determines if post thumbnail can be displayed.
 */
function twentynineteen_can_show_post_thumbnail() {
	return apply_filters( 'twentynineteen_can_show_post_thumbnail', ! post_password_required() && ! is_attachment() && has_post_thumbnail() );
}

/**
 * Returns true if image filters are enabled on the theme options.
 */
function twentynineteen_image_filters_enabled() {
	return 0 !== get_theme_mod( 'image_filter', 1 );
}

/**
 * Add custom sizes attribute to responsive image functionality for post thumbnails.
 *
 * @origin Twenty Nineteen 1.0
 *
 * @param array $attr  Attributes for the image markup.
 * @return string Value for use in post thumbnail 'sizes' attribute.
 */
function twentynineteen_post_thumbnail_sizes_attr( $attr ) {

if ( is_admin() ) {
		return $attr;
	}

if ( ! is_singular() ) {
		$attr['sizes'] = '(max-width: 34.9rem) calc(100vw - 2rem), (max-width: 53rem) calc(8 * (100vw / 12)), (min-width: 53rem) calc(6 * (100vw / 12)), 100vw';
	}

return $attr;
}
add_filter( 'wp_get_attachment_image_attributes', 'twentynineteen_post_thumbnail_sizes_attr', 10, 1 );

/**
 * Returns the size for avatars used in the theme.
 */
function twentynineteen_get_avatar_size() {
	return 60;
}

/**
 * Returns true if comment is by author of the post.
 *
 * @see get_comment_class()
 */
function twentynineteen_is_comment_by_post_author( $comment = null ) {
	if ( is_object( $comment ) && $comment->user_id > 0 ) {
		$user = get_userdata( $comment->user_id );
		$post = get_post( $comment->comment_post_ID );
		if ( ! empty( $user ) && ! empty( $post ) ) {
			return $comment->user_id === $post->post_author;
		}
	}
	return false;
}

/**
 * Returns information about the current post's discussion, with cache support.
 */
function twentynineteen_get_discussion_data() {
	static $discussion, $post_id;

$current_post_id = get_the_ID();
	if ( $current_post_id === $post_id ) {
		return $discussion; /* If we have discussion information for post ID, return cached object */
	} else {
		$post_id = $current_post_id;
	}

$comments = get_comments(
		array(
			'post_id' => $current_post_id,
			'orderby' => 'comment_date_gmt',
			'order'   => get_option( 'comment_order', 'asc' ), /* Respect comment order from Settings » Discussion. */
			'status'  => 'approve',
			'number'  => 20, /* Only retrieve the last 20 comments, as the end goal is just 6 unique authors */
		)
	);

$authors = array();
	foreach ( $comments as $comment ) {
		$authors[] = ( (int) $comment->user_id > 0 ) ? (int) $comment->user_id : $comment->comment_author_email;
	}

$authors    = array_unique( $authors );
	$discussion = (object) array(
		'authors'   => array_slice( $authors, 0, 6 ),           /* Six unique authors commenting on the post. */
		'responses' => get_comments_number( $current_post_id ), /* Number of responses. */
	);

return $discussion;
}

/**
 * Add an extra menu to our nav for our priority+ navigation to use
 *
 * @param object $nav_menu  Nav menu.
 * @param object $args      Nav menu args.
 * @return string More link for hidden menu items.
 */
function twentynineteen_add_ellipses_to_nav( $nav_menu, $args ) {

if ( 'menu-1' === $args->theme_location ) :

$nav_menu .= '<div class="main-menu-more">';
		$nav_menu .= '<ul class="main-menu">';
		$nav_menu .= '<li class="menu-item menu-item-has-children">';
		$nav_menu .= '<button class="submenu-expand main-menu-more-toggle is-empty" tabindex="-1" aria-label="More" aria-haspopup="true" aria-expanded="false">';
		$nav_menu .= '<span class="screen-reader-text">' . esc_html__( 'More', 'twentynineteen' ) . '</span>';
		$nav_menu .= twentynineteen_get_icon_svg( 'arrow_drop_down_ellipsis' );
		$nav_menu .= '</button>';
		$nav_menu .= '<ul class="sub-menu hidden-links">';
		$nav_menu .= '<li id="menu-item--1" class="mobile-parent-nav-menu-item menu-item--1">';
		$nav_menu .= '<button class="menu-item-link-return">';
		$nav_menu .= twentynineteen_get_icon_svg( 'chevron_left' );
		$nav_menu .= esc_html__( 'Back', 'twentynineteen' );
		$nav_menu .= '</button>';
		$nav_menu .= '</li>';
		$nav_menu .= '</ul>';
		$nav_menu .= '</li>';
		$nav_menu .= '</ul>';
		$nav_menu .= '</div>';

endif;

return $nav_menu;
}
add_filter( 'wp_nav_menu', 'twentynineteen_add_ellipses_to_nav', 10, 2 );

/**
 * WCAG 2.0 Attributes for Dropdown Menus
 *
 * Adjustments to menu attributes tot support WCAG 2.0 recommendations
 * for flyout and dropdown menus.
 *
 * @ref https://www.w3.org/WAI/tutorials/menus/flyout/
 */
function twentynineteen_nav_menu_link_attributes( $atts, $item, $args, $depth ) {

// Add [aria-haspopup] and [aria-expanded] to menu items that have children
	$item_has_children = in_array( 'menu-item-has-children', $item->classes );
	if ( $item_has_children ) {
		$atts['aria-haspopup'] = 'true';
		$atts['aria-expanded'] = 'false';
	}

return $atts;
}
add_filter( 'nav_menu_link_attributes', 'twentynineteen_nav_menu_link_attributes', 10, 4 );

/**
 * Add a dropdown icon to top-level menu items.
 *
 * @param string $output Nav menu item start element.
 * @param object $item   Nav menu item.
 * @param int    $depth  Depth.
 * @param object $args   Nav menu args.
 * @return string Nav menu item start element.
 * Add a dropdown icon to top-level menu items
 */
function twentynineteen_add_dropdown_icons( $output, $item, $depth, $args ) {

// Only add class to 'top level' items on the 'primary' menu.
	if ( ! isset( $args->theme_location ) || 'menu-1' !== $args->theme_location ) {
		return $output;
	}

if ( in_array( 'mobile-parent-nav-menu-item', $item->classes, true ) && isset( $item->original_id ) ) {
		// Inject the keyboard_arrow_left SVG inside the parent nav menu item, and let the item link to the parent item.
		// @todo Only do this for nested submenus? If on a first-level submenu, then really the link could be "#" since the desire is to remove the target entirely.
		$link = sprintf(
			'<button class="menu-item-link-return" tabindex="-1">%s',
			twentynineteen_get_icon_svg( 'chevron_left', 24 )
		);

// replace opening <a> with <button>
		$output = preg_replace(
			'/<a\s.*?>/',
			$link,
			$output,
			1 // Limit.
		);

// replace closing </a> with </button>
		$output = preg_replace(
			'#</a>#i',
			'</button>',
			$output,
			1 // Limit.
		);

} elseif ( in_array( 'menu-item-has-children', $item->classes, true ) ) {

// Add SVG icon to parent items.
		$icon = twentynineteen_get_icon_svg( 'keyboard_arrow_down', 24 );

$output .= sprintf(
			'<button class="submenu-expand" tabindex="-1">%s</button>',
			$icon
		);
	}

return $output;
}
add_filter( 'walker_nav_menu_start_el', 'twentynineteen_add_dropdown_icons', 10, 4 );

/**
 * Create a nav menu item to be displayed on mobile to navigate from submenu back to the parent.
 *
 * This duplicates each parent nav menu item and makes it the first child of itself.
 *
 * @param array  $sorted_menu_items Sorted nav menu items.
 * @param object $args              Nav menu args.
 * @return array Amended nav menu items.
 */
function twentynineteen_add_mobile_parent_nav_menu_items( $sorted_menu_items, $args ) {
	static $pseudo_id = 0;
	if ( ! isset( $args->theme_location ) || 'menu-1' !== $args->theme_location ) {
		return $sorted_menu_items;
	}

$amended_menu_items = array();
	foreach ( $sorted_menu_items as $nav_menu_item ) {
		$amended_menu_items[] = $nav_menu_item;
		if ( in_array( 'menu-item-has-children', $nav_menu_item->classes, true ) ) {
			$parent_menu_item                   = clone $nav_menu_item;
			$parent_menu_item->original_id      = $nav_menu_item->ID;
			$parent_menu_item->ID               = --$pseudo_id;
			$parent_menu_item->db_id            = $parent_menu_item->ID;
			$parent_menu_item->object_id        = $parent_menu_item->ID;
			$parent_menu_item->classes          = array( 'mobile-parent-nav-menu-item' );
			$parent_menu_item->menu_item_parent = $nav_menu_item->ID;

$amended_menu_items[] = $parent_menu_item;
		}
	}

return $amended_menu_items;
}
add_filter( 'wp_nav_menu_objects', 'twentynineteen_add_mobile_parent_nav_menu_items', 10, 2 );

/**
 * Convert HSL to HEX colors
 */
function twentynineteen_hsl_hex( $h, $s, $l, $to_hex = true ) {

$h /= 360;
	$s /= 100;
	$l /= 100;

$r = $l;
	$g = $l;
	$b = $l;
	$v = ( $l <= 0.5 ) ? ( $l * ( 1.0 + $s ) ) : ( $l + $s - $l * $s );
	if ( $v > 0 ) {
		$m;
		$sv;
		$sextant;
		$fract;
		$vsf;
		$mid1;
		$mid2;

$m       = $l + $l - $v;
		$sv      = ( $v - $m ) / $v;
		$h      *= 6.0;
		$sextant = floor( $h );
		$fract   = $h - $sextant;
		$vsf     = $v * $sv * $fract;
		$mid1    = $m + $vsf;
		$mid2    = $v - $vsf;

switch ( $sextant ) {
			case 0:
				$r = $v;
				$g = $mid1;
				$b = $m;
				break;
			case 1:
				$r = $mid2;
				$g = $v;
				$b = $m;
				break;
			case 2:
				$r = $m;
				$g = $v;
				$b = $mid1;
				break;
			case 3:
				$r = $m;
				$g = $mid2;
				$b = $v;
				break;
			case 4:
				$r = $mid1;
				$g = $m;
				$b = $v;
				break;
			case 5:
				$r = $v;
				$g = $m;
				$b = $mid2;
				break;
		}
	}
	$r = round( $r * 255, 0 );
	$g = round( $g * 255, 0 );
	$b = round( $b * 255, 0 );

if ( $to_hex ) {

$r = ( $r < 15 ) ? '0' . dechex( $r ) : dechex( $r );
		$g = ( $g < 15 ) ? '0' . dechex( $g ) : dechex( $g );
		$b = ( $b < 15 ) ? '0' . dechex( $b ) : dechex( $b );

return "#$r$g$b";

}

return "rgb($r, $g, $b)";
}

✏️ Editing: template-functions.php

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