How to prevent newline from appearing in shortcode?

Question

I have created an extremely simple shortcode:

function my_shortcode($atts, $content) {
    return '<div class="block">' . do_shortcode($content) . '</div>';
}

add_shortcode('block', 'my_shortcode');

Then, in the Text (HTML) editor for a page, I enter:

[block]<h2>Test</h2>[/block]

I expect the shortcode to render as:

<div class="block"><h2>Test</h2></div>

But instead I get:

<div class="block"><br /><h2>Test</h2></div>

Why is WordPress inserting a <br />? Is there a way to prevent this behavior or at least work around it?

Answer 1

The <br> tag is coming from wpautop(), which is one of a number of display filters added to the content via wp-includes/default-filters.php:

// Display filters
add_filter( 'the_content', 'wptexturize'                       );
add_filter( 'the_content', 'convert_smilies',               20 );
add_filter( 'the_content', 'wpautop'                           );
add_filter( 'the_content', 'shortcode_unautop'                 );
add_filter( 'the_content', 'prepend_attachment'                );
add_filter( 'the_content', 'wp_make_content_images_responsive' );

...

// Shortcodes
add_filter( 'the_content', 'do_shortcode', 11 ); // AFTER wpautop()

WordPress runs the do_shortcode filter after wpautop has has already been run on the content.

Here's a function that will remove the <br> tag (source):

function shortcode_wpautop_fix( $content ) {

    // Define your shortcodes to filter, '' filters all shortcodes
    $shortcodes = array( '' );

    foreach ( $shortcodes as $shortcode ) {

        $array = array (
            '<p>[' . $shortcode => '[' .$shortcode,
            '<p>[/' . $shortcode => '[/' .$shortcode,
            $shortcode . ']</p>' => $shortcode . ']',
            $shortcode . ']<br />' => $shortcode . ']'
        );

        $content = strtr( $content, $array );
    }

    return $content;
}
add_filter( 'the_content', 'shortcode_wpautop_fix' );

An alternative approach is to ensure that do_shortcode is applied before wpautop. This can be accomplished by changing the priority of the display filters.

remove_filter( 'the_content', 'wpautop' );
add_filter( 'the_content', 'wpautop', 99 );
add_filter( 'the_content', 'shortcode_unautop', 100 );

Note that do_shortcode is already run at priority 11, so the goal of running it before wpautop is accomplished with the code immediately above.

Also worth noting, shortcode_unautop deals specifically with the markup on the outside of the shortcode, not the inside.