Undefined index: echo in core files

[kellybleck]

Updated to WordPress 5.5.1, and have my WP_DEBUG set to output to an error file. There is one that crops up all the time -

[22-Sep-2020 03:39:44 UTC] PHP Notice: Undefined index: echo in /var/www/httpdocs/wp-includes/general-template.php on line 350

[davidbaumwald]

Welcome to Trac, @kellybleck! This does indeed look like something that should be investigated.

In 5.2, the $args parameter was added and made filterable with the search_form_args filter. It looks like the filtered $args could unset the echo property and throw this notice when if ( $args['echo'] ) { is run.

My guess is that a simple isset sanity check would work here.

[davidbaumwald]

Actually, this goes back to 5.2.

[SergeyBiryukov]

I think a better fix here would be to ensure that all the default values are always set:

$args = wp_parse_args( $args, apply_filters( 'search_form_args', $defaults ) );

That way we don't have to check whether each individual argument exists.

The same approach is used in comment_form(), wp_login_form(), and register_sidebar().

[SergeyBiryukov]

On second thought, that does not fix the issue and changes the behavior of the filter to no longer receive custom values. Taking another look.

[SergeyBiryukov]

In 49355:

General: Ensure that filtered arguments in get_search_form() contain all required default values.

Props kellybleck, davidbaumwald, whyisjake, SergeyBiryukov.
Fixes #51645.

[SergeyBiryukov]

Reopening for backporting to the 5.5 branch.

[SergeyBiryukov]

In 49356:

General: Ensure that filtered arguments in get_search_form() contain all required default values.

Props kellybleck, davidbaumwald, whyisjake, SergeyBiryukov.
Merges [49355] to the 5.5 branch.
Fixes #51645.