The wp_title() check conflicts with how _s handles title tags

On a fresh Underscores-based theme, Theme Check gives the following error:

REQUIRED: The <title> tags can only contain a call to wp_title(). Use the wp_title filter to modify the output

The function on these lines of code are what’s causing it.

function _s_render_title() {
	echo '<title>' . wp_title( '|', false, 'right' ) . "</title>\n";
}

I believe this is a similar issue as outlined here and here.

This block of code is also slated to be removed in 4.3 from _s completely in favor of add_theme_support('title-tag') after it’s introduced in 4.1.

When that happens, Theme Check will throw the following error:

REQUIRED: The theme needs to have <title> tags, ideally in the header.php file.

I know I can get around this for now by just putting the <title> tag directly in the header.php file, but seeing as more and more themes will be using add_theme_support('title-tag') and the pre-4.1 shim as used in _s, I think it’s worth considering revising this check.

https://wordpress.org/plugins/theme-check/