core - Question about the template-loader.php file

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I am studying the WP code and have a doubt regarding the end of the /wp-includes/template-loader.php file, which handles the template that must be loaded for a certain URL request.

if($template = apply_filters('template_include', $template)){
    include($template);
}elseif(current_user_can('switch_themes')){
    $theme = wp_get_theme();
    if($theme->errors()){
        wp_die($theme->errors());
    }
}

The first part is very clear. A certain template has been set to be loaded and WP offers the possibility to filter it before proceeding.

But I don't get the second part of it.

From the wp_get_theme() documentation, $theme will contain a Theme object. But then nothing is being included, so nothing is actually happening.

What is the purpose of that?

I am studying the WP code and have a doubt regarding the end of the /wp-includes/template-loader.php file, which handles the template that must be loaded for a certain URL request.

if($template = apply_filters('template_include', $template)){
    include($template);
}elseif(current_user_can('switch_themes')){
    $theme = wp_get_theme();
    if($theme->errors()){
        wp_die($theme->errors());
    }
}

The first part is very clear. A certain template has been set to be loaded and WP offers the possibility to filter it before proceeding.

But I don't get the second part of it.

From the wp_get_theme() documentation, $theme will contain a Theme object. But then nothing is being included, so nothing is actually happening.

What is the purpose of that?

• php
• core

Share Improve this question edited Feb 22, 2021 at 14:56 Álvaro Franz asked Feb 22, 2021 at 14:39 Álvaro FranzÁlvaro Franz 1,10011 gold badge99 silver badges3131 bronze badges 2

• What is your question? The second part is also clear: If $template is falsey, then check if the user has permissions to switcht themes. If the theme object contains any errors, show them and stop execution afterwards. – kero Commented Feb 22, 2021 at 14:53
• @kero But what if the theme does not contain any error? Is that not somehow random? "Let's check if the theme has any error, but do nothing with it". Why? Of course if it's there it is very probably serving a purpose, but I did not find out what it is. – Álvaro Franz Commented Feb 22, 2021 at 15:02

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1 Answer 1

Sorted by: Reset to default 4

The conditional first checks against what gets returned from the template_include hook. In most cases, a template will be found, and there will be no issue. We'll only move onto the 2nd conditional if template_include cannot find or cannot load the template. We then look at the WP_Theme object, which does some base-line checks to see if something is wrong with the theme. You can look at the linked WP_Theme object to see which errors can be generated, but it's generally just making sure that the theme is reachable and readable. If something is critically wrong with the theme, it adds a notice to the object and displays it to the user to fix the error.

Do note that this error would only show up to a logged-in user with the switch themes capability (administrators by default). Presumably, they would know how to fix the error or escalate the issue to someone who does.

If there's nothing wrong with the theme, it's assumed to either be intentionally left out or user error ( i.e., bad filename or misspelling ). It would be unreasonable to check a file-directory for similarly named templates. It would be unreasonable to error out on a missing template if it were intentionally left out.

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