Thanks for the ticket, @sphakka.

You're right that get_template_part() doesn't return a value, but if it returned the value of locate_template() I'm not sure that this would tell you anything that you don't already know. If there's a typo in your file name then an empty string will be returned. If there's no typo but the file doesn't exist, it'll still return an empty string.

The problem is that get_template_part( 'non-existing-file' ) fails silently. Of course page rendering would break, so you'd see that something is wrong, but that's not trivial without a message clue. The rationale is that something like

if ( ! get_template_part( 'I_misspelled_this_one' )
  error_log( 'I_misspelled_this_one: template file not found' );

would help spotting the mistake. It doesn't really need to report what it found (returning bool would be fine), but since locate_template() is the last statement in the code, then just having

return locate_template($templates, true, false);

would settle the matter with minimum effort ;-)

Actually, I now realize that this is an instance of a more general problem with many (all?) get_*() functions calling locate_template() at end. So, along the principle that silent failure is bad practice (unless I'm missing some obscure reason for not having the possibility of checking programmatically what goes on), a review of all those functions would be advised. That would also make them more consistent with other get_whatever() functions that already return something.

updates get_template_part to return the value of locate_template

I agree with @sphakka - I've also run into this issue and it would be useful for get_template_part not to fail silently, so we have the option to check the return value.

I've attached a patch to pass on the return value from locate_template, as suggested.

@tferry I agree with this function passing back the result of locate_template(). The docblock needs updating to reflect the new @return value; it should probably be identical to that of locate_template().

Thanks for the spot @johnbillion, docs are super important. Updated with the @return value added to the docblock.

Rather than only update get_template_part(), it'd be better to update all of the functions that call locate_template() at the same time.

This will also need an addition to the docblock for each function, along the lines of @since x.y.z Added the return value.

Updates multiple get_*() template part functions to return the value of locate_template

Thanks for the suggestion and guidance @pento

New diff uploaded to add the return values to all get_*() functions within wp-includes/general-template.php (including relevant @since and @return docblock tags)

I've left the @since version tag as literally x.y.z as I don't know when this'll be included in core, but happy to update as and when.

In 44678:

I'm re-opening this ticket, as a problem as come up.

There are ​a lot of examples of themes printing the return value of get_template_part(). The function name implies that it returns something, so this isn't really a surprising usage.

This causes two problems:

• Unexpected content being sent to the browser.
• A path disclosure security issue.

Unless anyone has good ideas for a workaround, we're going to need to revert it.

Props @david.binda for discovering this.

There's several instances in the theme directory too: ​https://wpdirectory.net/search/01D2YXN15FBXVEYPCRH8CM7K49

In 44725:

[44678] has been reverted in trunk. Moving this to 5.2 for further exploration and also marking it close. Unless a better approach can be thought of, this will probably be too risky to introduce.

Another option might be a has_template_part() function that can be used for conditional logic.

Adds a new has_template_part() function, which determines whether a template part file exists

Thanks @johnbillion, I like your suggestion of a new function - it solves the original problem while avoiding the issues of changing the return value of the existing function, as discovered. I have attached a diff with this new function for review.

I considered creating equivalent has_*() functions for get_header(), get_sidebar(), and get_footer() respectively, but the use of the theme-compat files in the locate_template() function renders these new functions redundant - they would all return true, regardless of theme files.

Thanks for the patch @tferry

Few suggestions regarding the inline documentation in 40969.4.diff​:

• Add the missing @return part.
• Add the null type.
• Mention the default name value.
• Mention that the name is optional.

So instead of this part:

* @param string $slug The slug name for the generic template.
* @param string $name The name of the specialised template.

it could be: