Undefined index: host in/wp-includes/l10n.php on line 989, suggested fix

[SeBsZ]

We're using WordPress 5.3.2 and I'm getting a lot of notices: "Notice: Undefined index: host" in l10n.php on line 989:

} elseif ( ! isset( $src_url['host'] ) || $src_url['host'] === $site_url['host'] ) {

The cause in our case, is that $site_url does not have a 'host' index. I'd like to suggest that instead of only checking whether
$src_url['host'] is set, also check whether $site_url['host'] is set.

We have a filter on site_url() which makes all URLs relative. This is what causes 'host' not to be set. Regardless of the cause though, I don't think l10n.php should generate a notice in this case.

[archon810]

#46387 seems similar.

[archon810]

@SergeyBiryukov Think you can target 5.4 for this one? It's the #1 issue that keeps pinging our Sentry by a huge margin.

[SeBsZ]

I've tested the patch, and can confirm the PHP Notice is gone. I can't vouch for the correctness of the implementation though, as I didn't look into the inner workings. Thanks for the quick response @SergeyBiryukov, looking forward to seeing this released.

[SergeyBiryukov]

This still needs tests, and I'm not quite sure the patch is correct as is.

Moving to 5.6 for a closer look.

[SergeyBiryukov]

#51172 was marked as a duplicate.

[SergeyBiryukov]

#51286 was marked as a duplicate.

[justinahinon]

The initial patch proposed by Sergey still needs a look.
@nourma proposed to work on it during yesterday's i18n bug scrub.

And I can write the unit tests when ready.

[nourma]

Replying to justinahinon:

The initial patch proposed by Sergey still needs a look.
@nourma proposed to work on it during yesterday's i18n bug scrub.

And I can write the unit tests when ready.

I am unable to duplicate the undefined index in l10n.php. When I use wp_make_link_relative to filter site_url to make URLs relative, I get undefined indexes in theme.php(lines 3479 & 3544), class-wp-customize-manager.php(line 4598), and http.php(lines 421 and 422). In each case, a function is trying to access $admin_origin['host'], which has no host index. On a side note, I was able to successfully apply the patch 49145.diff (but obviously was unable to test that it actually solved the problem, since I was unable to replicate the error in l10n.php). I applied the patch on the latest build WordPress 5.6.

Trac ticket: https://core.trac.wordpress.org/ticket/49145

• Applies 49145.diff patch by @SergeyBiryukov
• Refactors tests to use data provider
• Adds test cases for no "host".

[SergeyBiryukov]

In 49639:

I18N: Avoid PHP notices for relative URLs in load_script_textdomain().

Props hellofromTonya, SeBsZ, archon810, nourma, justinahinon, SergeyBiryukov.
Fixes #49145.

Merged in changeset https://core.trac.wordpress.org/changeset/49639