PHP Notice in strip_fragment_from_url() when schemeless URI is passed

[dd32]

Related to [52829] is this PHP Notice that seems to be triggering on a the_content filter after that change:

GET https://wordpress.org/news/2014/04/smith/

E_NOTICE: Undefined index: scheme in wp-includes/canonical.php:854
Undefined index: scheme

The input in this case is a URL such as //wordpress.org/news/files/2014/04/widgets.mp4.

I also note that strip_fragment_from_url() doesn't use wp_parse_url() but uses parse_url() directly.

Trac ticket: https://core.trac.wordpress.org/ticket/55333

[SergeyBiryukov]

In 52833:

Canonical: Check if the URL scheme exists in strip_fragment_from_url().

This avoids an "Undefined index" PHP notice when a schemeless URI is passed.

Props dd32, SergeyBiryukov.
Fixes #55333.

Thanks for the PR! Merged in https://core.trac.wordpress.org/changeset/52833.

[SergeyBiryukov]

For reference, strip_fragment_from_url() was added in [35770] / #19918.