wp_make_link_relative() returns domain name instead of zero length string path when no path present

[adiant]

wp_make_link_relative() simply returns the URL passed to it when the URL has no path, just a domain name. Instead, it should return a zero length string.

A URL with a path of '/' correctly returns '/'.

Incorrect: var_dump( wp_make_link_relative( '​http://www.wordpress.org' ) ) displays "string(24) "​http://www.wordpress.org"

Correct: var_dump( wp_make_link_relative( '​http://www.wordpress.org/' ) ) displays string(1) "/"

Workaround: for my purposes, parse_url( $home_url, PHP_URL_PATH ) does all that I need, but wp_make_link_relative() would still be useful when a Query or Fragment is present in the URL.

[bcworkz]

Making the slash in the match expression optional does the trick.

[nacin]

Huh, I never heard of wp_make_link_relative(). Looks like it hasn't been used anywhere in core since WordPress 2.5.

I am fine with fixing this but we will need some ​unit tests, I think.

[MikeHansenMe]

tests wp_make_link_relative

[SergeyBiryukov]

In 35497:

Formatting: wp_make_link_relative() should return an empty string if no path is present in the link.

Props bcworkz, MikeHansenMe, chriscct7, SergeyBiryukov.
Fixes #26819.