Pingback does not work for schemeless URLs

[tobiaskochsonlinenet]

I noticed that a pingback will not be send if the target URL is given as a schemeless URL (like //www.example.com/path/file.ext.
This is because discover_pingback_server_uri() in comment.php is using the PHP function parse_url() which cannot handle schemeless URLs correctly.

[kraftbj]

Noting that PHP docs state that 5.4.7 corrects this. ​http://php.net/manual/en/function.parse-url.php

[johnbillion]

Test coverage ought to discover_pingback_server_uri() should pick this up via ​https://github.com/aaronjorbin/develop.wordpress which gets tested on Travis.

Also ​http://3v4l.org/ is useful for testing code across PHP versions.

[dshanske]

This should work if we change to wp_parse_url

[dshanske]

Switch to wp_parse_url which has backward compatibility

[rachelbaker]

Still needs a unit test to confirm.

Trac ticket: #31384