Version 7.8.0 has a regression in URI resolution

[stof]

Bug Report

Information	Description
Package	league/uri
Version	7.8.0
PHP version	8.4.18
OS Platform	Ubuntu

Summary

Version 7.8.0 breaks the resolution of some references, making it incompatible with RFC 3986

Standalone code, or other way to reproduce the problem

use League\Uri\Uri;

$base = Uri::new('http://a/b/c/d;p?q')

var_dump($base->resolve(Uri::new('g:h')->toString());

$base2 = Uri::new('foo://a/b/c/d;p?q');

var_dump($base2->resolve(Uri::new('foo:g')->toString());

Expected result

The first dump should produce g:h and the second dump should produce foo:g.

Those test cases are coming directly from examples defined in RFC 3986.
The first failing case is the first normal example of the RFC verbatim.
The second failing case corresponds to the last abnormal example of the RFC, adapted to use the scheme foo rather than http. This adaptation is necessary to avoid an error for http:g as league/uri has a validation enforcing the usage of a hierarchical URL for the http scheme (as well as a few others), which is not the case in the example (but the fact that http is expected to be hierarchical comes from a different RFC. RFC 3986 does not define the semantic of the http scheme and so could have use any scheme in its example).

Actual result

As 7.8.0, this returns g:/h and foo:/g. The behavior was correct in 7.7.0 and older.

[stof]

For reference, this was detected by the testsuite of scssphp.
As I have ported the dart URI resolution logic to PHP (which extends the RFC3986 behavior by adding support for relative references as base, while being compatible with RFC3986 for all non-error cases of the RFC), I have tests covering all cases (and the resolution is mostly delegated to league/uri in practice).
In case you are interested in increasing test covering in your own testsuite, the relevant cases are defined in https://github.com/scssphp/scssphp/blob/1e9ff3b286deb16f9987e789cfe4b0d0f4b9ce89/tests/Util/UriUtilTest.php#L35-L93. The first part of the list defines cases coming from the RFC3986 examples. The second part of the list defines additional cases that match the RFC3986 algorithm but are not provided in the RFC examples (they should allow achieving full coverage of the valid cases). The third part of the list (outside the linked range) defines the cases for the dart extended behavior, that are not relevant for your testsuite.

[stof]

to be exact, installing league/uri 7.7.0 with league/uri-interfaces 7.8.0 also triggers the failure, so the bug is likely in league/uri-interfaces (I cannot try the opposite combination of upgrades, due to the requirement in league/uri)

[nyamsprod]

@stof I found the issue. It's an edge case fix introduced to fix another issue related to the uri-polyfill 😢
https://github.com/thephpleague/uri-src/blob/master/interfaces/UriString.php#L376-L381
I will try to come up with a better and cleaner version or will have to revert the change.

[stof]

@nyamsprod you probably need to distinguish cases that have an authority and cases that don't.

[nyamsprod]

yep the fix should be improved but that's the distinction I need to make indeed

[nyamsprod]

@stof a fix has landed in the branch you may test it. I added your tests and fixed another regression in doing so. let me know if all is good now.

[nyamsprod]

Fix has landed on the master branch