IPV6 uri resolving creates invalid host

[Leptopoda]

Trying to resolve two IPV6 Uri's against each other yields in an invalid result:

void main() {
  final $base = Uri.parse('http://[::1]');
  final reference = Uri.parse("http://[::1]/core/img/logo/logo.svg?v=0");
  final resolved = $base.resolveUri(reference);

  print($base);     // http://[::1]
  print(reference); // http://[::1]/core/img/logo/logo.svg?v=0
  print(resolved);  // http://::1/core/img/logo/logo.svg?v=0
  
  Uri.parse('http://::1/core/img/logo/logo.svg?v=0');  // throws a FormatException 
}

I'd expect the resolved URI to also contain the brackets as defined in https://datatracker.ietf.org/doc/html/rfc3986#section-3.2.2.

A host identified by an Internet Protocol literal address, version 6
[RFC3513] or later, is distinguished by enclosing the IP literal
within square brackets ("[" and "]").

I've reproduced the issue on Dart 3.3.0 (stable) (Tue Feb 13 10:25:19 2024 +0000) on "linux_x64" and the current dartpad.

[lrhn]

The reference is a fully qualified URI, so it shouldn't do anything during resolution, just use the existing values.
Seems it uses the "host name", not the host name source.

Generally, the host getter removes the [...] braces from IPv6 addresses, which some code isn't aware of. The resolveUri is one. I think == is another, because the reference == resolved is true, while their toString()s are different, and equality of URIs should match their toString, since that's what the hashCode is computed from.

This is a problem with the API. There is no public accessible and effective way to check whether the host is an IPv6 address. It's easy to check using private members, but resolveUri accepts any implementation of the interface Uri, so it cannot assume that the object implements _Uri or _SimpleUri.

The one option is to use the toString() method or authority accessor, and then parse the host name again, which is highly inefficient.

So, rather than doing that, it should probably recognize that an input is an IPv6 address, and rewrap it. That's easy to check, if thye text contains contains a :, it's an IPv6 address.
(So call _makeHost on it, with strictIPv6: false. Should we normalize other parts of the URI as well, if we can't assume that the argument URI was normalized?)