URL handling tech debt

[roberth]

Describe the problem

The way Nix handles URIs/URLs can be ad hoc or inconsistent at times.

• URI prefixes aren't canonicalized
• URI prefixes don't handle ? query parameters, unless they can be mistaken for path components
• URI strings should be pushed to the program's boundary as much as possible
• URI/URL naming is unclear
• Parsing / canonicalization doesn't change the scheme to lower case (and probably more)

Expected behavior

Handle URIs and/or URLs consistently, compliantly, and only treat the as strings at the very boundary; where it's unavoidable.

nix-env --version output

Additional context

• This work was scoped out from allowed-uris: match whole schemes without slashes #9547.

Priorities

Add 👍 to issues you find important.

[a-h]

Will the URL parsing changes address #7044 ?

[roberth]

It ought to. Indeed the OpenSSH client needs host name and port to be fed separately and not as a single string in URL "authority" format (ie the thing characterized by containing the optional :).
A URL class makes such a fix a bit easier.