Allow relative base URI in merge.

[ioquatix]

I have needed this feature on several occasions, for example, when handling intermediate URI path computations.

[ioquatix]

I checked, and Python appears to support this without any extra flag:

#!/usr/bin/env python3
from urllib.parse import urljoin

bases = [
    'a/b/c',         # relative base (no trailing slash)
    'a/b/c/',        # relative base (trailing slash)
    '/a/b/c',        # absolute path base
    'http://ex/a/b/c' # absolute URL base
]
rels = ['d/e', '../x', '/z', '']

for b in bases:
    print(f"\nBase: {b!r}")
    for r in rels:
        print(f"  urljoin({b!r}, {r!r}) -> {urljoin(b, r)!r}")

This would be the ideal case for me (no extra flag).

If we can be compatible with Python, we just need to delete:

      unless self.absolute?
        raise BadURIError, "both URI are relative"
      end

[HoneyryderChuck]

thx for the patch @ioquatix 🙏 I report this recently here, and was going to patch it myself until I saw your PR.

IMO I think that uri should do the same as python, i.e. if the merge is relative (the origin is the same), then the user info should be retained. Bear in mind I say "origin", as in, if the hostname is the same but any of the scheme or port does, then the library can assume that the merge is unsafe and the userinfo shall be reset.

[ioquatix]

@HoneyryderChuck do you want to work on this PR? Happy to pass it over to you.

[HoneyryderChuck]

I think I was too tired when I saw your PR, I don't think it has anything to do with the issue I opened, which is about wiping out the userinfo when certain parameters update. sorry about that.