Allow all opam URLs in opam-repositories section

[dra27]

While working on #647, I attempted to add a repository git+file://D:\\opam-repo#branch which is a valid opam URL but which causes an exception with setup-ocaml ("Error: Invalid URL" in "Retrieve the opam download cache"). I have a recollection that fully specified opam URLs have caused problems in the past (e.g. git+https://github.com/ocaml/opam-repository). The issue looks like it's in composeOpamDownloadCacheKeys:

setup-ocaml/src/setup-ocaml/cache.ts

Lines 96 to 100 in b0fb36a

	const repositories = OPAM_REPOSITORIES.map(([, u]) => {
	const url = new URL(u);
	const urn = path.join(url.hostname, url.pathname);
	return urn;
	}).join("_");

when trying to create a URL object.

[smorimoto]

So it seems to make more sense here not to create a URL object, but simply to pass it, right?

[dra27]

I guess so - I wasn't entirely sure what existing code was trying to do. Is it trying to remove the protocol from the cache key?

[dra27]

(this was non-urgent for me, too - it was easy to work-around, and I was setting up an unusual workflow to test something)

[psafont]

I've encountered this symptom because I'm trying to convert a legacy workflow using the ocaml's docker images to setup-ocaml for testing xapi's custom repo. I don't think I can use v1 (where local repos work fine) as I need to disable opam's sandboxing.

This also happens when using "." as a shorthand of the current working directory. Maybe the url could be fetched from opam instead, or maybe just use the name of the repository? I'm not sure what is it that it's trying to solved by using the url in the key that can't be solved by using the name

[psafont]

Now the action builds the key in an ad-hoc way which takes into account relative filepaths. I'm unsure whether this is enough to cover all types of URLs supported by opam

[smorimoto]

Fixed in #656