Add opam repo show <reponame> support

[ProgramingIsTheFuture]

Related to issue #6235.

Adding a new command that will allow us to get the URL and Rank of a specific repo.

Also supports all (will display the url and rank of a repo for every switch):

$ opam repo show default --all

[dra27]

(sorry, I can't get past .. as meaning the parent directory!)

[kit-ty-kate]

Thanks for this PR, i've pushed a commit to apply some of our more common coding style, so that the new code doesn't feel too out of place.

I've tried and it works reasonably well, however i've hit some issues:

$ opam repo show --switch=does-not-exist default
switch: does-not-exist
url: https://staging.opam.ocaml.org/
rank: 2

with does-not-exist being a non-existent switch and default being an existent repository.
I don't think this should return that kind of output (i would more expect something like an error).

I also think the new command should have a way to display the details of a repository that's not currently attached to any switches (maybe with --dont-select?)

I'm also wondering how useful would opam repo show -a be, but we could add it later if needed i suppose.

[ProgramingIsTheFuture]

There are some other commands with the same behaviour (abc is not defined):

$ opam repo list --switch=abc
[NOTE] These are the repositories in use by the current switch. Use '--all'
       to see all configured repositories.

<><> Repository configuration for switch abc <><><><><><><><><><><><><><><><>
 1 default https://opam.ocaml.org

Reading more the code, I found that the actual flag to select switch is --on-switch (defined here). This will produce the expected behaviour (error in case of non-existing switch).

Because --switch=<switch> doesn't populate the `Switch <switch>:

opam/src/client/opamCommands.ml

Lines 2375 to 2383 in ce734b3

	| `Switch sw ->
	if not (OpamSwitch.Set.mem sw all) &&
	not (OpamSwitch.is_external sw)
	then
	OpamConsole.error_and_exit `Not_found
	"No switch %s found"
	(OpamSwitch.to_string sw)
	else if OpamStd.List.mem OpamSwitch.equal sw acc then acc
	else acc @ [sw]

Could you please verify?

[kit-ty-kate]

Ah my bad, i thought --switch would do it without looking at the man page because of the name of the variant. --on-switch works as expected indeed.

I think we should fix --switch separately. I'll open a ticket.

[kit-ty-kate]

some more design questions:

• do we want opam repo show does-no-exist to exit 0 with no error message?
• do we want an extra name: line, even if a bit useless at the moment, it might be useful later if opam repo show -a is added
• do we want to have colors? This might help with readability (for example opam show <pkg> has its fields coloured blue)
• what is the intended way to parse the output? Wait for switch, then parse each line in this context until a new line starting with switch: ?

[kit-ty-kate]

There is probably a better way to do this but i think it would be nice to have the different switches visually separated. opam repo show -a default is quite hard to look at, at the moment

Suggested change

	List.iter (fun (sw, repos) ->
	List.iter (fun (rank, repo) ->
	let did_print_atleast_once = ref false in
	List.iter (fun (sw, repos) ->
	List.iter (fun (rank, repo) ->
	if !did_print_atleast_once then
	OpamConsole.msg "\n"
	else
	did_print_atleast_once := true;

[ProgramingIsTheFuture]

Hey @kit-ty-kate, I made the above changes.

Wait for switch, then parse each line in this context until a new line starting with switch: ?

Yes, the output should be a name, url and rank.

It now works with -a and without repo_name (it will list all repos for the current switch) and the error message is better now.