Enable the implementation of subcommands about taskcluster-cli

[yannlandry]

As of now, I'm on it. I'll need to figure out more than a few things but once we're there we should be able to register commands in the form of a tree.

[yannlandry]

Okay, I've spent a good deal of time thinking and reading up on other issues and it seems the best solution would be to design a custom parser for our needs.

Here is the idea I came up with. Assume the following command/subcommand structure:

   taskcluster
   |         |
help     +---slugid------+
        /    |    |       \
      v4  encode  decode  nice

The new parser would make it easy to create a CommandProvider for each command and each of its subcommands.

To register taskcluster slugid, I would do extpoints.Get("taskcluster").Get("slugid").Register(slugid{}). To register subcommand encode under slugid, I would do extpoints.Get("taskcluster").Get("slugid").Get("encode").Register(encode{}).

It would be possible to register a CommandProvider at each node/leaf of the tree (including the root taskcluster itself), and also to add code to be executed everytime a command under slugid is called.

Obviously, there would also be options to add flags and options to each command and sub*command.

This would resolve:

• The present issue
• Issue #68, and give us metadata about options and subcommands
• Issue #64 (somewhat), and help tab completion

[yannlandry]

Currently trying out github.com/alecthomas/kingpin as @t0xicCode suggested to see if it would work for us.

[yannlandry]

Going custom. Built a command-definition system yesterday, and soon we'll have a parser/framework to go with that. See it in branch subcommands.

[yannlandry]

Today's update:

Added/fixed/changed a few things, and moved the code to a new package named commander. This way we might be able to export this under a new project at some point.

I'll try to do the parser in the next few days and have something working for our meeting on Friday.

[t0xicCode]

https://github.com/spf13/cobra?

[yannlandry]

Didn't see this one while looking for possible packages to use... some features look similar, interestingly. I didn't look into it too much, however at this point I've got pretty much everything down, including the parser.

[t0xicCode]

While I don't want you to lose all the work you did, would it make sense to still try the library? If we can use an external library that we don't have to maintain and support, that'd leave more time for use to work on the specific features of the tool.

And cobra has bash completion "for free" as well 😄

[djmitche]

My notes from the meeting on Friday indicate we decided:

• spend a week working to use Cobra
• we may be able to move to the new system subcommand-by-subcommand. @yannlandry will work on a transition plan

[yannlandry]

Pull request for step 1 online.

See the transition plan for more details.

[t0xicCode]

Closed by #99.