Attempt at extra args

[perrito666]

Proposal

So, this is an idea mostly, i have not been able to test this as running mage just gets the mg from upstream, perhaps i should not use upstream?

The idea is to support this:

//go:build mage
// +build mage

package main

import (
	"fmt"

	mg "go/github.com/magefile/mage/mg"
)

func TargetOne(extra mg.ExtraArgs) {
	fmt.Printf("%#v\n", extra)
}

where ideally extra would become a string slice []string{"-baz", "blah"} after calling mage targetone foo bar -- -baz blah

Implementation

I manged to implement this by having the ExtraArgs be handled out of band with the actual Args, they are accounted by mage and the underlying generated mage file and both handle them correctly.

Ideally users of this will use this as sampled in the various targets in the tests (which is to say, in any way they want) and they will always receive the list of arguments.

The caller should then be the one in charge of processing these, we do no processing whatsoever except removing the leading -- if the user's code implements a flag parser they can pass ExtraArgs as is and get it parsed. If they want to just give this to a sub-process they can append to the arg list adding again --.

This does not solve the issue of people wanting to pass arbitrary arguments to targets, but solves the way to at least being able to pass some form of arbitrary arguments (useful,again, for invoking sub-processes that take external modifyers by commandline)

Note: every target implementing ExtraArgs will receive the same copy of the slice, it is their responsibility to process them.

[perrito666]

Ok @natefinch this works now as I intended, let me know if this is something we want to support.

[natefinch]

I think we need a test where we run mage.ParseAndRun() and pass in a raw args list and see that it does the right thing. Right now, the code in mage/main.go in the Parse function is never tested, and that's pretty key.

[perrito666]

@natefinch done, added the same test cases, which i consider to be relevant but also using ParseAndRun