Implement specification of subcommand

[abetomo]

#532

[shadowspawn]

Long comment. 🙂

I have not done run-time testing yet, this is some initial comments.

I would like to eventually add a routine to match .action where this configuration could go, but that is a bigger job, and I assume you don't want to wait for that, which is ok!

I like that you added the support in the existing .command options so does not affecting existing code.

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Now for the requested change suggestion: I do not like subcommand as the option name.

We already have a lot of confusion over the two modes so we need a name to make it clearer that this is not relevant to .action based commands. I have been thinking about naming and considering words like "spawn" and "exec" and "external". I checked how people describe git subcommands and found "Git subcommands are standalone executables" which I thought was fairly clear.

Perhaps: "executableFile" instead of "subcommand"?

(I am not sure about "File" here, but came to that partly because node child_process has execFile. I will ask for comments on naming in the linked issue too.)

[shadowspawn]

To have behaviour consistent, I think we should calculate isExplicitJS when the option supplied name has an explicit suffix. (An easy way would be to call basename and fall through existing lookup code, but might be more appropriate to check the option supplied name directly.)

The behaviour I see is:

file        option      spawn
foo-bar                 spawn foo-bar
foo-bar.js              spawn node foo-bar.js
foo-bar.js  foo-bar     spawn node foo-bar.js (ok)
foo-bar.js  foo-bar.js  spawn foo-bar.js (surprise! did not detect file suffix)

[shadowspawn]

I don't think we need to wait any longer for feedback on executableFile, and I am still happy with that if ok with you.

[shadowspawn]

Would you like example code for the isExplicitJS feedback?

[shadowspawn]

This is being considered for v3, but some changes suggested. I am willing to help with code if wanted (in which case I'll get it reviewed before merging).

[shadowspawn]

Started work on implementing my suggestions

[shadowspawn]

Closing in favour of #999 which builds on this pull request.

[shadowspawn]

Available now as a prerelease. See #1001