feat: promisify clean

[imatlopez]

Checklist

• npm install && npm test passes
• tests are included
• commit message follows commit guidelines

Description of change

Promisifying the clean action such that it is similar to #2220 and #2225

[DeeDeeG]

Hi, this PR looks good to me other than a small thing!

There is a gray line undefined output to the console with this PR.

Example output:

Before:

% /Users/[me]/node-gyp/bin/node-gyp.js clean
gyp info it worked if it ends with ok
gyp info using node-gyp@7.1.2
gyp info using node@10.24.1 | darwin | x64
gyp info ok 

After:

% /Users/[me]/node-gyp/bin/node-gyp.js clean
gyp info it worked if it ends with ok
gyp info using node-gyp@7.1.2
gyp info using node@10.24.1 | darwin | x64
undefined
gyp info ok 

I think this line I am commenting on is implicitly returning a variable that exists but has value undefined to the callback. Whereas before the callback was simply called with no argument.

It's the difference between console.log() and var a; console.log(a). One logs nothing, the other logs undefined.

My suggestion is to add parentheses to indicate calling the callback with no argument whatsoever if the Promise succeeded/was fulfilled. See code suggestion here:

Suggested change

	clean(gyp, argv).then(callback.bind(undefined, null), callback)
	clean(gyp, argv).then(callback.bind(undefined, null)(), callback)

(Of course I am not a maintainer here, but I wanted to review this since you were kind enough to review my PR.)

[DeeDeeG]

P.S. I admit I don't understand the need to bind the callback, and the output seems the same to me (i.e. there is no output) with or without using .bind().

(I am a somewhat beginner or intermediate level JS programmer, so I don't really understand bind that fully in any scenario. I only mean that the code appears to log the same output and be apparently functionally equivalent in my testing with or without using .bind() on the callback.)

If it's possible to omit the .bind() in the Promise succeeded/fulfilled case, then I would personally think that's better for making the code simpler and more readable.

[imatlopez]

thanks, made the onFulfilled function simply call callback no args. Goal of mine is to replace the callbacks with promises altogether as the backbone.

the bind is because we want to return any fulfilled return as a second arg never as the first. The issue is that promises always return something (even if it is undefined) which while it would still work without bind it would break at some point.

[DeeDeeG]

Thanks for the explanation!

[DeeDeeG]

FWIW (though I'm not a maintainer here) I approve because:

• It's functionally equivalent
• It uses Promises and modern const instead of callbacks and var