Replace lodash 'defaults' usage with ES6 Spread initializer

[jayaddison]

Q	A
Patch: Bug Fix?	No
Major: Breaking Change?	No
Minor: New Feature?	No
Tests Added + Pass?	No
Any Dependency Changes?	No
License	MIT

This change is a follow-up to #11790 and proposes removal of usages of lodash/defaults from the codebase, to be replaced by the ES6 spread operator.

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[jayaddison]

⚠️ Nope, this isn't ready as-is; the ordering of arguments are still a problem in at least one case, I think.

[jayaddison]

(...and perhaps even the logic around undefined property handling via lodash.defaults could make it hard/impossible to simply drop-in the spread operator as a replacement)

[kaicataldo]

Do we want to do this? The documentation for _.defaults says

Once a property is set, additional values of the same property are ignored.

So if any of the objects we’re merging in contain the same key twice, this would change the behavior.

[existentialism]

@kaicataldo check out the now collapsed/outdated discussion

[jayaddison]

I do think this is still a little risky and would agree with @kaicataldo's concern, even if technically the code should be safe from a readthrough and with tests passing.

[existentialism]

I'm fine with closing and sticking with _.defaults (though I don't see it as being that risky)

[jayaddison]

Would changes like this tend to be caught by manual testing of release candidates / betas before a full release?

If the CLI & library paths here get a decent amount of pre-release exercise I think that'd tend to de-risk the changes a lot.

[coreyfarrell]

I took another look, made a suggestion for babel-traverse. From what I can tell babel-cli changes are fine (I think existing behavior is maintained).

[nicolo-ribaudo]

Thanks!