Optional Chaining: Account for document.all

[azz]

Q	A
Fixed Issues?
Patch: Bug Fix?	👍
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	👍
Documentation PR
Any Dependency Changes?

Account for document.all with the optional-chaining operator.

Input:

foo?.bar;

Output - Before:

var _foo;

(_foo = foo) == null ? void 0 : _foo.bar;

Output - After:

var _foo;

(_foo = foo) === null || _foo === void 0 ? void 0 : _foo.bar;

This is spec-compliant as per 3.8.1 Runtime Semantics: Evaluation

4. If baseValue is undefined or null, then
   Return undefined.

As this can generate a fair amount of code, and due to the rarity of document.all in practice, I've only made the change in spec mode.

NB: This will likely have merge conflicts with the files to be deleted in #6345 @jridgewell

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/5438/

[Andarist]

If we do it here only in spec mode, the same thing (introducing loose mode) imho should be done in babel-plugin-transform-nullish-coalescing-operator

[azz]

Indeed. I can do that in a follow-up PR.

[Andarist]

Sure, I didn't mean it should go into this one :)

[jridgewell]

Please add a loose test.

[nicolo-ribaudo]

@jridgewell It is already there, it just isn't shown in this PR because its output isn't modified.

https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-optional-chaining/test/fixtures/general/memoize-loose
https://github.com/babel/babel/tree/master/packages/babel-plugin-transform-optional-chaining/test/fixtures/general/function-call-loose