[bugfix] Make auto locale loading for node not mess webpack, fixes #4031, #2979, #3872

[ovangle]

Reopening this PR now that tests are passing.

Cannot import the locale relatively, since the code exists
in a different location in the bundled ES5 module than it
does in ES6.

In order to run tests locally (where the external 'moment'
library can't be loaded), fall back to using the relative import.

[maggiepint]

Yeah, that's a good change. Thanks.

[ichernev]

@ovangle can you provide some context please? What is broken, when, why.

[ovangle]

@ichernev
Sorry if I wasn't clear, this is a fix for issue #4031 (and #2979, #3872). When building with webpack and when using the ES6 sources, the build process was not able to locate the file node_modules/moment/src/lib/locale/locales/<name>, because it (rightly) doesn't exist. When using the ES5 sources, the import resolves to node_modules/moment/src/locales/<name>, which does exist.

Because webpack has no knowledge of the runtime it ignores the try/catch around the code and errors out.

The fix is to import from moment/locales/<name> because that always exists, however this doesn't work in your test environment because a library cannot declare itself as a dependency, so the original import has to be provided as a fallback.

I've stated elsewhere that I'd like this block of code removed entirely, because it isn't an ES6 compliant import (ES6 imports must be statically available), but that would be a breaking change, so I've "fixed" it for 2.x.x and will submit a fix for 3.x.x in the next couple of days.

[ovangle]

Actually looking at my changes now, I'm not so sure it resolves the issue... I tested installing from a git dependency before I added the fallback option, but I can't remember if I tested it after adding the fallback, I just noticed the unit tests were failing and it seemed like the obvious fix.

Webpack might ignore the fact that the second require is inside a catch and still error out. I'll test it tomorrow and get back to you.

[ovangle]

I installed it on a private project it using a git dependency. The require inside the catch statement is ignored by webpack. So yeah, I think it's fixed.

[ichernev]

Merged in 49819dc