Warn about jQuery.nodeName removal

[timmywil]

See jquery/jquery#3475. To be removed in 4.0.

[dmethvin]

This can't be implemented until core refactors to eliminate internal calls to jQuery.nodeName. Otherwise it will throw warnings even if there are no uses in user code.

[Krinkle]

Internal callers have been fixed in jquery/jquery@ac9e301 and released in 3.2.0.

[dmethvin]

Right but in general we have said that jQuery Migrate 3.x works with jQuery 3.x. If you used an older jQuery than 3.2 it would be throwing warnings frequently. Is that considered okay? In the past we tried to avoid that.

[dmethvin]

It also complicates our test matrix since we couldn't test Migrate 3.2 with a jQuery older than 3.2 and assert no warnings.

[Krinkle]

@dmethvin I agree 3.x/3.x compat should be kept. It's our responsibility to keep that flexibility supported to reduce user confusion and upgrade smoothness. If we do want to add the warnings before Migrate 4, it would have to involve a version check.

Personally, I the complexity of a version check is worth it. The earlier the better. It would give platforms like WordPress and MediaWiki the opportunity to warn about these methods much earlier to end-users; instead of only after jQuery 4 is released.

The more users we (indirectly) enable to comfortably migrate early, the better our position is to change things in the jQuery 4 API for the benefit of everyone.

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⇒ Continuing at #254