SE-0279: Multiple Trailing Closures

[anandabits (Matthew Johnson)]

@xwu

Wait, you’d want to deprecate existing syntax, breaking source for those who use warnings as errors?! I certainly disagree that this would be reasonable. The bar for breaking source is active harm.

I don't think new warnings is considered breaking source. Warnings as errors is a choice users make which may occasionally require source changes that would not otherwise be necessary.