This actually doesn't cause any dependency loops in std, which is pretty
much my benchmark for it being acceptable. This can be reverted if it
turns out to be problematic, but for now, let's err on the side of
language simplicity.
To be clear, this *does* regress some cases which previously worked: I
will have to remove some behavior tests as a result of this commit. To
be honest, the tests which look to be failing as a result of this are
things which I think are generally unadvisable; I actually reckon a bit
more friction to use default field values in non-trivial ways might be a
good thing to stop people from misusing them as much. Struct fields
should very rarely have default values; about the only common situation
where they make sense is "options" structs.
Matthew Lugg
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