AST alt arms should take an expression instead of a block

[brson]

The parser is inserting an extra block into every alt arm.

[brson]

I started on this but hit some code in the auto_serializer that I didn't understand.

[graydon]

non-critical for 0.6, de-milestoning

[catamorphism]

Doing this between builds.

[pnkfelix]

Visiting for triage, email from 2013 sep 30.

@catamorphism did you make progress on it?

[catamorphism]

@pnkfelix Sort of -- I made some progress in a branch but then I broke everything. I'm still planning to get to it, but given that it would be hard to rebase, maybe someone should just start over.

[pnkfelix]

@catamorphism can you provide a pointer to the branch, in case someone wants to look at your commits as inspiration and/or basis for work estimate?

[catamorphism]

@pnkfelix: Sure, here it is: https://github.com/catamorphism/rust/tree/issue-3085-totally-broken

It's not rebased at all. I don't even remember the error message I was getting -- just that I felt like I was getting somewhere and then suddenly, something incomprehensible and seemingly unrelated (possibly related to deriving(Encodable) and so on?) was broken, and I gave up.

[huonw]

Triage, no change; I might have a go at this later.