ICE with pretty printing macro expanded auto_serialized tuples

[erickt]

I've put an example and stack trace in this gist: https://gist.github.com/3426928.

[dbp]

I'm going to take a look at it. The error is in this assertion:
assert arm.body.node.stmts.is_empty();

erickt has a workaround: https://gist.github.com/3428070

But possibly it will be better to get the AST structure to actually be the same. I don't know how macros work, so I'm not sure if they are doing their own AST generation (in which case, maybe auto_serialize needs to be changed), or if something more subtle is going on.

[catamorphism]

Can't reproduce with b865b4b -- I assume it got accidentally fixed since the auto-serializer has changed a bit over the past 4 months :-)

This does sound like #3121 (which is still open), though.

[catamorphism]

Added the test case ( test/run-pass/issue-3250.rs )