crash: "Out of stack space, sorry" with structural recursive type

[elly]

The following program is sufficient to crash rustc:

tag expr {
        app(expr);
}

fn main() { }

This yields the following stack trace:

#0  0xf7fce5a1 in check_stack (task=0x87239e4) at ./src/rt/rust_upcall.cpp:30
#1  0xf7fce5d5 in upcall_get_type_desc (task=0x87239e4, curr_crate=0x0, size=12,
align=1, n_descs=2, 
    descs=0xf62a5da4) at ./src/rt/rust_upcall.cpp:528
#2  0xf7f6a5b5 in smallintmap::find () from /home/elly/a/rust/libstd.so
#3  0x0868bab2 in
middle::ast_map::new_smallintmap_adapter::adapter::method::find ()
#4  0x08133d85 in middle::ty::tag_variants ()
#5  0x08053180 in middle::trans::type_of_tag ()
#6  0x08051ec1 in middle::trans::type_of_inner ()
#7  0x08052a57 in middle::trans::type_of_inner ()
#8  0x08050b4a in middle::trans::type_of ()
#9  0x08053ad6 in middle::trans::type_of_tag ()
...

[graydon]

It's an infinite type; we didn't catch it. try app(@expr) or so.

Bug should remain open of course, since we should catch it nicely.

[catamorphism]

I just implemented the occurs check, so I'll look at this too.

[catamorphism]

On second thought, I don't think checking this is going to be very similar to the occurs check, as it doesn't involve type variables. Also, I'm not very familiar with the code that typechecks tag declarations. So I'm going to work on other bugs for now.

[msullivan]

This should be pretty easy to do using the type_structurally_contains function that marijn wrote recently. I'll take it.

[brson]

For future searching purposes, the error displayed now is 'rust: task ran out of stack'

[brson]

For future searching purposes, tag is now enum