No check for infinitely sized structs

[nikomatsakis]

The following program causes a stack overflow:

struct S {
    element: Option<S>
}

fn main() {
}

There is a check that enums do not recurse in this way, but no such check for structs. (Note, though, that there is a check that structrs are instantiable, which is slightly different)

[bblum]

Huh, so that's why std::list has pointer indirections in it.

[Aatch]

This is still an issue, nominating for production ready

[graydon]

accepted for production-ready milestone

[emberian]

So uh, this... doesn't exactly reproduce. It compiles and runs fine, no overflow or anything afaict. It should be rejected by the compiler, I think.

[bblum]

@cmr you have to reference the type, just like #5146, which I triaged today. Actually I think they are the same bug.

[huonw]

This applies to non-infinite-sized types that contain themselves unboxed like the following too:

struct Foo { x: [Foo, .. 0] } // possibly ok, size is 0.

[pnkfelix]

Accepted for 1.0, P-high.