Invalid Recursive Enum (2+ occurances) causes compiler out-of-memory on beta/nightly

[alex-ozdemir]

For example, compiling

enum Expr {
    Plus(Expr, Expr),
    Literal(i64),
}

with rustc causes the error message fatal runtime error: out of memory

Single occurrences seem to work fine.

[nikomatsakis]

Yeah, I can imagine why this is happening. We are exploring out the nested obligations in a breadth-first-fashion, and hence this blows up memory usage dramatically.

[nikomatsakis]

triage: P-high