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is_type_structurally_recursive diverges on some structurally recursive types #74224
Description
For example, compilation of the following program diverges:
struct A<T> {
x: T,
y: A<A<T>>,
}
struct B {
z: A<usize>
}
fn main() {}Found while examining issue from #74201, but this one has a different root cause.
rustc log
[DEBUG rustc_middle::ty::util] is_type_representable: A<T>
[DEBUG rustc_middle::ty::util] is_type_structurally_recursive: A<T> x.rs:1:1: 4:2 (#0)
[DEBUG rustc_middle::ty::util] is_type_structurally_recursive: T x.rs:2:8: 2:9 (#0)
[DEBUG rustc_middle::ty::util] is_type_structurally_recursive: A<A<T>> x.rs:3:8: 3:15 (#0)
[DEBUG rustc_middle::ty::util] SelfRecursive: A<T> contains A<A<T>>
[DEBUG rustc_middle::ty::util] is_type_representable: A<T> is SelfRecursive([x.rs:3:8: 3:15 (#0)])
error[E0072]: recursive type `A` has infinite size
--> x.rs:1:1
|
1 | struct A<T> {
| ^^^^^^^^^^^ recursive type has infinite size
2 | x: T,
3 | y: A<A<T>>,
| ------- recursive without indirection
|
help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `A` representable
|
3 | y: Box<A<A<T>>>,
| ^^^^ ^
[DEBUG rustc_middle::ty::util] is_type_representable: B
[DEBUG rustc_middle::ty::util] is_type_structurally_recursive: B x.rs:6:1: 8:2 (#0)
[DEBUG rustc_middle::ty::util] is_type_structurally_recursive: A<usize> x.rs:7:8: 7:16 (#0)
[DEBUG rustc_middle::ty::util] is_type_structurally_recursive: usize x.rs:2:8: 2:9 (#0)
[DEBUG rustc_middle::ty::util] is_type_structurally_recursive: A<A<usize>> x.rs:3:8: 3:15 (#0)
[DEBUG rustc_middle::ty::util] is_type_structurally_recursive: A<usize> x.rs:2:8: 2:9 (#0)
[DEBUG rustc_middle::ty::util] ContainsRecursive: A<usize> contains A<usize>
[DEBUG rustc_middle::ty::util] is_type_structurally_recursive: A<A<A<usize>>> x.rs:3:8: 3:15 (#0)
...
Activity
spastorino commentedon Jul 15, 2020
Assigning
P-mediumas discussed as part of the Prioritization Working Group procedure and removingI-prioritize.Rollup merge of rust-lang#85012 - FabianWolff:struct-rec, r=davidtwco
Auto merge of rust-lang#85012 - FabianWolff:struct-rec, r=davidtwco