error[E0403]: the name `S` is already used for a generic parameter in this item's generic parameters
  --> $DIR/issue-103790.rs:4:29
   |
LL | struct S<const S: (), const S: S = { S }>;
   |                -            ^ already used
   |                |
   |                first use of `S`

error[E0107]: missing generics for struct `S`
  --> $DIR/issue-103790.rs:4:32
   |
LL | struct S<const S: (), const S: S = { S }>;
   |                                ^ expected at least 1 generic argument
   |
note: struct defined here, with at least 1 generic parameter: `S`
  --> $DIR/issue-103790.rs:4:8
   |
LL | struct S<const S: (), const S: S = { S }>;
   |        ^ -----------
help: add missing generic argument
   |
LL | struct S<const S: (), const S: S<S> = { S }>;
   |                                 +++

error[E0391]: cycle detected when computing type of `S::S`
  --> $DIR/issue-103790.rs:4:32
   |
LL | struct S<const S: (), const S: S = { S }>;
   |                                ^
   |
   = note: ...which immediately requires computing type of `S::S` again
note: cycle used when computing type of `S`
  --> $DIR/issue-103790.rs:4:1
   |
LL | struct S<const S: (), const S: S = { S }>;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0391]: cycle detected when computing type of `S`
  --> $DIR/issue-103790.rs:4:1
   |
LL | struct S<const S: (), const S: S = { S }>;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: ...which requires computing type of `S::S`...
  --> $DIR/issue-103790.rs:4:32
   |
LL | struct S<const S: (), const S: S = { S }>;
   |                                ^
   = note: ...which again requires computing type of `S`, completing the cycle
note: cycle used when collecting item types in top-level module
  --> $DIR/issue-103790.rs:1:1
   |
LL | / #![feature(generic_const_exprs)]
LL | | #![allow(incomplete_features)]
LL | |
LL | | struct S<const S: (), const S: S = { S }>;
...  |
LL | |
LL | | fn main() {}
   | |____________^

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0107, E0391, E0403.
For more information about an error, try `rustc --explain E0107`.