error: expected expression, found `let` statement
  --> $DIR/issue-92893.rs:1:22
   |
LL | struct Bug<A = [(); (let a = (), 1).1]> {
   |                      ^^^

error: `let` expressions are not supported here
  --> $DIR/issue-92893.rs:1:22
   |
LL | struct Bug<A = [(); (let a = (), 1).1]> {
   |                      ^^^^^^^^^^
   |
   = note: only supported directly in conditions of `if` and `while` expressions

error: aborting due to 2 previous errors