error: expected identifier, found keyword `impl`
  --> $DIR/issue-81806.rs:2:1
   |
LL | trait T { const
   |         - while parsing this item list starting here
LL | impl
   | ^^^^ expected identifier, found keyword
LL | }
   | - the item list ends here
   |
help: escape `impl` to use it as an identifier
   |
LL | r#impl
   | ++

error: aborting due to 1 previous error