error: expected one of `+`, `,`, `::`, `=`, or `>`, found `From`
  --> $DIR/unclosed-generics-in-impl-def.rs:1:46
   |
LL | impl<S: Into<std::borrow::Cow<'static, str>> From<S> for Canonical {}
   |                                              ^^^^ expected one of `+`, `,`, `::`, `=`, or `>`
   |
help: you might have meant to end the type parameters here
   |
LL | impl<S: Into<std::borrow::Cow<'static, str>>> From<S> for Canonical {}
   |                                             +

error: aborting due to 1 previous error