error: expected one of `:`, `@`, or `|`, found `<`
  --> $DIR/pat-lt-bracket-2.rs:1:7
   |
LL | fn a(B<) {}
   |       ^ expected one of `:`, `@`, or `|`
   |
   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
help: if this is a `self` type, give it a parameter name
   |
LL | fn a(self: B<) {}
   |      +++++
help: if this is a type, explicitly ignore the parameter name
   |
LL | fn a(_: B<) {}
   |      ++

error: aborting due to 1 previous error