Bad error message when not enough type arguments in method call

[Theodus]

Code:

use "collections"

actor Main
  new create(env: Env) =>
    let xs = List[USize]
    xs.map(lambda(n: USize): I64 => n.i64() end)

Output:

Error:
/usr/local/ponyc/packages/collections/list.pony:247:10: not enough type arguments
  fun map[B](f: {(this->A!): B^} box): List[B]^ =>
         ^
    Info:
    /usr/local/ponyc/packages/collections/list.pony:247:10: definition is here
      fun map[B](f: {(this->A!): B^} box): List[B]^ =>
             ^

The error message shows the method definition rather than the location of the error.

[Theodus]

Update: The problem is in https://github.com/ponylang/ponyc/blob/master/src/libponyc/type/reify.c#L116
where the error is reported:

ast_error(opt->check.errors, typeargs, "too many type arguments");

The failure occurs in the case that typeargs is empty.