Reserved keywords (val, def) should be rejected as an identifier

[eed3si9n]

steps

object A:
  val val = val

tree-sitter parse examples/A.scala

problem

(compilation_unit [0, 0] - [2, 0]
  (object_definition [0, 0] - [2, 0]
    name: (identifier [0, 7] - [0, 8])
    body: (template_body [0, 8] - [2, 0]
      (val_definition [1, 2] - [1, 15]
        pattern: (identifier [1, 6] - [1, 9])
        value: (identifier [1, 12] - [1, 15])))))

expectation

val should be rejected as an identifier, and it should fail to parse.

notes

Given that Scala supports infix and postfix expression, combination of expr identifier expr would be parsed as an infix expression, and since we don't reject val, def, etc a small mistake in the grammar ends up spreading widely.

[susliko]

Looks like there's no straightforward way to disallow hard keywords as identifiers until this PR lands: tree-sitter/tree-sitter#1635