title: How do I type parseLiteral parameter in date scalar?
body: <p>How do I type <code>ast</code>?</p>
  <pre><code>import { CustomScalar, Scalar } from '@nestjs/graphql'
  import { Kind } from 'graphql'
  export class DateScalar implements CustomScalar&lt;number, Date&gt; {
    description = 'Date custom scalar type'
  
    parseValue(value: number): Date {
      return new Date(value) // value from the client
    }
  
    serialize(value: Date): number {
      return value.getTime() // value sent to the client
    }
  
    parseLiteral(ast): Date { // &lt;-- ???
      if (ast.kind === Kind.INT) {
        return new Date(ast.value)
      }
      return null
    }
  }
  </code></pre>
  <p>I tried to use</p>
  <pre><code>interface AST {
    kind: string
    value: number
  }
  </code></pre>
  <p>but then I do get the error</p>
  <pre><code>  Property 'parseLiteral' in type 'DateScalar' is not assignable to the same property in base type 'CustomScalar&lt;number, Date&gt;'.
      Type '(ast: AST) =&gt; Date' is not assignable to type 'GraphQLScalarLiteralParser&lt;Date&gt;'.
        Types of parameters 'ast' and 'valueNode' are incompatible.
          Type 'ValueNode' is not assignable to type 'AST'.
            Property 'value' is missing in type 'VariableNode' but required in type 'AST'
  </code></pre>