Update error msg for Parsers.scala:1738 and 1739

[ljdelight]

These error messages are for aux ctors needing non-implicit params. I'm testing the error messages with this code

class Square(val len: Int) {
  // typical cases:
  //  (1) this() parens are forgotten, (2) argument set as implicit
  def this(implicit width: Double) = this(0)
  def this = { this(4) }
}

class MyList(val s: String) {
  def this

[sebastianharko]

@ljdelight Awesome 👍 - quick tip: you can make the 'error printer' (of dotc or dotr) syntax highlight the example code (the Person class): see previous PRs related to errors :-)

[ljdelight]

Neat! I had tried to get syntax highlighting using those inline val explanation = "foobar code is "${def func()}", but it would only work with single-line insertions. I didn't realize the use of other variables and inserting those had a change on behavior, but it works great using similar to

val code = "class Person ..."
val explanation = "text ... ${code}"

I'm not sure how it works, and thanks for the tip

[felixmulder]

Perhaps the reason as to why somebody would create an auxiliary constructor with an implicit parameter is because they get the error: could not find implicit value for parameter X: Type.

It might be worth mentioning that with auxiliary constructors calling a primary constructor that has an implicit argslist, the implicit value has to be explicitly specified at the callsite.

[ljdelight]

Great feedback, I'll get this done today :D

[ljdelight]

I'm a bit over my head (learning scala from coursera, on week 7) with creating an example for the other case. I've been looking at math.Ordering and I cannot create a simple example; and my example in this PR actually does against the general consensus of not using basic types in implicit. Do you think I should remove the example and not have one? I'm considering adding more text to the explanation to help with the case of an implicit primary constructor, thoughts @felixmulder?

[felixmulder]

For the sake of progress - perhaps omit the implicit example? This can always be improved later on :)

[ljdelight]

Updated the text 👍

[felixmulder]

Basically I think this looks good, but perhaps provide an explanation and way to use aux constructors if the user has an implicit argument list in the main constructor.

[felixmulder]

Thanks @ljdelight! 🎉