Fix #3540: Implicit class with two arguments does not fail compilation

[vitorsvieira]

This PR aims #3540 and #2464.

Where:

object Test {
  implicit class Foo(i: Int, s: String)
}

And

object Foo {
  object Bar
  implicit class Bar
}

Compilation must fail providing Implicit classes must accept exactly one primary constructor parameter error message and further explanation.

[dottybot]

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[allanrenucci]

Can you add more tests here:

implicit class Foo0
implicit class Foo1()
implicit class Foo2()(x: Int)

[nicolasstucki]

You should also add

implicit case class Bar0
implicit case class Bar1()
implicit case class Bar2()(x: Int)

[vitorsvieira]

OK. When adding these tests, the number does not match, as it expects only one failure.

Wrong number of errors encountered when compiling ../out/compileNeg/neg/i3540, 

expected: 1, actual: 7

Should I change compileNeg?

[nicolasstucki]

Probably

[allanrenucci]

You simply need to add // error next to the lines that do not compile

[vitorsvieira]

👍 Added.

[allanrenucci]

Can you also add the error messages emitted by the compiler:

implicit class Foo0 // error: <the error message here>

You can get the error messages by running in sbt:

dotc tests/neg/i3540.scala

[vitorsvieira]

Added error messages to the comments.

[allanrenucci]

Can you add a pos test under tests/pos/i3540.scala:

object Test {
  implicit class Foo(x: Int)(implicit y: Int)
  implicit class Foo(x: Int)(y: Int)(implicit z: Int) // OK but not used during implicit lookup
  implicit class Foo(x: Int)(y: Int) // OK but not used during implicit lookup
}

[allanrenucci]

I would say instead:

val explanation = {
  val example = "implicit class RichDate(date: java.util.Date)"
  hl"""Implicit classes may only take one non-implicit argument in their constructor. For example:
      |
      | $example
      |
      |While it’s possible to create an implicit class with more than one non-implicit argument,
      |such classes aren’t used during implicit lookup.
      |""" + implicitClassRestrictionsText
}

[vitorsvieira]

Perfect! Updated.

[allanrenucci]

Remove this white line

[allanrenucci]

Add new line at the end of a file

[vitorsvieira]

Added.