`BigInt(1) to BigInt(3)` gives infix warning under `-source:3.1`

[SethTisue]

as expected 1 to 3 doesn't warn, but BigInt does. 3.0.0-M1 with -source:3.1:

scala> 1 to 5                                                                                                           
val res0: scala.collection.immutable.Range.Inclusive = Range 1 to 5

scala> BigInt(1) to BigInt(5)                                                                                           
1 |BigInt(1) to BigInt(5)
  |          ^^
  |Alphanumeric method to is not declared @infix; it should not be used as infix operator.
  |The operation can be rewritten automatically to `to` under -deprecation -rewrite.
  |Or rewrite to method syntax .to(...) manually.
val res1: scala.collection.immutable.NumericRange.Inclusive[BigInt] = NumericRange 1 to 5

I looked at checkValidInfix in Checking.scala, but it wasn't apparent to me what the problem is.

on Gitter, @smarter agreed this is weird/wrong:

ah, checkValidInfix checks !meth.maybeOwner.is(Scala2x)
so it shouldn't be warning on the BigInt

[som-snytt]

Workaround is... multi-arg infix! Which isn't deprecated yet!

Two wrongs make a right! You can't have too much of a bad thing! etc.

@main def test() = println {
  //BigInt(1) to BigInt(10)
  BigInt(1) to (BigInt(10), BigInt(1))
}

The ownership test fails, perhaps, because of the rewrite for the default arg. (to is overloaded for Int.)

[deanwampler]

Also affects BigDecimal. I didn't try others...

[SethTisue]

because of the rewrite for the default arg

yes, exactly, as @dwijnand and I found at #13714 (which is now ready for review)