Loss of Precision error not correct

[non]

It's not enough to use a string constant with BigDecimal and a large decimal expansion, you have to actually provide your own MathContext:

scala> BigDecimal("0.12958129581958395829583295823958329852395832958295382")
res0: scala.math.BigDecimal = 0.1295812958195839582958329582395833

scala> BigDecimal("0.12958129581958395829583295823958329852395832958295382", new java.math.MathContext(200))
res1: scala.math.BigDecimal = 0.12958129581958395829583295823958329852395832958295382

I'm not sure the best way to word the warning, but I think the current warning is misleading.

[HairyFotr]

Interesting, I'll change the warning, and also try to detect the loss of precision for String. Thanks!

[non]

That's a good idea. For numbers that don't use scientific notation you can just remove the dot, and count the digits.

scala> BigDecimal("1.234567", new java.math.MathContext(7))
res7: scala.math.BigDecimal = 1.234567

scala> BigDecimal("1.234567", new java.math.MathContext(6))
res8: scala.math.BigDecimal = 1.23457

The default MathContext used by BigDecimal has 34 digits of precision. I don't know that the language guarantees this, but I also don't imagine it changing soon, so it's probably safe to hardcode that for now.

[non]

(That said, if you're using a compiler plugin or macro, you can actually create your own BigDecimal and see how much precision its MathContext has, which should be relatively future-proof.)

[HairyFotr]

I did a very hacky checker for strings, but I think it works for most cases... Will revisit in a few days to fix a few issues and to clean it up, and then I'm closing.