Scalafix Linting Rule to find default value substitution
Java Wrapper class objects can be used interchangeably with Scala Values. The compiler is smart to automatically unbox them.
However since Java Wrapper classes exists as objects, they can be null. In this case the compiler doesn't cry, at runtime,
it takes default value of the Java Primitive type and substitutes that.
Consider a function object.getSomeLongField returns java.lang.Long
And this is passed to another function which takes a scala value,
def innocentCode(value: Long): Unit as innocentCode(object.getSomeLongField)
then it compiles, and at runtime, the innocentCode gets a 0 when object.getSomeLongField returns null
This happens because of the following problem, where a null gets converted to a 0 without any error at runtime.
scala> null.asInstanceOf[java.lang.Long].toLong
res0: Long = 0This is a linting tool, which points out these converstions in code.
Add the following plugin to plugins.sbt
addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.0")Start sbt shell.
$ sbtEnable Scalafix and run the rule as follows:
sbt> scalafixEnable
sbt> scalafix --rules=github:anish749/scala-lint-default-substitution/CheckJavaDefaultValueSubstitution