A Scala compiler plugin for finding orphan expressions in Scala code. An orphan expression of type T occurs when the result of an expression of type T is discarded. For example, an orphan Future occurs when a Future result is not assigned to a value, returned, or otherwise transformed. This can often indicate a bug in the code.
Currently, the implementation simply checks for statements within blocks matching the configured type(s). Note that this does not cover the cases already covered by the -Ywarn-value-discard compiler option.
The demo module in this repository shows an example of warnings emitted. The output looks something like:
[warn] /Users/greg/projects/orphan-finder/demo/src/main/scala/io/methvin/orphanfinder/Demo.scala:12:11: Orphan scala.concurrent.Future found!
[warn] Future("hello")
[warn] ^
[warn] /Users/greg/projects/orphan-finder/demo/src/main/scala/io/methvin/orphanfinder/Demo.scala:15:57: Orphan scala.concurrent.Future found!
[warn] Future(throw new RuntimeException("hello")).recover {
[warn] ^
To use this plugin, add the following to build.sbt:
inThisBuild(Seq(
autoCompilerPlugins := true,
addCompilerPlugin("io.methvin" %% "orphan-finder" % orphanFinderVersion cross CrossVersion.full),
scalacOptions ++= Seq(
// Configure the orphan types you want to warn about
"-P:orphan-finder:class:scala.concurrent.Future"
)
))where orphanFinderVersion is the version you wish to use. The latest is: 