Scalaxy/Parano

Extra compile-time checks that prevent some stupid mistakes (previously incubated at Scalaxy).

Can be used as a compiler plugin (preferred method), as a standalone compiler (scalaxy.parano.ParanoCompiler) or by calling a macro (scalaxy.parano.verify()).

Checks:

• Confusing names in case class extractors
• Ambiguous unnamed arguments with same type (e.g. Int parameters that could be inadvertently swapped)
• Confusing names in method calls
• (TODO) Potential side-effect free statements (e.g. missing + between multiline concatenations)

case class Foo(theFirst: Int, second: Int)

val foo = Foo(10, 12)                // Error: unnamed params theFirst and second have same type
                                     //        and are ambiguous.
val foo2 = Foo(10, second = 12)      // Fine.
val foo3 = Foo(theFirst = 10, 12)    // Fine.

val Foo(someFirst, someSecond) = foo // Fine.

val Foo(theSecond, first) = foo      // Error: theSecond used to extract Foo.theFirst,
                                     //        first used to extract Foo.second

val foo5 = Foo(theSecond, first)     // Error: ident theSecond used for param theFirst,
                                     //        ident first used for param second

Usage

If you're using sbt 0.13.0+, just put the following lines in build.sbt:

scalaVersion := "2.11.6"

autoCompilerPlugins := true

// Scalaxy/Parano plugin
addCompilerPlugin("com.nativelibs4java" %% "scalaxy-parano" % "0.4-SNAPSHOT")

// Ensure Scalaxy/Parano's plugin is used.
scalacOptions += "-Xplugin-require:scalaxy-parano"

// Scalaxy/Parano snapshots are published on the Sonatype repository.
resolvers += Resolver.sonatypeRepo("snapshots")

TODO

Ideas

• Warn against non-lazy vals in traits

• Add complete tests

• Make an exception for natural progressions: x, y, z, a, b, c, d, i1, i2, i3... (they still need mismatching names check, but no ambiguity check)

• Tuple return types in extractors: require an apply companion method with symmetric signature, take names from it and propagate accross matches:

  object MyExtractor {
    def apply(a: Int, b: Int) = ???
    def unapply(v: Any): Option[(Int, Int)] = v match {
      case ... =>
        val a = ...
        val b = ...
        (b, a) // Error: potential naming confusion (names of tuple are (a, b)).
    }
  }

Hacking

If you want to build / test / hack on this project:

• Make sure to use paulp's sbt script with sbt 0.12.2+

• Use the following commands to checkout the sources and build the tests continuously:

  git clone git://github.com/ochafik/Scalaxy.git
  cd Scalaxy
  sbt "project scalaxy-parano" "; clean ; ~test"
  

• Test with:

  git clone git://github.com/ochafik/Scalaxy.git
  cd Scalaxy
  sbt "project scalaxy-parano" "run examples/Test.scala"
  

• You can also use plain scalac directly, once Scalaxy/Parano's JAR is cached by sbt / Ivy:

  git clone git://github.com/ochafik/Scalaxy.git
  cd Scalaxy
  sbt update
  cd Parano
  scalac -Xplugin:$HOME/.ivy2/cache/com.nativelibs4java/scalaxy-parano_2.10/jars/scalaxy-parano_2.10-0.3-SNAPSHOT.jar examples/Test.scala
  scalac examples/Test.scala