pabzdzdzwiagief/initialization

A Scala compiler plugin that detects reference-before-assignment errors

initialization

A Scala compiler plugin. Detects code that may run into any of several Scala's initialization order pitfalls. It does not attempt to prevent every possible reference-before-initialization. Still, at least some classes of such errors are covered.

The difference between this and -Xcheckinit compiler switch is that checks are done purely during compilation time. There are no costs incurred at runtime, only a library dependency is brought for necessary metadata.

usage

Add this to your build.sbt:

 autoCompilerPlugins := true

 libraryDependencies += compilerPlugin("com.github.pabzdzdzwiagief" %% "initialization" % "0.11.0-rc.2")

 libraryDependencies += "com.github.pabzdzdzwiagief.initialization" %% "annotation" % "0.11.0-rc.2"

example

// simple.scala

pacakge localhost

class simple {
  m1()
  val v1 = 4

  def m1() {
    println(v1)
  }
}

The code above will generate following warning:

simple.scala:10: warning: value v1 is referenced before assignment
        at localhost.simple.m1(simple.scala:6)
        at localhost.simple.<init>(simple.scala:5)

    println(v1)
            ^

For more examples see src/test/resources/examples/positives/.

limitations

code compiled without the plugin

Initialization problems can be spotted only in the code compiled with the plugin. When e.g. extending a class that comes from some external library, the analysis will loose its track every time a call graph descends to methods defined in that class.

false positives

The plugin may happen to be overreactive. In such cases use standard @unchecked annotation.

pacakge localhost

import util.Random.{nextBoolean => iFeelLucky}

class uncheck {
  (m1() : @unchecked) // no warnings
  val v1 = 4

  def m1() {
    println(if (iFeelLucky) v1 else 4)
  }
}

functions

All functions are always treated as if they were called immediately after being created. The primary reason is handling a quite typical case:

class usageOfForLoop {
  for (i <- 1 to 10) {
    println(notInitialized)
  }

  val notInitialized = 4
}

which uses a compiler-generated function underneath. Tracking down where do functions passed as parameters eventually end up being called requires far broader and more detailed analysis than one the plugin performs.

In some cases changing a function definition to a local method may help:

// change this:
val inc = {(x: Int) => x + 1}

// to this:
def inc(x: Int) = x + 1

and while any later partial application/currying will trigger reference check anyway, it will at least happen in a closer proximity to the actual function call.

test cases

To add a test case, put a file in src/test/resources/positives/ directory (or in negatives/ for tests with no compilation warnings expected) with the following format:

// [one-line title of the test case]

package localhost

[scala code to compile]

// [expected compilation messages, with one-space margin]
//
//

to have it automatically picked up when tests are executed.

license

BSD 2-Clause