Implement methods

[pfcoperez]

This PR tries to add ImplementMethod transformation aimed to offer a similar functionality to widespread IDEs, e.g:

It works through Selection mechanism as follows:

1. The user selectsa template (mixed template) extended in the definition of another (target template)
2. The transformation finds methods, values and type tags without implementation in the mixed template...
3. ... adding them to the target template as long as they are not implemented in its body.

[wpopielarski]

@pfcoperez looks quite neat, but it needs part on scala-ide part I guess. Let me look at it

[pfcoperez]

Thanks @wpopielarski for taking the time reviewing it! I thought that part would require a new PR, but not to this repo but to https://github.com/scala-ide/scala-ide . If that's the case, I can do it too. My plan is to bring this functionality to https://github.com/ensime/ensime-server too.

[wpopielarski]

Well, these tests are failing

  @Test
  def shouldNotModifyComments() = new FileSet() {
    """
      |package implementMethods
      |
      |trait T {
      |  def t = 42
      |  def f(x: Int): String
      |}
      |
      |object Obj extends /*(*/T/*)*/ { // don't remove this comment
      |}
    """.stripMargin becomes
    """
      |package implementMethods
      |
      |trait T {
      |  def t = 42
      |  def f(x: Int): String
      |}
      |
      |object Obj extends /*(*/T/*)*/ { // don't remove this comment
      |  def f(x: Int): String = {
      |    ???
      |  }
      |}
    """.stripMargin
  } applyRefactoring implementMethods

  @Test
  def implementUnimplementedBackticksEvilMethod() = new FileSet() {
    """
      |package implementMethods
      |
      |trait T {
      |  def `Zła metoda`: Int
      |}
      |
      |object Obj extends /*(*/T/*)*/ {
      |  val doNotCutMeOut = 42
      |}
    """.stripMargin becomes
    """
      |package implementMethods
      |
      |trait T {
      |  def `Zła metoda`: Int
      |}
      |
      |object Obj extends /*(*/T/*)*/ {
      |  val doNotCutMeOut = 42
      |
      |  def `Zła metoda`: Int = {
      |    ???
      |  }
      |}
    """.stripMargin
  } applyRefactoring implementMethods

  @Test
  def implementUnimplementedSpecialMethod() = new FileSet() {
    """
      |package implementMethods
      |
      |trait T {
      |  def :++: : Int
      |}
      |
      |object Obj extends /*(*/T/*)*/ {
      |  val doNotCutMeOut = 42
      |}
    """.stripMargin becomes
    """
      |package implementMethods
      |
      |trait T {
      |  def :++: : Int
      |}
      |
      |object Obj extends /*(*/T/*)*/ {
      |  val doNotCutMeOut = 42
      |
      |  def :++: : Int = {
      |    ???
      |  }
      |}
    """.stripMargin
  } applyRefactoring implementMethods

[wpopielarski]

Generally I think that it will be quite hard to modify trees. The way how you determine unimplemented methods/fields from tree is done OK, but it is safer to modify source code directly, not its tree. There is scala.tools.refactoring.util.Movement util to walk on source. Generally I have to look at this closer.