Scala example source code file (Enclosures.scala)

This example Scala source code file (Enclosures.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

apis, class, compilationunit, couldn't, enclosureexception, enclosures, list, position, run, tree

The Enclosures.scala Scala example source code

package scala
package reflect
package macros

import scala.language.existentials // SI-6541

/**
 * <span class="badge badge-red" style="float: right;">EXPERIMENTAL</span>
 *
 *  A slice of [[scala.reflect.macros.blackbox.Context the Scala macros context]] that exposes
 *  enclosing trees (method, class, compilation unit and currently compiled macro application),
 *  the enclosing position of the macro expansion, as well as macros and implicits
 *  that are currently in-flight.
 *
 *  Starting from Scala 2.11.0, the APIs to get the trees enclosing by the current macro application are deprecated,
 *  and the reasons for that are two-fold. Firstly, we would like to move towards the philosophy of locally-expanded macros,
 *  as it has proven to be important for understanding of code. Secondly, within the current architecture of scalac,
 *  we are unable to have c.enclosingTree-style APIs working robustly. Required changes to the typechecker would greatly
 *  exceed the effort that we would like to expend on this feature given the existence of more pressing concerns at the moment.
 *  This is somewhat aligned with the overall evolution of macros during the 2.11 development cycle, where we played with
 *  `c.introduceTopLevel` and `c.introduceMember`, but at the end of the day decided to reject them.
 *
 *  If you're relying on the now deprecated APIs, consider using the new [[c.internal.enclosingOwner]] method that can be used to obtain
 *  the names of enclosing definitions. Alternatively try reformulating your macros in terms of completely local expansion
 *  and/or joining a discussion of a somewhat related potential language feature at [[https://groups.google.com/forum/#!topic/scala-debate/f4CLmYShX6Q]].
 *  We also welcome questions and suggestions on our mailing lists, where we would be happy to further discuss this matter.
 */
trait Enclosures {
  self: blackbox.Context =>

  /** The tree that undergoes macro expansion.
   *  Can be useful to get an offset or a range position of the entire tree being processed.
   */
  def macroApplication: Tree

  /** Contexts that represent macros in-flight, including the current one. Very much like a stack trace, but for macros only.
   *  Can be useful for interoperating with other macros and for imposing compiler-friendly limits on macro expansion.
   *
   *  Is also priceless for emitting sane error messages for macros that are called by other macros on synthetic (i.e. position-less) trees.
   *  In that dire case navigate the `enclosingMacros` stack, and it will most likely contain at least one macro with a position-ful macro application.
   *  See `enclosingPosition` for a default implementation of this logic.
   *
   *  Unlike `openMacros`, this is a val, which means that it gets initialized when the context is created
   *  and always stays the same regardless of whatever happens during macro expansion.
   */
  def enclosingMacros: List[blackbox.Context]

  /** Tries to guess a position for the enclosing application.
   *  But that is simple, right? Just dereference `pos` of `macroApplication`? Not really.
   *  If we're in a synthetic macro expansion (no positions), we must do our best to infer the position of something that triggerd this expansion.
   *  Surprisingly, quite often we can do this by navigation the `enclosingMacros` stack.
   */
  def enclosingPosition: Position

  /** Tree that corresponds to the enclosing method, or EmptyTree if not applicable.
   *  @see [[scala.reflect.macros.Enclosures]]
   */
  @deprecated("c.enclosingTree-style APIs are now deprecated; consult the scaladoc for more information", "2.11.0")
  def enclosingMethod: Tree

  /** Tree that corresponds to the enclosing class, or EmptyTree if not applicable.
   *  @see [[scala.reflect.macros.Enclosures]]
   */
  @deprecated("c.enclosingTree-style APIs are now deprecated; consult the scaladoc for more information", "2.11.0")
  def enclosingClass: Tree

  /** Tree that corresponds to the enclosing DefDef tree.
   *  Throws `EnclosureException` if there's no such enclosing tree.
   *  @see [[scala.reflect.macros.Enclosures]]
   */
  @deprecated("c.enclosingTree-style APIs are now deprecated; consult the scaladoc for more information", "2.11.0")
  def enclosingDef: universe.DefDef

  /** Tree that corresponds to the enclosing Template tree.
   *  Throws `EnclosureException` if there's no such enclosing tree.
   *  @see [[scala.reflect.macros.Enclosures]]
   */
  @deprecated("c.enclosingTree-style APIs are now deprecated; consult the scaladoc for more information", "2.11.0")
  def enclosingTemplate: universe.Template

  /** Tree that corresponds to the enclosing ImplDef tree (i.e. either ClassDef or ModuleDef).
   *  Throws `EnclosureException` if there's no such enclosing tree.
   *  @see [[scala.reflect.macros.Enclosures]]
   */
  @deprecated("c.enclosingTree-style APIs are now deprecated; consult the scaladoc for more information", "2.11.0")
  def enclosingImpl: universe.ImplDef

  /** Tree that corresponds to the enclosing PackageDef tree.
   *  Throws `EnclosureException` if there's no such enclosing tree.
   *  @see [[scala.reflect.macros.Enclosures]]
   */
  @deprecated("c.enclosingTree-style APIs are now deprecated; consult the scaladoc for more information", "2.11.0")
  def enclosingPackage: universe.PackageDef

  /** Compilation unit that contains this macro application.
   *  @see [[scala.reflect.macros.Enclosures]]
   */
  @deprecated("c.enclosingTree-style APIs are now deprecated; consult the scaladoc for more information", "2.11.0")
  def enclosingUnit: CompilationUnit

  /** Compilation run that contains this macro application.
   *  @see [[scala.reflect.macros.Enclosures]]
   */
  @deprecated("c.enclosingTree-style APIs are now deprecated; consult the scaladoc for more information", "2.11.0")
  def enclosingRun: Run

  /** Indicates than one of the enclosure methods failed to find a tree
   *  of required type among enclosing trees.
   *  @see [[scala.reflect.macros.Enclosures]]
   */
  @deprecated("c.enclosingTree-style APIs are now deprecated; consult the scaladoc for more information", "2.11.0")
  case class EnclosureException(expected: Class[_], enclosingTrees: List[Tree])
  extends Exception(s"Couldn't find a tree of type $expected among enclosing trees $enclosingTrees")
}