Scala example source code file (Tags.scala)

This example Scala source code file (Tags.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

analyzer, boolean, compiler, emptytree, list, notype, nsc, position, tag, tree, type, typer

The Tags.scala Scala example source code

package scala.tools.nsc
package typechecker

trait Tags {
  self: Analyzer =>

  import global._
  import definitions._

  trait Tag {
    self: Typer =>

    private val runDefinitions = currentRun.runDefinitions
    import runDefinitions._

    private def resolveTag(pos: Position, taggedTp: Type, allowMaterialization: Boolean) = enteringTyper {
      def wrapper (tree: => Tree): Tree = if (allowMaterialization) (context.withMacrosEnabled[Tree](tree)) else (context.withMacrosDisabled[Tree](tree))
      wrapper(inferImplicit(
        EmptyTree,
        taggedTp,
        reportAmbiguous = true,
        isView = false,
        context,
        saveAmbiguousDivergent = true,
        pos
      ).tree)
    }

    /** Finds in scope or materializes a ClassTag.
     *  Should be used instead of ClassManifest every time compiler needs to persist an erasure.
     *
     *  Once upon a time, we had an `ErasureTag` which was to `ClassTag` the same that `WeakTypeTag` is for `TypeTag`.
     *  However we found out that we don't really need this concept, so it got removed.
     *
     *  @param   pos                    Position for error reporting. Please, provide meaningful value.
     *  @param   tp                     Type we're looking a ClassTag for, e.g. resolveClassTag(pos, IntTpe) will look for ClassTag[Int].
     *  @param   allowMaterialization   If true (default) then the resolver is allowed to launch materialization macros when there's no class tag in scope.
     *                                  If false then materialization macros are prohibited from running.
     *
     *  @returns Tree that represents an `scala.reflect.ClassTag` for `tp` if everything is okay.
     *           EmptyTree if the result contains unresolved (i.e. not spliced) type parameters and abstract type members.
     *           EmptyTree if `allowMaterialization` is false, and there is no class tag in scope.
     */
    def resolveClassTag(pos: Position, tp: Type, allowMaterialization: Boolean = true): Tree = {
      val taggedTp = appliedType(ClassTagClass.typeConstructor, List(tp))
      resolveTag(pos, taggedTp, allowMaterialization)
    }

    /** Finds in scope or materializes an WeakTypeTag (if `concrete` is false) or a TypeTag (if `concrete` is true).
     *
     *  @param   pos                    Position for error reporting. Please, provide meaningful value.
     *  @param   pre                    Prefix that represents a universe this type tag will be bound to.
     *                                  If `pre` is set to `NoType`, then any type tag in scope will do, regardless of its affiliation.
     *                                  If `pre` is set to `NoType`, and tag resolution involves materialization, then `mkRuntimeUniverseRef` will be used.
     *  @param   tp                     Type we're looking a TypeTag for, e.g. resolveTypeTag(pos, mkRuntimeUniverseRef, IntTpe, false) will look for scala.reflect.runtime.universe.TypeTag[Int].
     *  @param   concrete               If true then the result must not contain unresolved (i.e. not spliced) type parameters and abstract type members.
     *                                  If false then the function will always succeed (abstract types will be reified as free types).
     *  @param   allowMaterialization   If true (default) then the resolver is allowed to launch materialization macros when there's no type tag in scope.
     *                                  If false then materialization macros are prohibited from running.
     *
     *  @returns Tree that represents a `scala.reflect.TypeTag` for `tp` if everything is okay.
     *           EmptyTree if `concrete` is true and the result contains unresolved (i.e. not spliced) type parameters and abstract type members.
     *           EmptyTree if `allowMaterialization` is false, and there is no array tag in scope.
     */
    def resolveTypeTag(pos: Position, pre: Type, tp: Type, concrete: Boolean, allowMaterialization: Boolean = true): Tree =
      // if someone requests a type tag, but scala-reflect.jar isn't on the library classpath, then bail
      if (pre == NoType && ApiUniverseClass == NoSymbol) EmptyTree
      else {
        val tagSym = if (concrete) TypeTagClass else WeakTypeTagClass
        val tagTp =  if (pre == NoType) TypeRef(ApiUniverseClass.toTypeConstructor, tagSym, List(tp)) else singleType(pre, pre member tagSym.name)
        val taggedTp = appliedType(tagTp, List(tp))
        resolveTag(pos, taggedTp, allowMaterialization)
      }
  }
}