Scala example source code file (Typers.scala)

This example Scala source code file (Typers.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

boolean, position, reflection, string, termmode, tree, type, typecheckexception, typecheckmode, typemode, use

The Typers.scala Scala example source code

package scala
package reflect
package macros

import scala.reflect.internal.{Mode => InternalMode}

/**
 * <span class="badge badge-red" style="float: right;">EXPERIMENTAL</span>
 *
 *  A slice of [[scala.reflect.macros.blackbox.Context the Scala macros context]] that
 *  partially exposes the type checker to macro writers.
 */
trait Typers {
  self: blackbox.Context =>

  /** 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 `openMacros` 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 `enclosingMacros`, this is a def, which means that it gets recalculated on every invocation,
   *  so it might change depending on what is going on during macro expansion.
   */
  def openMacros: List[blackbox.Context]

  /** Represents mode of operations of the typechecker underlying `c.typecheck` calls.
   *  Is necessary since the shape of the typechecked tree alone is not enough to guess how it should be typechecked.
   *  Can be EXPRmode (typecheck as a term), TYPEmode (typecheck as a type) or PATTERNmode (typecheck as a pattern).
   */
  // I'd very much like to make use of https://github.com/dsl-paradise/dsl-paradise here!
  type TypecheckMode

  /** Indicates that an argument to `c.typecheck` should be typechecked as a term.
   *  This is the default typechecking mode in Scala 2.11 and the only one supported in Scala 2.10.
   */
  val TERMmode: TypecheckMode

  /** Indicates that an argument to `c.typecheck` should be typechecked as a type.
   */
  val TYPEmode: TypecheckMode

  /** Indicates that an argument to `c.typecheck` should be typechecked as a pattern.
   */
  val PATTERNmode: TypecheckMode

  /** @see `scala.reflect.macros.TypecheckException`
   */
  type TypecheckException = scala.reflect.macros.TypecheckException

  /** @see `scala.reflect.macros.TypecheckException`
   */
  val TypecheckException = scala.reflect.macros.TypecheckException

  /** @see `Typers.typecheck`
   */
  @deprecated("Use `c.typecheck` instead", "2.11.0")
  def typeCheck(tree: Tree, pt: Type = universe.WildcardType, silent: Boolean = false, withImplicitViewsDisabled: Boolean = false, withMacrosDisabled: Boolean = false): Tree =
    typecheck(tree, TERMmode, pt, silent, withImplicitViewsDisabled, withMacrosDisabled)

  /** Typechecks the provided tree against the expected type `pt` in the macro callsite context
   *  under typechecking mode specified in `mode` with [[EXPRmode]] being default.
   *  This populates symbols and types of the tree and possibly transforms it to reflect certain desugarings.
   *
   *  If `silent` is false, `TypecheckException` will be thrown in case of a typecheck error.
   *  If `silent` is true, the typecheck is silent and will return `EmptyTree` if an error occurs.
   *  Such errors don't vanish and can be inspected by turning on -Ymacro-debug-verbose.
   *  Unlike in `inferImplicitValue` and `inferImplicitView`, `silent` is false by default.
   *
   *  Typechecking can be steered with the following optional parameters:
   *    `withImplicitViewsDisabled` recursively prohibits implicit views (though, implicit vals will still be looked up and filled in), default value is false
   *    `withMacrosDisabled` recursively prohibits macro expansions and macro-based implicits, default value is false
   *
   *  @throws [[scala.reflect.macros.TypecheckException]]
   */
  def typecheck(tree: Tree, mode: TypecheckMode = TERMmode, pt: Type = universe.WildcardType, silent: Boolean = false, withImplicitViewsDisabled: Boolean = false, withMacrosDisabled: Boolean = false): Tree

  /** Infers an implicit value of the expected type `pt` in the macro callsite context.
   *  Optional `pos` parameter provides a position that will be associated with the implicit search.
   *
   *  If `silent` is false, `TypecheckException` will be thrown in case of an inference error.
   *  If `silent` is true, the typecheck is silent and will return `EmptyTree` if an error occurs.
   *  Such errors don't vanish and can be inspected by turning on -Xlog-implicits.
   *  Unlike in `typecheck`, `silent` is true by default.
   *
   *  @throws [[scala.reflect.macros.TypecheckException]]
   */
  def inferImplicitValue(pt: Type, silent: Boolean = true, withMacrosDisabled: Boolean = false, pos: Position = enclosingPosition): Tree

  /** Infers an implicit view from the provided tree `tree` of the type `from` to the type `to` in the macro callsite context.
   *  Optional `pos` parameter provides a position that will be associated with the implicit search.
   *
   *  If `silent` is false, `TypecheckException` will be thrown in case of an inference error.
   *  If `silent` is true, the typecheck is silent and will return `EmptyTree` if an error occurs.
   *  Such errors don't vanish and can be inspected by turning on -Xlog-implicits.
   *  Unlike in `typecheck`, `silent` is true by default.
   *
   *  @throws [[scala.reflect.macros.TypecheckException]]
   */
  def inferImplicitView(tree: Tree, from: Type, to: Type, silent: Boolean = true, withMacrosDisabled: Boolean = false, pos: Position = enclosingPosition): Tree

  /** Recursively resets locally defined symbols and types in a given tree.
   *  WARNING: Don't use this API, go for [[untypecheck]] instead.
   */
  @deprecated("Use `c.untypecheck` instead", "2.11.0")
  def resetLocalAttrs(tree: Tree): Tree

  /** In the current implementation of Scala's reflection API, untyped trees (also known as parser trees or unattributed trees)
   *  are observationally different from typed trees (also known as typer trees, typechecked trees or attributed trees),
   *
   *  Usually, if some compiler API takes a tree, then both untyped and typed trees will do. However in some cases,
   *  only untyped or only typed trees are appropriate. For example, [[eval]] only accepts untyped trees and one can only splice
   *  typed trees inside typed trees. Therefore in the current reflection API, there is a need in functions
   *  that go back and forth between untyped and typed trees. For this we have [[typecheck]] and `untypecheck`.
   *
   *  Note that `untypecheck` is currently afflicted by https://issues.scala-lang.org/browse/SI-5464,
   *  which makes it sometimes corrupt trees so that they don't make sense anymore. Unfortunately, there's no workaround for that.
   *  We plan to fix this issue soon, but for now please keep it in mind.
   *
   *  @see [[http://stackoverflow.com/questions/20936509/scala-macros-what-is-the-difference-between-typed-aka-typechecked-an-untyped]]
   */
  def untypecheck(tree: Tree): Tree
}

/** Indicates an error during one of the methods in [[scala.reflect.macros.Typers]].
 */
case class TypecheckException(pos: scala.reflect.api.Position, msg: String) extends Exception(msg)