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scala3-library-bootstrappedJS
// TODO in which package should this class be located?
package scala
package annotation
import scala.quoted.*
/** Base trait for macro annotation implementation.
* Macro annotations can transform definitions and add new definitions.
*
* See: `MacroAnnotation.transform`
*
* @syntax markdown
*/
@experimental
trait MacroAnnotation extends StaticAnnotation:
/** Transform the `tree` definition and add new definitions
*
* This method takes as argument the annotated definition.
* It returns a non-empty list containing the modified version of the annotated definition.
* The new tree for the definition must use the original symbol.
* New definitions can be added to the list before or after the transformed definitions, this order
* will be retained. New definitions will not be visible from outside the macro expansion.
*
* #### Restrictions
* - All definitions in the result must have the same owner. The owner can be recovered from `Symbol.spliceOwner`.
* - Special case: an annotated top-level `def`, `val`, `var`, `lazy val` can return a `class`/`object`
* definition that is owned by the package or package object.
* - Can not return a `type`.
* - Annotated top-level `class`/`object` can not return top-level `def`, `val`, `var`, `lazy val`.
* - Can not see new definition in user written code.
*
* #### Good practices
* - Make your new definitions private if you can.
* - New definitions added as class members should use a fresh name (`Symbol.freshName`) to avoid collisions.
* - New top-level definitions should use a fresh name (`Symbol.freshName`) that includes the name of the annotated
* member as a prefix to avoid collisions of definitions added in other files.
*
* **IMPORTANT**: When developing and testing a macro annotation, you must enable `-Xcheck-macros` and `-Ycheck:all`.
*
* #### Example 1
* This example shows how to modify a `def` and add a `val` next to it using a macro annotation.
* ```scala
* import scala.quoted.*
* import scala.collection.concurrent
*
* class memoize extends MacroAnnotation:
* def transform(using Quotes)(
* definition: quotes.reflect.Definition,
* companion: Option[quotes.reflect.Definition]
* ): List[quotes.reflect.Definition] =
* import quotes.reflect.*
* definition match
* case DefDef(name, TermParamClause(param :: Nil) :: Nil, tpt, Some(rhsTree)) =>
* (param.tpt.tpe.asType, tpt.tpe.asType) match
* case ('[t], '[u]) =>
* val cacheName = Symbol.freshName(name + "Cache")
* val cacheSymbol = Symbol.newVal(Symbol.spliceOwner, cacheName, TypeRepr.of[concurrent.Map[t, u]], Flags.Private, Symbol.noSymbol)
* val cacheRhs =
* given Quotes = cacheSymbol.asQuotes
* '{ concurrent.TrieMap.empty[t, u] }.asTerm
* val cacheVal = ValDef(cacheSymbol, Some(cacheRhs))
* val newRhs =
* given Quotes = definition.symbol.asQuotes
* val cacheRefExpr = Ref(cacheSymbol).asExprOf[concurrent.Map[t, u]]
* val paramRefExpr = Ref(param.symbol).asExprOf[t]
* val rhsExpr = rhsTree.asExprOf[u]
* '{ $cacheRefExpr.getOrElseUpdate($paramRefExpr, $rhsExpr) }.asTerm
* val newTree = DefDef.copy(definition)(name, TermParamClause(param :: Nil) :: Nil, tpt, Some(newRhs))
* List(cacheVal, newTree)
* case _ =>
* report.error("Annotation only supported on `def` with a single argument are supported")
* List(definition)
* end transform
* ```
* with this macro annotation a user can write
* ```scala
* //{
* class memoize extends scala.annotation.StaticAnnotation
* //}
* @memoize
* def fib(n: Int): Int =
* println(s"compute fib of $n")
* if n <= 1 then n else fib(n - 1) + fib(n - 2)
* ```
* and the macro will modify the definition to create
* ```scala
* val fibCache$macro$1 =
* scala.collection.concurrent.TrieMap.empty[Int, Int]
* def fib(n: Int): Int =
* fibCache$macro$1.getOrElseUpdate(
* n,
* {
* println(s"compute fib of $n")
* if n <= 1 then n else fib(n - 1) + fib(n - 2)
* }
* )
* ```
*
* #### Example 2
* This example shows how to modify a `class` using a macro annotation.
* It shows how to override inherited members and add new ones.
* ```scala
* import scala.annotation.{experimental, MacroAnnotation}
* import scala.quoted.*
*
* @experimental
* class equals extends MacroAnnotation:
* def transform(using Quotes)(
* definition: quotes.reflect.Definition,
* companion: Option[quotes.reflect.Definition]
* ): List[quotes.reflect.Definition] =
* import quotes.reflect.*
* definition match
* case ClassDef(className, ctr, parents, self, body) =>
* val cls = definition.symbol
*
* val constructorParameters = ctr.paramss.collect { case clause: TermParamClause => clause }
* if constructorParameters.size != 1 || constructorParameters.head.params.isEmpty then
* report.errorAndAbort("@equals class must have a single argument list with at least one argument", ctr.pos)
* def checkNotOverridden(sym: Symbol): Unit =
* if sym.overridingSymbol(cls).exists then
* report.error(s"Cannot override ${sym.name} in a @equals class")
*
* val fields = body.collect {
* case vdef: ValDef if vdef.symbol.flags.is(Flags.ParamAccessor) =>
* Select(This(cls), vdef.symbol).asExpr
* }
*
* val equalsSym = Symbol.requiredMethod("java.lang.Object.equals")
* checkNotOverridden(equalsSym)
* val equalsOverrideSym = Symbol.newMethod(cls, "equals", equalsSym.info, Flags.Override, Symbol.noSymbol)
* def equalsOverrideDefBody(argss: List[List[Tree]]): Option[Term] =
* given Quotes = equalsOverrideSym.asQuotes
* cls.typeRef.asType match
* case '[c] =>
* Some(equalsExpr[c](argss.head.head.asExpr, fields).asTerm)
* val equalsOverrideDef = DefDef(equalsOverrideSym, equalsOverrideDefBody)
*
* val hashSym = Symbol.newVal(cls, Symbol.freshName("hash"), TypeRepr.of[Int], Flags.Private | Flags.Lazy, Symbol.noSymbol)
* val hashVal = ValDef(hashSym, Some(hashCodeExpr(className, fields)(using hashSym.asQuotes).asTerm))
*
* val hashCodeSym = Symbol.requiredMethod("java.lang.Object.hashCode")
* checkNotOverridden(hashCodeSym)
* val hashCodeOverrideSym = Symbol.newMethod(cls, "hashCode", hashCodeSym.info, Flags.Override, Symbol.noSymbol)
* val hashCodeOverrideDef = DefDef(hashCodeOverrideSym, _ => Some(Ref(hashSym)))
*
* val newBody = equalsOverrideDef :: hashVal :: hashCodeOverrideDef :: body
* List(ClassDef.copy(definition)(className, ctr, parents, self, newBody))
* case _ =>
* report.error("Annotation only supports `class`")
* List(definition)
* end transform
*
* private def equalsExpr[T: Type](that: Expr[Any], thisFields: List[Expr[Any]])(using Quotes): Expr[Boolean] =
* '{
* $that match
* case that: T @unchecked =>
* ${
* val thatFields: List[Expr[Any]] =
* import quotes.reflect.*
* thisFields.map(field => Select('{that}.asTerm, field.asTerm.symbol).asExpr)
* thisFields.zip(thatFields)
* .map { case (thisField, thatField) => '{ $thisField == $thatField } }
* .reduce { case (pred1, pred2) => '{ $pred1 && $pred2 } }
* }
* case _ => false
* }
*
* private def hashCodeExpr(className: String, thisFields: List[Expr[Any]])(using Quotes): Expr[Int] =
* '{
* var acc: Int = ${ Expr(scala.runtime.Statics.mix(-889275714, className.hashCode)) }
* ${
* Expr.block(
* thisFields.map {
* case '{ $field: Boolean } => '{ if $field then 1231 else 1237 }
* case '{ $field: Byte } => '{ $field.toInt }
* case '{ $field: Char } => '{ $field.toInt }
* case '{ $field: Short } => '{ $field.toInt }
* case '{ $field: Int } => field
* case '{ $field: Long } => '{ scala.runtime.Statics.longHash($field) }
* case '{ $field: Double } => '{ scala.runtime.Statics.doubleHash($field) }
* case '{ $field: Float } => '{ scala.runtime.Statics.floatHash($field) }
* case '{ $field: Null } => '{ 0 }
* case '{ $field: Unit } => '{ 0 }
* case field => '{ scala.runtime.Statics.anyHash($field) }
* }.map(hash => '{ acc = scala.runtime.Statics.mix(acc, $hash) }),
* '{ scala.runtime.Statics.finalizeHash(acc, ${Expr(thisFields.size)}) }
* )
* }
* }
* ```
* with this macro annotation a user can write
* ```scala
* //{
* class equals extends scala.annotation.StaticAnnotation
* //}
* @equals class User(val name: String, val id: Int)
* ```
* and the macro will modify the class definition to generate the following code
* ```scala
* class User(val name: String, val id: Int):
* override def equals(that: Any): Boolean =
* that match
* case that: User => this.name == that.name && this.id == that.id
* case _ => false
* private lazy val hash$macro$1: Int =
* var acc = 515782504 // scala.runtime.Statics.mix(-889275714, "User".hashCode)
* acc = scala.runtime.Statics.mix(acc, scala.runtime.Statics.anyHash(name))
* acc = scala.runtime.Statics.mix(acc, id)
* scala.runtime.Statics.finalizeHash(acc, 2)
* override def hashCode(): Int = hash$macro$1
* ```
*
* @param Quotes Implicit instance of Quotes used for tree reflection
* @param definition Tree that will be transformed
* @param companion Tree for the companion class or module if the definition is respectively a module or a class
*
* @syntax markdown
*/
def transform(using Quotes)(definition: quotes.reflect.Definition, companion: Option[quotes.reflect.Definition]): List[quotes.reflect.Definition]
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