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AirSpec: A Functional Testing Framework for Scala
There is a newer version: 24.9.0
/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package wvlet.airframe

import java.util.concurrent.ConcurrentHashMap

import wvlet.airframe.surface.Surface
import wvlet.log.LogSupport

import scala.language.implicitConversions
import scala.annotation.experimental
import wvlet.airframe.DISupport

/**
  * The entry point to create a new design beginning from a blanc design  import wvlet.airframe._
  *
  * val d = design.bind[X] 
  */
def newDesign: Design = Design.empty

/**
  * Create an empty design, which sends life cycle logs to debug log level
  */
def newSilentDesign: Design = newDesign.noLifeCycleLogging

import scala.jdk.CollectionConverters.*

// This will not be used in Scala 3, but left for the compatibility with Scala 2
val traitFactoryCache = new ConcurrentHashMap[Surface, Session => Any].asScala

def getOrElseUpdateTraitFactoryCache(s: Surface, factory: Session => Any): Session => Any =
  traitFactoryCache.getOrElseUpdate(s, factory)

@deprecated("Instantiating trait is still experimental in Scala 3.3.1", "23.9.1")
inline def registerTraitFactory[A]: Unit = {
  // registerTraitFactoryImpl[A]
}

import scala.quoted.*

private def shouldGenerateTrait[A](using
    tpe: Type[A],
    q: Quotes
): Boolean =
  import quotes.*
  import quotes.reflect.*

  val t = TypeRepr.of[A]
  val a = t.typeSymbol

  // Find the public default constructor that has no arguments
  val hasPublicDefaultConstructor: Boolean =
    val pc = a.primaryConstructor
    pc.paramSymss.size == 1 && pc.paramSymss(0).size == 0

  val hasAbstractMethods: Boolean =
    a.methodMembers.exists { x =>
      x.flags.is(Flags.Method) &&
      (x.flags.is(Flags.Abstract) || x.flags.is(Flags.Deferred))
    }
  val isTaggedType = a.fullName.startsWith("wvlet.airframe.surface.tag.")
  val isSealedType = a.flags.is(Flags.Sealed)
  val isStatic     = a.flags.is(Flags.JavaStatic)
  val isLocal      = a.flags.is(Flags.Local)
  val isTrait      = a.flags.is(Flags.Trait)

  val shouldInstantiateTrait =
    if !isStatic then
      // = Non static type
      // If X is non static type (= local class or trait),
      // we need to instantiate it first in order to populate its $outer variables

      // We cannot instantiate path-dependent types
      if a.fullName.contains("#") then false
      else !hasAbstractMethods && hasPublicDefaultConstructor
    else if a.isAbstractType then
      // = Abstract type
      // We cannot build abstract type X that has abstract methods, so bind[X].to[ConcreteType]
      // needs to be found in the design

      // If there is no abstract methods, it might be a trait without any method
      !hasAbstractMethods
    else
      // We cannot instantiate any trait or class without the default constructor
      // So binding needs to be found in the Design.
      hasPublicDefaultConstructor

  // Tagged type or sealed class binding should be found in Design
  val result = isTrait && !isTaggedType && !isSealedType && shouldInstantiateTrait

  // println(s"${a.flags.show}, isStatic: ${isStatic}, isAbstract: ${a.isAbstractType}, isSealed: ${isSealedType} ${a.fullName}, " +
  //  s"has pstr: ${hasPublicDefaultConstructor} is tagged: ${isTaggedType}, has abstract method: ${hasAbstractMethods}")

  result

@experimental def registerTraitFactoryImpl[A](using
    tpe: Type[A],
    q: Quotes
): quoted.Expr[Unit] =
  import quotes.*
  import quotes.reflect.*

  if !shouldGenerateTrait[A] then '{}
  else
    val name    = "$anon"
    val parents = List(TypeTree.of[Object], TypeTree.of[A], TypeTree.of[DISupport])

    def decls(cls: Symbol): List[Symbol] =
      List(Symbol.newMethod(cls, "session", MethodType(Nil)(_ => Nil, _ => TypeRepr.of[Session])))

    val cls = Symbol.newClass(Symbol.spliceOwner, name, parents = parents.map(_.tpe), decls, selfType = None)
    val sessionMethodSym          = cls.declaredMethod("session").head
    def sessionMethodDef(s: Term) = DefDef(sessionMethodSym, argss => Some(s))
    def newCls(s: Term) =
      val clsDef = ClassDef(cls, parents, body = List(sessionMethodDef(s)))
      val newCls = Typed(Apply(Select(New(TypeIdent(cls)), cls.primaryConstructor), Nil), TypeTree.of[A])
      Block(List(clsDef), newCls)

    // Generate code { (s: Session) => new A with DISupport { def sesion: Session = s } }
    val body = Lambda(
      owner = Symbol.spliceOwner,
      tpe = MethodType(List("s"))(_ => List(TypeRepr.of[Session]), _ => TypeRepr.of[A]),
      rhsFn = (sym: Symbol, paramRefs: List[Tree]) =>
        val s  = paramRefs.head.asExprOf[Session].asTerm
        val fn = newCls(s)
        fn.changeOwner(sym)
    )
    // Register trait factory
    // { (s: Session) => new A with DISupport { def session = s } }
    '{
      wvlet.airframe.getOrElseUpdateTraitFactoryCache(
        Surface.of[A],
        ${
          body.asExprOf[Session => Any]
        }
      )
    }