Introduce MethodTypeKind to quotes reflection API (#20249)

It allows to create Contextual and Implicit MethodTypes. MethodTypeKind
abstracts away the `MethodTypeCompanion` implementation into a simple
enum style choice for a newly added MethodType apply method. The
MethodType unapply is kept as it was for source compatibility, instead
users are encouraged to use `isImplicit` and `isContextual` methods.

Based on #18499 
Fixes #18477

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -2215,6 +2215,12 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
     object MethodType extends MethodTypeModule:
       def apply(paramNames: List[String])(paramInfosExp: MethodType => List[TypeRepr], resultTypeExp: MethodType => TypeRepr): MethodType =
         Types.MethodType(paramNames.map(_.toTermName))(paramInfosExp, resultTypeExp)
+      def apply(kind: MethodTypeKind)(paramNames: List[String])(paramInfosExp: MethodType => List[TypeRepr], resultTypeExp: MethodType => TypeRepr): MethodType =
+        val companion = kind match
+          case MethodTypeKind.Contextual => Types.ContextualMethodType
+          case MethodTypeKind.Implicit => Types.ImplicitMethodType
+          case MethodTypeKind.Plain => Types.MethodType
+        companion.apply(paramNames.map(_.toTermName))(paramInfosExp, resultTypeExp)
       def unapply(x: MethodType): (List[String], List[TypeRepr], TypeRepr) =
         (x.paramNames.map(_.toString), x.paramTypes, x.resType)
     end MethodType
@@ -2223,6 +2229,12 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
       extension (self: MethodType)
         def isErased: Boolean = false
         def isImplicit: Boolean = self.isImplicitMethod
+        def isContextual: Boolean = self.isContextualMethod
+        def methodTypeKind: MethodTypeKind = 
+          self.companion match
+            case Types.ContextualMethodType => MethodTypeKind.Contextual
+            case Types.ImplicitMethodType => MethodTypeKind.Implicit
+            case _ => MethodTypeKind.Plain
         def param(idx: Int): TypeRepr = self.newParamRef(idx)
 
         def erasedParams: List[Boolean] = self.erasedParams

library/src/scala/quoted/Quotes.scala

@@ -211,6 +211,10 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
    *               +- MatchCase
    *               +- TypeBounds
    *               +- NoPrefix
+   * 
+   *  +- MethodTypeKind -+- Contextual
+   *                     +- Implicit
+   *                     +- Plain
    *
    *  +- Selector -+- SimpleSelector
    *               +- RenameSelector
@@ -3234,6 +3238,15 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
     /** `TypeTest` that allows testing at runtime in a pattern match if a `TypeRepr` is a `MethodOrPoly` */
     given MethodOrPolyTypeTest: TypeTest[TypeRepr, MethodOrPoly]
 
+    /** Type which decides on the kind of parameter list represented by `MethodType`. */
+    enum MethodTypeKind:
+      /** Represents a parameter list without any implicitness of parameters, like (x1: X1, x2: X2, ...) */
+      case Plain
+      /** Represents a parameter list with implicit parameters, like `(implicit X1, ..., Xn)`, `(using X1, ..., Xn)`, `(using x1: X1, ..., xn: Xn)` */
+      case Implicit
+      /** Represents a parameter list of a contextual method, like `(using X1, ..., Xn)` or `(using x1: X1, ..., xn: Xn)` */
+      case Contextual
+
     /** Type of the definition of a method taking a single list of parameters. It's return type may be a MethodType. */
     type MethodType <: MethodOrPoly
 
@@ -3246,6 +3259,7 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
     /** Methods of the module object `val MethodType` */
     trait MethodTypeModule { this: MethodType.type =>
       def apply(paramNames: List[String])(paramInfosExp: MethodType => List[TypeRepr], resultTypeExp: MethodType => TypeRepr): MethodType
+      def apply(kind: MethodTypeKind)(paramNames: List[String])(paramInfosExp: MethodType => List[TypeRepr], resultTypeExp: MethodType => TypeRepr): MethodType
       def unapply(x: MethodType): (List[String], List[TypeRepr], TypeRepr)
     }
 
@@ -3255,8 +3269,12 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
     /** Extension methods of `MethodType` */
     trait MethodTypeMethods:
       extension (self: MethodType)
-        /** Is this the type of using parameter clause `(implicit X1, ..., Xn)`, `(using X1, ..., Xn)` or `(using x1: X1, ..., xn: Xn)` */
+        /** Is this the type of parameter clause like `(implicit X1, ..., Xn)`, `(using X1, ..., Xn)` or `(using x1: X1, ..., xn: Xn)` */
         def isImplicit: Boolean
+        /** Is this the type of parameter clause like `(using X1, ..., Xn)` or `(using x1: X1, x2: X2, ... )` */
+        def isContextual: Boolean
+        /** Returns a MethodTypeKind object representing the implicitness of the MethodType parameter clause. */ 
+        def methodTypeKind: MethodTypeKind
         /** Is this the type of erased parameter clause `(erased x1: X1, ..., xn: Xn)` */
         @deprecated("Use `hasErasedParams` and `erasedParams`", "3.4")
         def isErased: Boolean

project/MiMaFilters.scala

@@ -50,7 +50,12 @@ object MiMaFilters {
       // Breaking changes since last reference version
       Build.mimaPreviousDottyVersion -> // Seq.empty, // We should never break backwards compatibility
         Seq(
-          ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#SymbolMethods.isSuperAccessor"), // This change is acceptable. See comment in `Breaking changes since last LTS`.
+          // `ReversedMissingMethodProblem`s are acceptable. See comment in `Breaking changes since last LTS`.
+          ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#SymbolMethods.isSuperAccessor"),
+          ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule.MethodTypeKind"),
+          ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#MethodTypeModule.apply"),
+          ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#MethodTypeMethods.methodTypeKind"),
+          ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#MethodTypeMethods.isContextual"),
         ),
 
       // Breaking changes since last LTS

tests/run-macros/reflect-method-type-kind/macro_1.scala

@@ -0,0 +1,64 @@
+trait Foo
+trait Bar
+
+object Methods:
+  def implicitMethod(implicit foo: Foo, int: Int): Bar = ???
+  def contextualMethod(using foo: Foo, int: Int): Bar = ???
+  def plainMethod(foo: Foo, int: Int): Bar = ???
+
+object Macro:
+  import scala.quoted._
+  inline def macroCall(): Unit = ${ macroCallImpl }
+  def macroCallImpl(using Quotes): Expr[Unit] =
+    testReadingMethodTypeKind
+    testCreatingMethodTypeKind
+    '{()}
+
+  def testReadingMethodTypeKind(using Quotes) =
+    import quotes.reflect._
+    def getFromMethods(name: String): TypeRepr =
+      val typeRepr =  TypeRepr.of[Methods.type]
+      val symbol = 
+        typeRepr.typeSymbol.methodMember(name).headOption.getOrElse(
+          typeRepr.typeSymbol.fieldMember(name)
+        )
+      typeRepr.memberType(symbol)
+
+    assert(getFromMethods("implicitMethod").asInstanceOf[MethodType].isImplicit)
+    assert(!getFromMethods("implicitMethod").asInstanceOf[MethodType].isContextual)
+    assert(getFromMethods("implicitMethod").asInstanceOf[MethodType].methodTypeKind == MethodTypeKind.Implicit)
+
+    assert(getFromMethods("contextualMethod").asInstanceOf[MethodType].isImplicit)
+    assert(getFromMethods("contextualMethod").asInstanceOf[MethodType].isContextual)
+    assert(getFromMethods("contextualMethod").asInstanceOf[MethodType].methodTypeKind == MethodTypeKind.Contextual)
+
+    assert(!getFromMethods("plainMethod").asInstanceOf[MethodType].isImplicit)
+    assert(!getFromMethods("plainMethod").asInstanceOf[MethodType].isContextual)
+    assert(getFromMethods("plainMethod").asInstanceOf[MethodType].methodTypeKind == MethodTypeKind.Plain)
+
+
+  def testCreatingMethodTypeKind(using Quotes) =
+    import quotes.reflect._
+    val paramTypes = List(TypeRepr.of[Foo], TypeRepr.of[Int])
+    val resType = TypeRepr.of[Bar]
+    val implicitMethodType = MethodType.apply(MethodTypeKind.Implicit)(List("foo", "int"))(mt => paramTypes, mt => resType)
+    assert(implicitMethodType.isImplicit)
+    assert(!implicitMethodType.isContextual)
+    assert(implicitMethodType.methodTypeKind == MethodTypeKind.Implicit)
+    assert(implicitMethodType.methodTypeKind != MethodTypeKind.Contextual)
+    assert(implicitMethodType.methodTypeKind != MethodTypeKind.Plain)
+
+
+    val contextualMethodType = MethodType.apply(MethodTypeKind.Contextual)(List("foo", "int"))(mt => paramTypes, mt => resType)
+    assert(contextualMethodType.isImplicit)
+    assert(contextualMethodType.isContextual)
+    assert(contextualMethodType.methodTypeKind != MethodTypeKind.Implicit)
+    assert(contextualMethodType.methodTypeKind == MethodTypeKind.Contextual)
+    assert(contextualMethodType.methodTypeKind != MethodTypeKind.Plain)
+
+    val plainMethodType = MethodType.apply(MethodTypeKind.Plain)(List("foo", "int"))(mt => paramTypes, mt => resType)
+    assert(!plainMethodType.isContextual)
+    assert(!plainMethodType.isImplicit)
+    assert(plainMethodType.methodTypeKind != MethodTypeKind.Implicit)
+    assert(plainMethodType.methodTypeKind != MethodTypeKind.Contextual)
+    assert(plainMethodType.methodTypeKind == MethodTypeKind.Plain)

tests/run-macros/reflect-method-type-kind/test_2.scala

@@ -0,0 +1,3 @@
+object Test:
+  def main(args: Array[String]): Unit =
+    Macro.macroCall()