Add defn.FunctionNOf.{apply,unapply}

This provides variant to `defn.FunctionOf` that only deals with proper
`FunctionN` and `ContextFunctionN` types. This avoids some overhead. A
difference between the two `unapply`s is that this one does not dealias
the type, it needs to be dealiased at call site.

Part of #18305

[Cherry-picked d78c157][modified]

Author: WojciechMazur

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -1102,10 +1102,8 @@ class Definitions {
   object FunctionOf {
     def apply(args: List[Type], resultType: Type, isContextual: Boolean = false)(using Context): Type =
       val mt = MethodType.companion(isContextual, false)(args, resultType)
-      if mt.hasErasedParams then
-        RefinedType(ErasedFunctionClass.typeRef, nme.apply, mt)
-      else
-        FunctionType(args.length, isContextual).appliedTo(args ::: resultType :: Nil)
+      if mt.hasErasedParams then RefinedType(ErasedFunctionClass.typeRef, nme.apply, mt)
+      else FunctionNOf(args, resultType, isContextual)
     def unapply(ft: Type)(using Context): Option[(List[Type], Type, Boolean)] = {
       ft.dealias match
         case ErasedFunctionOf(mt) =>
@@ -1132,6 +1130,24 @@ class Definitions {
       case _ => None
   }
 
+   object FunctionNOf {
+    /** Create a `FunctionN` or `ContextFunctionN` type applied to the arguments and result type */
+    def apply(args: List[Type], resultType: Type, isContextual: Boolean = false)(using Context): Type =
+      FunctionType(args.length, isContextual).appliedTo(args ::: resultType :: Nil)
+
+    /** Matches a (possibly aliased) `FunctionN[...]` or `ContextFunctionN[...]`.
+     *  Extracts the list of function argument types, the result type and whether function is contextual.
+     */
+    def unapply(tpe: Type)(using Context): Option[(List[Type], Type, Boolean)] = {
+      val tsym = tpe.typeSymbol
+      if isFunctionSymbol(tsym) && tpe.isRef(tsym) then
+        val targs = tpe.argInfos
+        if (targs.isEmpty) None
+        else Some(targs.init, targs.last, tsym.name.isContextFunction)
+      else None
+    }
+  }
+
   object RefinedFunctionOf {
     /** Matches a refined `PolyFunction`/`FunctionN[...]`/`ContextFunctionN[...]`.
      *  Extracts the method type type and apply info.

compiler/src/dotty/tools/dotc/core/TypeErasure.scala

@@ -932,7 +932,7 @@ class TypeErasure(sourceLanguage: SourceLanguage, semiEraseVCs: Boolean, isConst
       case tp: TermRef =>
         sigName(underlyingOfTermRef(tp))
       case ExprType(rt) =>
-        sigName(defn.FunctionOf(Nil, rt))
+        sigName(defn.FunctionNOf(Nil, rt))
       case tp: TypeVar if !tp.isInstantiated =>
         tpnme.Uninstantiated
       case tp @ defn.PolyOrErasedFunctionOf(_) =>

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1874,7 +1874,7 @@ object Types {
           case res: MethodType => res.toFunctionType(isJava)
           case res => res
         }
-        val funType = defn.FunctionOf(
+        val funType = defn.FunctionNOf(
            mt.paramInfos.mapConserve(_.translateFromRepeated(toArray = isJava)),
           result1, isContextual)
         if alwaysDependent || mt.isResultDependent then

compiler/src/dotty/tools/dotc/transform/PickleQuotes.scala

@@ -326,7 +326,7 @@ object PickleQuotes {
               defn.QuotedExprClass.typeRef.appliedTo(defn.AnyType)),
             args =>
               val cases = holeContents.zipWithIndex.map { case (splice, idx) =>
-                val defn.FunctionOf(argTypes, defn.FunctionOf(quotesType :: _, _, _), _) = splice.tpe: @unchecked
+                val defn.FunctionNOf(argTypes, defn.FunctionNOf(quotesType :: _, _, _), _) = splice.tpe: @unchecked
                 val rhs = {
                   val spliceArgs = argTypes.zipWithIndex.map { (argType, i) =>
                     args(1).select(nme.apply).appliedTo(Literal(Constant(i))).asInstance(argType)

compiler/src/dotty/tools/dotc/transform/SpecializeFunctions.scala

@@ -88,7 +88,7 @@ class SpecializeFunctions extends MiniPhase {
                   // Need to cast to regular function, since specialized apply methods
                   // are not members of ContextFunction0. The cast will be eliminated in
                   // erasure.
-                  qual.cast(defn.FunctionOf(Nil, res))
+                  qual.cast(defn.FunctionNOf(Nil, res))
                 case _ =>
                   qual
               qual1.select(specializedApply)

compiler/src/dotty/tools/dotc/transform/TreeChecker.scala

@@ -728,9 +728,9 @@ object TreeChecker {
         if isTerm then defn.QuotedExprClass.typeRef.appliedTo(tree1.typeOpt)
         else defn.QuotedTypeClass.typeRef.appliedTo(tree1.typeOpt)
       val contextualResult =
-        defn.FunctionOf(List(defn.QuotesClass.typeRef), expectedResultType, isContextual = true)
+        defn.FunctionNOf(List(defn.QuotesClass.typeRef), expectedResultType, isContextual = true)
       val expectedContentType =
-        defn.FunctionOf(argQuotedTypes, contextualResult)
+        defn.FunctionNOf(argQuotedTypes, contextualResult)
       assert(content.typeOpt =:= expectedContentType, i"unexpected content of hole\nexpected: ${expectedContentType}\nwas: ${content.typeOpt}")
 
       tree1

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -1717,7 +1717,7 @@ trait Applications extends Compatibility {
           def apply(t: Type) = t match {
             case t @ AppliedType(tycon, args) =>
               def mapArg(arg: Type, tparam: TypeParamInfo) =
-                if (variance > 0 && tparam.paramVarianceSign < 0) defn.FunctionOf(arg :: Nil, defn.UnitType)
+                if (variance > 0 && tparam.paramVarianceSign < 0) defn.FunctionNOf(arg :: Nil, defn.UnitType)
                 else arg
               mapOver(t.derivedAppliedType(tycon, args.zipWithConserve(tycon.typeParams)(mapArg)))
             case _ => mapOver(t)
@@ -1944,7 +1944,7 @@ trait Applications extends Compatibility {
     /** The shape of given tree as a type; cannot handle named arguments. */
     def typeShape(tree: untpd.Tree): Type = tree match {
       case untpd.Function(args, body) =>
-        defn.FunctionOf(
+        defn.FunctionNOf(
           args.map(Function.const(defn.AnyType)), typeShape(body),
           isContextual = untpd.isContextualClosure(tree))
       case Match(EmptyTree, _) =>
@@ -1984,8 +1984,8 @@ trait Applications extends Compatibility {
         def paramCount(ref: TermRef) =
           val formals = ref.widen.firstParamTypes
           if formals.length > idx then
-            formals(idx) match
-              case defn.FunctionOf(args, _, _) => args.length
+            formals(idx).dealias match
+              case defn.FunctionNOf(args, _, _) => args.length
               case _ => -1
           else -1
 
@@ -2070,8 +2070,8 @@ trait Applications extends Compatibility {
           else resolveMapped(alts1, _.widen.appliedTo(targs1.tpes), pt1)
 
       case pt =>
-        val compat0 = pt match
-          case defn.FunctionOf(args, resType, _) =>
+        val compat0 = pt.dealias match
+          case defn.FunctionNOf(args, resType, _) =>
             narrowByTypes(alts, args, resType)
           case _ =>
             Nil
@@ -2260,7 +2260,7 @@ trait Applications extends Compatibility {
               false
           val commonFormal =
             if (isPartial) defn.PartialFunctionOf(commonParamTypes.head, WildcardType)
-            else defn.FunctionOf(commonParamTypes, WildcardType, isContextual = untpd.isContextualClosure(arg))
+            else defn.FunctionNOf(commonParamTypes, WildcardType, isContextual = untpd.isContextualClosure(arg))
           overload.println(i"pretype arg $arg with expected type $commonFormal")
           if (commonParamTypes.forall(isFullyDefined(_, ForceDegree.flipBottom)))
             withMode(Mode.ImplicitsEnabled) {

compiler/src/dotty/tools/dotc/typer/ProtoTypes.scala

@@ -371,9 +371,9 @@ object ProtoTypes {
     def allArgTypesAreCurrent()(using Context): Boolean =
       state.typedArg.size == args.length
 
-    private def isUndefined(tp: Type): Boolean = tp match {
+    private def isUndefined(tp: Type): Boolean = tp.dealias match {
       case _: WildcardType => true
-      case defn.FunctionOf(args, result, _) => args.exists(isUndefined) || isUndefined(result)
+      case defn.FunctionNOf(args, result, _) => args.exists(isUndefined) || isUndefined(result)
       case _ => false
     }
 
@@ -412,7 +412,7 @@ object ProtoTypes {
               case ValDef(_, tpt, _) if !tpt.isEmpty => typer.typedType(tpt).typeOpt
               case _ => WildcardType
             }
-            targ = arg.withType(defn.FunctionOf(paramTypes, WildcardType))
+            targ = arg.withType(defn.FunctionNOf(paramTypes, WildcardType))
           case Some(_) if !force =>
             targ = arg.withType(WildcardType)
           case _ =>

compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

@@ -116,7 +116,7 @@ trait QuotesAndSplices {
       for arg <- typedArgs if arg.symbol.is(Mutable) do // TODO support these patterns. Possibly using scala.quoted.util.Var
         report.error("References to `var`s cannot be used in higher-order pattern", arg.srcPos)
       val argTypes = typedArgs.map(_.tpe.widenTermRefExpr)
-      val patType = if tree.args.isEmpty then pt else defn.FunctionOf(argTypes, pt)
+      val patType = if tree.args.isEmpty then pt else defn.FunctionNOf(argTypes, pt)
       val pat = typedPattern(tree.body, defn.QuotedExprClass.typeRef.appliedTo(patType))(
         using spliceContext.retractMode(Mode.QuotedPattern).addMode(Mode.Pattern).withOwner(patternOuterContext(ctx).owner))
       val baseType = pat.tpe.baseType(defn.QuotedExprClass)
@@ -143,7 +143,7 @@ trait QuotesAndSplices {
     if isInBraces then // ${x}(...) match an application
       val typedArgs = args.map(arg => typedExpr(arg))
       val argTypes = typedArgs.map(_.tpe.widenTermRefExpr)
-      val splice1 = typedSplicePattern(splice, defn.FunctionOf(argTypes, pt))
+      val splice1 = typedSplicePattern(splice, defn.FunctionNOf(argTypes, pt))
       untpd.cpy.Apply(tree)(splice1.select(nme.apply), typedArgs).withType(pt)
     else // $x(...) higher-order quasipattern
       if args.isEmpty then

compiler/src/dotty/tools/dotc/typer/Synthesizer.scala

@@ -102,7 +102,7 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
       case AppliedType(_, funArgs @ fun :: tupled :: Nil) =>
         def functionTypeEqual(baseFun: Type, actualArgs: List[Type],
             actualRet: Type, expected: Type) =
-          expected =:= defn.FunctionOf(actualArgs, actualRet,
+          expected =:= defn.FunctionNOf(actualArgs, actualRet,
             defn.isContextFunctionType(baseFun))
         val arity: Int =
           if fun.derivesFrom(defn.ErasedFunctionClass) then -1 // TODO support?