Filter/count erased parameters directly on parameters types

We can filter the erased parameters by looking at the `ErasedParamAnnot`.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -1152,7 +1152,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
 
     def etaExpandCFT(using Context): Tree =
       def expand(target: Tree, tp: Type)(using Context): Tree = tp match
-        case defn.ContextFunctionType(argTypes, resType, _) =>
+        case defn.ContextFunctionType(argTypes, resType) =>
           val anonFun = newAnonFun(
             ctx.owner,
             MethodType.companion(isContextual = true)(argTypes, resType),

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

@@ -1878,14 +1878,13 @@ class Definitions {
    *  types `As`, the result type `B` and a whether the type is an erased context function.
    */
   object ContextFunctionType:
-    def unapply(tp: Type)(using Context): Option[(List[Type], Type, List[Boolean])] =
+    def unapply(tp: Type)(using Context): Option[(List[Type], Type)] =
       asContextFunctionType(tp) match
         case PolyFunctionOf(mt: MethodType) =>
-          Some((mt.paramInfos, mt.resType, mt.erasedParams))
+          Some((mt.paramInfos, mt.resType))
         case tp1 if tp1.exists =>
           val args = tp1.functionArgInfos
-          val erasedParams = List.fill(functionArity(tp1)) { false }
-          Some((args.init, args.last, erasedParams))
+          Some((args.init, args.last))
         case _ => None
 
   /** A whitelist of Scala-2 classes that are known to be pure */

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

@@ -130,8 +130,8 @@ class Bridges(root: ClassSymbol, thisPhase: DenotTransformer)(using Context) {
           ctx.typer.typed(untpd.cpy.Apply(ref)(ref, args), member.info.finalResultType)
         else
           val mtWithoutErasedParams = atPhase(erasurePhase) {
-            val defn.ContextFunctionType(argTypes, resType, erasedParams) = tp.dealias: @unchecked
-            val paramInfos = argTypes.zip(erasedParams).collect { case (argType, erased) if !erased => argType }
+            val defn.ContextFunctionType(argTypes, resType) = tp.dealias: @unchecked
+            val paramInfos = argTypes.filterNot(_.hasAnnotation(defn.ErasedParamAnnot))
             MethodType(paramInfos, resType)
           }
           val anonFun = newAnonFun(ctx.owner, mtWithoutErasedParams, coord = ctx.owner.coord)

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

@@ -20,7 +20,7 @@ object ContextFunctionResults:
    */
   def annotateContextResults(mdef: DefDef)(using Context): Unit =
     def contextResultCount(rhs: Tree, tp: Type): Int = tp match
-      case defn.ContextFunctionType(_, resTpe, _) =>
+      case defn.ContextFunctionType(_, resTpe) =>
         rhs match
           case closureDef(meth) => 1 + contextResultCount(meth.rhs, resTpe)
           case _ => 0
@@ -58,7 +58,8 @@ object ContextFunctionResults:
    */
   def contextResultsAreErased(sym: Symbol)(using Context): Boolean =
     def allErased(tp: Type): Boolean = tp.dealias match
-      case defn.ContextFunctionType(_, resTpe, erasedParams) => !erasedParams.contains(false) && allErased(resTpe)
+      case defn.ContextFunctionType(argTpes, resTpe) =>
+        argTpes.forall(_.hasAnnotation(defn.ErasedParamAnnot)) && allErased(resTpe)
       case _ => true
     contextResultCount(sym) > 0 && allErased(sym.info.finalResultType)
 
@@ -72,7 +73,7 @@ object ContextFunctionResults:
         integrateContextResults(rt, crCount)
       case tp: MethodOrPoly =>
         tp.derivedLambdaType(resType = integrateContextResults(tp.resType, crCount))
-      case defn.ContextFunctionType(argTypes, resType, erasedParams) =>
+      case defn.ContextFunctionType(argTypes, resType) =>
         MethodType(argTypes, integrateContextResults(resType, crCount - 1))
 
   /** The total number of parameters of method `sym`, not counting
@@ -83,10 +84,10 @@ object ContextFunctionResults:
     def contextParamCount(tp: Type, crCount: Int): Int =
       if crCount == 0 then 0
       else
-        val defn.ContextFunctionType(params, resTpe, erasedParams) = tp: @unchecked
+        val defn.ContextFunctionType(params, resTpe) = tp: @unchecked
         val rest = contextParamCount(resTpe, crCount - 1)
-        // TODO use mt.nonErasedParamCount
-        if erasedParams.contains(true) then erasedParams.count(_ == false) + rest else params.length + rest // TODO use mt.nonErasedParamCount
+        val nonErasedParams = params.count(!_.hasAnnotation(defn.ErasedParamAnnot))
+        nonErasedParams + rest
 
     def normalParamCount(tp: Type): Int = tp.widenExpr.stripPoly match
       case mt @ MethodType(pnames) => mt.nonErasedParamCount + normalParamCount(mt.resType)
@@ -100,7 +101,7 @@ object ContextFunctionResults:
     def recur(tp: Type, n: Int): Type =
       if n == 0 then tp
       else tp match
-        case defn.ContextFunctionType(_, resTpe, _) => recur(resTpe, n - 1)
+        case defn.ContextFunctionType(_, resTpe) => recur(resTpe, n - 1)
     recur(meth.info.finalResultType, depth)
 
   /** Should selection `tree` be eliminated since it refers to an `apply`
@@ -115,7 +116,7 @@ object ContextFunctionResults:
       case Select(qual, name) =>
         if name == nme.apply then
           qual.tpe match
-            case defn.ContextFunctionType(_, _, _) =>
+            case defn.ContextFunctionType(_, _) =>
               integrateSelect(qual, n + 1)
             case _ if defn.isContextFunctionClass(tree.symbol.maybeOwner) => // for TermRefs
               integrateSelect(qual, n + 1)

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

@@ -167,7 +167,7 @@ object ErrorReporting {
       val normPt = normalize(pt, pt)
 
       def contextFunctionCount(tp: Type): Int = tp.stripped match
-        case defn.ContextFunctionType(_, restp, _) => 1 + contextFunctionCount(restp)
+        case defn.ContextFunctionType(_, restp) => 1 + contextFunctionCount(restp)
         case _ => 0
       def strippedTpCount = contextFunctionCount(tree.tpe) - contextFunctionCount(normTp)
       def strippedPtCount = contextFunctionCount(pt) - contextFunctionCount(normPt)

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

@@ -1893,7 +1893,7 @@ class Namer { typer: Typer =>
       val originalTp = defaultParamType
       val approxTp = wildApprox(originalTp)
       approxTp.stripPoly match
-        case atp @ defn.ContextFunctionType(_, resType, _)
+        case atp @ defn.ContextFunctionType(_, resType)
         if !defn.isNonRefinedFunction(atp) // in this case `resType` is lying, gives us only the non-dependent upper bound
             || resType.existsPart(_.isInstanceOf[WildcardType], StopAt.Static, forceLazy = false) =>
           originalTp