Use isAbstractOrParamType more

There were some other occurrences of isAbstractType where it was not clear why
type parameters should be excluded. Use isAbstractOrParamType as the new default.

Author: odersky

compiler/src/dotty/tools/dotc/cc/CaptureOps.scala

@@ -150,7 +150,7 @@ extension (tp: Type)
       case tp @ CapturingType(parent, refs) =>
         val pcs = getBoxed(parent)
         if tp.isBoxed then refs ++ pcs else pcs
-      case tp: TypeRef if tp.symbol.isAbstractType => CaptureSet.empty
+      case tp: TypeRef if tp.symbol.isAbstractOrParamType => CaptureSet.empty
       case tp: TypeProxy => getBoxed(tp.superType)
       case tp: AndType => getBoxed(tp.tp1) ** getBoxed(tp.tp2)
       case tp: OrType => getBoxed(tp.tp1) ++ getBoxed(tp.tp2)

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

@@ -266,7 +266,7 @@ object TypeErasure {
         tp.paramNames, tp.paramNames map (Function.const(TypeBounds.upper(defn.ObjectType))), tp.resultType)
 
     if (defn.isPolymorphicAfterErasure(sym)) eraseParamBounds(sym.info.asInstanceOf[PolyType])
-    else if (sym.isAbstractType) TypeAlias(WildcardType)
+    else if (sym.isAbstractOrParamType) TypeAlias(WildcardType)
     else if sym.is(ConstructorProxy) then NoType
     else if (sym.isConstructor) outer.addParam(sym.owner.asClass, erase(tp)(using preErasureCtx))
     else if (sym.is(Label)) erase.eraseResult(sym.info)(using preErasureCtx)

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

@@ -31,7 +31,7 @@ trait Deriving {
     /** A version of Type#underlyingClassRef that works also for higher-kinded types */
     private def underlyingClassRef(tp: Type): Type = tp match {
       case tp: TypeRef if tp.symbol.isClass => tp
-      case tp: TypeRef if tp.symbol.isAbstractType => NoType
+      case tp: TypeRef if tp.symbol.isAbstractOrParamType => NoType
       case tp: TermRef => NoType
       case tp: TypeProxy => underlyingClassRef(tp.superType)
       case _ => NoType

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

@@ -671,7 +671,7 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
 
     def canManifest(tp: Manifestable, topLevel: Boolean) =
       val sym = tp.typeSymbol
-      !sym.isAbstractType
+      !sym.isAbstractOrParamType
       && hasStableErasure(tp)
       && !(topLevel && defn.isBottomClassAfterErasure(sym))