Remove unnecessary type from UnApply

This type is never used, it is just a placeholder to make the tree typed.
It is the `Typed` tree around the `UnApply` that holds the type information.

Author: nicolasstucki

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

@@ -197,9 +197,9 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   def Alternative(trees: List[Tree])(using Context): Alternative =
     ta.assignType(untpd.Alternative(trees), trees)
 
-  def UnApply(fun: Tree, implicits: List[Tree], patterns: List[Tree], proto: Type)(using Context): UnApply = {
+  def UnApply(fun: Tree, implicits: List[Tree], patterns: List[Tree])(using Context): UnApply = {
     assert(fun.isInstanceOf[RefTree] || fun.isInstanceOf[GenericApply])
-    ta.assignType(untpd.UnApply(fun, implicits, patterns), proto)
+    ta.assignType(untpd.UnApply(fun, implicits, patterns), defn.NothingType)
   }
 
   def ValDef(sym: TermSymbol, rhs: LazyTree = EmptyTree)(using Context): ValDef =

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -538,7 +538,8 @@ class TreePickler(pickler: TastyPickler) {
               writeByte(IMPLICITarg)
               pickleTree(implicitArg)
             }
-            pickleType(tree.tpe)
+            // TODO write a dummy type that takes less space?
+            pickleType(tree.tpe) // IGNORED // TODO remove when we can break TASTy compat.
             patterns.foreach(pickleTree)
           }
         case tree: ValDef =>

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -1248,9 +1248,9 @@ class TreeUnpickler(reader: TastyReader,
                   readByte()
                   readTerm()
                 }
-              val patType = readType()
+              val patType = readType() // IGNORED // TODO remove when we can break TASTy compat.
               val argPats = until(end)(readTerm())
-              UnApply(fn, implicitArgs, argPats, patType)
+              UnApply(fn, implicitArgs, argPats)
             case REFINEDtpt =>
               val refineCls = symAtAddr.getOrElse(start,
                 newRefinedClassSymbol(coordAt(start))).asClass

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -1175,7 +1175,7 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
       case UNAPPLYtree =>
         val fun = readTreeRef()
         val args = until(end, () => readTreeRef())
-        UnApply(fun, Nil, args, defn.AnyType) // !!! this is wrong in general
+        UnApply(fun, Nil, args)
 
       case ARRAYVALUEtree =>
         val elemtpt = readTreeRef()

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

@@ -469,10 +469,11 @@ trait QuotesAndSplices {
     val matchModule = if tree.quoted.isTerm then defn.QuoteMatching_ExprMatch else defn.QuoteMatching_TypeMatch
     val unapplyFun = qctx.asInstance(defn.QuoteMatchingClass.typeRef).select(matchModule).select(nme.unapply)
 
-    UnApply(
-      fun = unapplyFun.appliedToTypeTrees(typeBindingsTuple :: TypeTree(patType) :: Nil),
-      implicits = quotedPattern :: Nil,
-      patterns = splicePat :: Nil,
-      proto = quoteClass.typeRef.appliedTo(replaceBindings(quoted1.tpe) & quotedPt))
+    Typed(
+      UnApply(
+        fun = unapplyFun.appliedToTypeTrees(typeBindingsTuple :: TypeTree(patType) :: Nil),
+        implicits = quotedPattern :: Nil,
+        patterns = splicePat :: Nil),
+      TypeTree(quoteClass.typeRef.appliedTo(replaceBindings(quoted1.tpe) & quotedPt)))
   }
 }