Fix scala#8276: Do not infer types of default argument getters

Author: nicolasstucki

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

@@ -263,7 +263,7 @@ object desugar {
             name = DefaultGetterName(methName, n),
             tparams = meth.tparams.map(tparam => dropContextBounds(toDefParam(tparam, keepAnnotations = true))),
             vparamss = takeUpTo(normalizedVparamss.nestedMap(toDefParam(_, keepAnnotations = true, keepDefault = false)), n),
-            tpt = TypeTree(),
+            tpt = vparam.tpt,
             rhs = vparam.rhs
           )
           .withMods(Modifiers(mods.flags & (AccessFlags | Synthetic), mods.privateWithin))

tests/neg/i4659b.scala

@@ -0,0 +1,10 @@
+// Tests variance checking on default methods
+import reflect.ClassTag
+
+class Foo[+A: ClassTag](x: A) {
+
+  private[this] val elems: Array[A] = Array(x)
+
+  def f[B](x: Array[B] = elems): Array[B] = x // error: Found: (Foo.this.elems : Array[A])  Required: Array[B]
+
+}

tests/neg/variances-b.scala

@@ -5,7 +5,7 @@ class Foo[+A: ClassTag](x: A) {
 
   private[this] val elems: Array[A] = Array(x)
 
-  def f[B](x: Array[B] = elems): Array[B] = x // error (1) should give a variance error here or ...
+  def f[B](x: Array[B] = ???): Array[B] = x
 
 }
 

tests/neg/variances.scala

@@ -0,0 +1,7 @@
+object NOTHING
+
+inline given [A] as Conversion[NOTHING.type, Option[A]] = _ => None
+
+def apply[A](p: Vector[A], o: Option[A] = NOTHING): Unit = ???
+
+apply[String](Vector.empty)

tests/pos/i8276.scala

@@ -1,8 +1,9 @@
-case class SourcePosition(outer: SourcePosition = (NoSourcePosition: SourcePosition))
+case class SourcePosition(outer: SourcePosition = NoSourcePosition) {
+  // TODO: outer is null because it was not initialized in the consturctor of NoSourcePosition
+  // This is a task for the initalization checker
+  // assert(outer != null)
+}
 
-// The code should not compile -- currently out of reach
 object NoSourcePosition extends SourcePosition()
 
-object Test extends App {
-  assert(NoSourcePosition.outer == null)
-}
+@main def Test = NoSourcePosition