Specialize types of inline values

Specialize types of ibline values even if a wider type was gven in an inherited definition.
This generalizes a previous scheme for final vals.

Author: odersky

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

@@ -1323,15 +1323,8 @@ class Namer { typer: Typer =>
       def cookedRhsType = deskolemize(dealiasIfUnit(widenRhs(rhsType)))
       def lhsType = fullyDefinedType(cookedRhsType, "right-hand side", mdef.span)
       //if (sym.name.toString == "y") println(i"rhs = $rhsType, cooked = $cookedRhsType")
-      if (inherited.exists) {
-        if (sym.is(Final, butNot = Method)) {
-          val tp = lhsType
-          if (tp.isInstanceOf[ConstantType])
-            tp // keep constant types that fill in for a non-constant (to be revised when inline has landed).
-          else inherited
-        }
-        else inherited
-      }
+      if (inherited.exists)
+        if (isInlineVal) lhsType else inherited
       else {
         if (sym.is(Implicit))
           mdef match {

tests/pos/givenFallback.scala

@@ -0,0 +1,15 @@
+trait TC[T] { def x: Int; def y: Int = 0 }
+
+given [T] as TC[T] {
+  inline val x = 1
+}
+
+given as TC[Int] {
+  inline val x = 2
+  inline override val y = 3
+}
+
+object Test extends App {
+  val z: 2 = the[TC[Int]].x
+  val _: 3 = the[TC[Int]].y
+}