Unguard GADT selection healing

Author: dwijnand

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

@@ -3994,10 +3994,8 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
             gadts.println(i"Trying to heal member selection by GADT-approximating $wtp")
             val gadtApprox = Inferencing.approximateGADT(wtp)
             gadts.println(i"GADT-approximated $wtp ~~ $gadtApprox")
-            if pt.isMatchedBy(gadtApprox) then
-              gadts.println(i"Member selection healed by GADT approximation")
-              tree.cast(gadtApprox)
-            else tree
+            gadts.println(i"Member selection healed by GADT approximation")
+            tree.cast(gadtApprox)
           else if tree.tpe.derivesFrom(defn.PairClass) && !defn.isTupleNType(tree.tpe.widenDealias) then
             // If this is a generic tuple we need to cast it to make the TupleN/ members accessible.
             // This works only for generic tuples of known size up to 22.

tests/pos/i16603.scala

@@ -0,0 +1,20 @@
+trait MyData
+
+object MyData:
+  extension (m: MyData)
+    def printIt() = println("hey from my data")
+
+class MyClass:
+  def sel(s: String): Int = s.hashCode()
+
+enum MyTag[A]:
+  case MyDataTag  extends MyTag[MyData]
+  case MyClassTag extends MyTag[MyClass]
+
+def callExtension[A](tag: MyTag[A], a:A): Unit =
+  tag match
+    case MyTag.MyDataTag  => a.printIt()
+    case MyTag.MyClassTag => a.sel("hi")
+
+def callExtensionDirectly(m: MyData): Unit =
+  m.printIt()