Fix #9171: treat _ as _:Any in isMatchTypeShaped

Author: OlivierBlanvillain

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

@@ -1484,6 +1484,11 @@ class Typer extends Namer
                   case defn.MatchCase(patternTp, _) => tpt.tpe frozen_=:= patternTp
                   case _ => false
                 }
+              case (id @ Ident(nme.WILDCARD), pt) =>
+                pt match {
+                  case defn.MatchCase(patternTp, _) => defn.AnyType frozen_=:= patternTp
+                  case _ => false
+                }
               case _ => false
             }
 

tests/pos/unify-wildcard-patterns.scala

@@ -7,7 +7,17 @@ object Test0 {
   def m[X](x: X): M[X] = x match { case _: String => 1  case _: Any => "s" }
 }
 
+object Test1 {
+  type M[X] =            X match { case String => Int   case Any => String }
+  def m[X](x: X): M[X] = x match { case _: String => 1  case _ => "s"      }
+}
+
 object Test2 {
   type M[X] =            X match { case String => Int   case _ => String   }
   def m[X](x: X): M[X] = x match { case _: String => 1  case _: Any => "s" }
 }
+
+object Test3 {
+  type M[X] =            X match { case String => Int   case _ => String   }
+  def m[X](x: X): M[X] = x match { case _: String => 1  case _ => "s"      }
+}