Fix scala#9166: Harden check for values in patterns based on class inheritance info

Author: liufengyun

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

@@ -3808,10 +3808,19 @@ class Typer extends Namer
               mapOver(tp)
         }
 
-        if tree.symbol.isOneOf(Module | Enum)
-           && !(tree.tpe frozen_<:< pt) // fast track
-           && !(tree.tpe frozen_<:< approx(pt))
-        then
+        val sym = tree.symbol
+
+        // Is it certain that a value of `tree.tpe` never a subtype of `pt`
+        val definiteNotSubType = {
+          val clsA = sym.info.classSymbol
+          val clsB = pt.classSymbol
+          clsA.exists && clsB.exists && !clsA.asClass.mayHaveCommonChild(clsB.asClass)
+          || sym.isOneOf(Module | Enum)
+             && !(tree.tpe frozen_<:< pt) // fast track
+             && !(tree.tpe frozen_<:< approx(pt))
+        }
+
+        if definiteNotSubType then
           // We could check whether `equals` is overriden.
           // Reasons for not doing so:
           // - it complicates the protocol

tests/neg/i9166.scala

@@ -0,0 +1,6 @@
+object UnitTest extends App {
+  def foo(m: Unit) = m match {
+    case runtime.BoxedUnit.UNIT => println("ok") // error
+  }
+  foo(())
+}