Another fix for isInaccessibleChildOf

Author: odersky

compiler/src/dotty/tools/dotc/transform/SymUtils.scala

@@ -179,12 +179,14 @@ class SymUtils(val self: Symbol) extends AnyVal {
    *  it cannot be seen from parent class `cls`?
    */
   def isInaccessibleChildOf(cls: Symbol)(given Context): Boolean =
-    def isAccessible(sym: Symbol): Boolean =
-      sym == cls
-      || sym == cls.owner
-      || sym.is(Package)
-      || sym.isType && isAccessible(sym.owner)
-    !isAccessible(self.owner)
+    def isAccessible(sym: Symbol, cls: Symbol): Boolean =
+      if cls.isType && !cls.is(Package) then
+        isAccessible(sym, cls.owner)
+      else
+        sym == cls
+        || sym.is(Package)
+        || sym.isType && isAccessible(sym.owner, cls)
+    !isAccessible(self.owner, cls)
 
   /** If this is a sealed class, its known children in the order of textual occurrence */
   def children(implicit ctx: Context): List[Symbol] = {

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

@@ -2103,17 +2103,19 @@ class Typer extends Namer
         }
 
         val ifpt = defn.asImplicitFunctionType(pt)
-        val result = if (ifpt.exists &&
-            xtree.isTerm &&
-            !untpd.isContextualClosure(xtree) &&
-            !ctx.mode.is(Mode.Pattern) &&
-            !ctx.isAfterTyper &&
-            !ctx.isInlineContext)
-          makeContextualFunction(xtree, ifpt)
-        else xtree match {
-          case xtree: untpd.NameTree => typedNamed(xtree, pt)
-          case xtree => typedUnnamed(xtree)
-        }
+        val result =
+          if ifpt.exists
+             && xtree.isTerm
+             && !untpd.isContextualClosure(xtree)
+             && !ctx.mode.is(Mode.Pattern)
+             && !ctx.isAfterTyper
+             && !ctx.isInlineContext
+          then
+            makeContextualFunction(xtree, ifpt)
+          else xtree match
+            case xtree: untpd.NameTree => typedNamed(xtree, pt)
+            case xtree => typedUnnamed(xtree)
+
         simplify(result, pt, locked)
     }
   }

tests/pos-special/fatal-warnings/patmat-exhaustive.scala

@@ -0,0 +1,10 @@
+def foo: Unit =
+  object O
+    sealed abstract class A
+  class B extends O.A
+  class C extends O.A
+
+  val x: O.A = ???
+  x match
+    case x: B => ???
+    case x: C => ???