Optimize tail recursion on effectively final methods even when final keyword is absent

src/reflect/scala/reflect/internal/Symbols.scala

@@ -1025,12 +1025,13 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     )
     /** Is this symbol effectively final or a concrete term member of sealed class whose children do not override it */
     final def isEffectivelyFinalOrNotOverridden: Boolean = {
-      def isNotOverridden =
-        owner.isClass && (
-             owner.isEffectivelyFinal
-          || owner.isSealed && owner.sealedChildren.forall(c => c.isEffectivelyFinal && overridingSymbol(c) == NoSymbol)
-        )
-      isEffectivelyFinal || isTerm && !isDeferred && isNotOverridden
+      def isNotOverriddenAt(c: Symbol, hasLocalOwner: Boolean): Boolean = {
+        def checkOverrideIn(sc: Symbol) = overridingSymbol(sc) == NoSymbol && isNotOverriddenAt(sc, hasLocalOwner || sc.originalOwner.isTerm)
+        c.isClass && (c.isEffectivelyFinal || {
+          (c.isSealed || hasLocalOwner) && c.children.forall(checkOverrideIn)
+        })
+      }
+      isEffectivelyFinal || isTerm && !isDeferred && isNotOverriddenAt(owner, owner.originalOwner.isTerm)
     }
 
     /** Is this symbol owned by a package? */

test/files/neg/t9414.check

@@ -0,0 +1,10 @@
+t9414.scala:6: error: could not optimize @tailrec annotated method bar: it is neither private nor final so can be overridden
+      @tailrec def bar: Int = {
+                   ^
+t9414.scala:20: error: could not optimize @tailrec annotated method bar: it is neither private nor final so can be overridden
+      @tailrec def bar: Int = {
+                   ^
+t9414.scala:34: error: could not optimize @tailrec annotated method bar: it is neither private nor final so can be overridden
+    @tailrec def bar: Int = {
+                 ^
+3 errors

test/files/neg/t9414.scala

@@ -0,0 +1,42 @@
+import annotation._
+
+class C {
+  def foo = {
+    class Parent {
+      @tailrec def bar: Int = {
+        println("here we go again")
+        bar
+      }
+    }
+    class Child extends Parent {
+      override def bar = 42
+    }
+  }
+}
+
+class D {
+  def foo = {
+    class Parent {
+      @tailrec def bar: Int = {
+        println("here we go again")
+        bar
+      }
+    }
+    class Child extends Parent
+    class GrandChild extends Child {
+      override def bar = 42
+    }
+  }
+}
+
+object E {
+  sealed class Parent {
+    @tailrec def bar: Int = {
+      println("here we go again")
+      bar
+    }
+  }
+  final class Child extends Parent {
+    override def bar = 42
+  }
+}

test/files/pos/t9414.scala

@@ -0,0 +1,78 @@
+import annotation._
+
+class C {
+  def foo = {
+    class Parent {
+      @tailrec def bar: Int = {
+        println("here we go again")
+        bar
+      }
+    }
+    class Child extends Parent {
+      def notBar = 42
+    }
+  }
+}
+
+class D {
+  def foo = {
+    class Parent {
+      @tailrec def bar: Int = {
+        println("here we go again")
+        bar
+      }
+    }
+    class Child extends Parent
+    class GrandChild extends Child {
+      def notBar = 42
+    }
+  }
+}
+
+object E {
+  sealed class Parent {
+    @tailrec def bar: Int = {
+      println("here we go again")
+      bar
+    }
+  }
+  final class Child extends Parent {
+    def notBar = 42
+  }
+}
+
+class F {
+  def foo = {
+    class Parent {
+      @tailrec def bar: Int = {
+        println("here we go again")
+        bar
+      }
+    }
+    class K {
+      class Child extends Parent {
+        def notBar = 42
+      }
+      class GrandChild extends Child {
+        def neitherBar = 42
+      }
+    }
+  }
+}
+
+class G {
+  sealed class Parent {
+    @tailrec def bar: Int = {
+      println("here we go again")
+      bar
+    }
+  }
+  def foo = {
+    class Child extends Parent {
+      def notBar = 42
+    }
+    class GrandChild extends Child {
+      def neitherBar = 42
+    }
+  }
+}