SD-143 allow super calls to methods defined in indirect super classes

The restriction for super calls to methods defined in indirect super
classes introduced in a980fde was over-restrictive. In particular, it
ruled out a valid code pattern to select a method from a superclass
when an unqualified `super` would resolve to an override defined in a
trait (example in the commit as a test).

1 files changed, 7 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/SuperAccessors.scala b/src/compiler/scala/tools/nsc/typechecker/SuperAccessors.scala
index a38d21fe10..963a9dea02 100644
--- a/src/compiler/scala/tools/nsc/typechecker/SuperAccessors.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/SuperAccessors.scala
@@ -152,11 +152,17 @@ abstract class SuperAccessors extends transform.Transform with transform.TypingT
         // SD-143: a call super[T].m that resolves to A.m cannot be translated to correct bytecode if
         //   - A is a class (not a trait / interface), but not the direct superclass. Invokespecial
         //     would select an overriding method in the direct superclass, rather than A.m.
+        //     We allow this if there are statically no intervening overrides.
         //     https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-6.html#jvms-6.5.invokespecial
         //   - A is a java-defined interface and not listed as direct parent of the class. In this
         //     case, `invokespecial A.m` would be invalid.
+        def hasClassOverride(member: Symbol, subclass: Symbol): Boolean = {
+          if (subclass == ObjectClass || subclass == member.owner) false
+          else if (member.overridingSymbol(subclass) != NoSymbol) true
+          else hasClassOverride(member, subclass.superClass)
+        }
         val owner = sym.owner
-        if (!owner.isTrait && owner != clazz.superClass) {
+        if (!owner.isTrait && owner != clazz.superClass && hasClassOverride(sym, clazz.superClass)) {
           reporter.error(sel.pos,
             s"cannot emit super call: the selected $sym is declared in $owner, which is not the direct superclass of $clazz.\n" +
             s"An unqualified super call (super.${sym.name}) would be allowed.")