SI-8330: Mismatch in stack heights

The SI-8233 / 9506d52 missed one case when we need to DROP a null from
a stack: when unboxed Unit is an expected type. If we forgot to do that
in a context where two branches were involved we could end up with
unbalanced stack sizes.

Let's fix that omission and a test covering that specific case to the
original test for SI-8233.

Fixes SI-8330.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/icode/GenICode.scala b/src/compiler/scala/tools/nsc/backend/icode/GenICode.scala
index 81fbbfcabf..1cea4bedda 100644
--- a/src/compiler/scala/tools/nsc/backend/icode/GenICode.scala
+++ b/src/compiler/scala/tools/nsc/backend/icode/GenICode.scala
@@ -1011,9 +1011,10 @@ abstract class GenICode extends SubComponent  {
       // emit conversion
       if (generatedType != expectedType) {
         tree match {
-          case Literal(Constant(null)) if generatedType == NullReference =>
+          case Literal(Constant(null)) if generatedType == NullReference && expectedType != UNIT =>
             // literal null on the stack (as opposed to a boxed null, see SI-8233),
             // we can bypass `adapt` which would otherwise emitt a redundant [DROP, CONSTANT(null)]
+            // except one case: when expected type is UNIT (unboxed) where we need to emit just a DROP
           case _ =>
             adapt(generatedType, expectedType, resCtx, tree.pos)
         }