[NF] Fix Expression.typeOf for size(x).

Belonging to [master]:
  - #3033

Compiler/NFFrontEnd/NFExpression.mo

@@ -784,7 +784,7 @@ public
       case RECORD()          then exp.ty;
       case CALL()            then Call.typeOf(exp.call);
       case SIZE()            then if isSome(exp.dimIndex) then
-                                    Type.INTEGER() else typeOf(exp.exp);
+                                    Type.INTEGER() else Type.sizeType(typeOf(exp.exp));
       case END()             then Type.INTEGER();
       case BINARY()          then Operator.typeOf(exp.operator);
       case UNARY()           then Operator.typeOf(exp.operator);

Compiler/NFFrontEnd/NFType.mo

@@ -892,5 +892,18 @@ public
     end match;
   end isBoxed;
 
+  function sizeType
+    input Type arrayTy;
+    output Type sizeTy;
+  algorithm
+    if Type.isUnknown(arrayTy) then
+      // Return unknown type if the type is unknown, to avoid returning Array[0]
+      // for untyped expressions.
+      sizeTy := Type.UNKNOWN();
+    else
+      sizeTy := Type.ARRAY(Type.INTEGER(), {Dimension.fromInteger(dimensionCount(arrayTy))});
+    end if;
+  end sizeType;
+
   annotation(__OpenModelica_Interface="frontend");
 end NFType;

Compiler/NFFrontEnd/NFTyping.mo

@@ -1892,7 +1892,7 @@ algorithm
           fail();
         end if;
 
-        sizeType := Type.ARRAY(Type.INTEGER(), {Dimension.fromInteger(Type.dimensionCount(exp_ty))});
+        sizeType := Type.sizeType(exp_ty);
       then
         (Expression.SIZE(exp, NONE()), sizeType, Variability.PARAMETER);