fix for KT-237. Unit as value part

idea/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -1970,6 +1970,11 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> {
         if (entries.size() > 22) {
             throw new UnsupportedOperationException("tuple too large");
         }
+        if(entries.size() == 0) {
+            v.visitFieldInsn(Opcodes.GETSTATIC, "jet/Tuple0", "INSTANCE", "Ljet/Tuple0;");
+            return StackValue.onStack(Type.getObjectType("jet/Tuple0"));
+        }
+
         final String className = "jet/Tuple" + entries.size();
         Type tupleType = Type.getObjectType(className);
         StringBuilder signature = new StringBuilder("(");

idea/src/org/jetbrains/jet/codegen/JetTypeMapper.java

@@ -273,14 +273,22 @@ public class JetTypeMapper {
         return owner;
     }
 
+    public Type mapReturnType(@NotNull final JetType jetType, OwnerKind kind) {
+        if (jetType.equals(JetStandardClasses.getUnitType()) || jetType.equals(JetStandardClasses.getNothingType())) {
+            return Type.VOID_TYPE;
+        }
+        return mapType(jetType, kind);
+    }
+
+    public Type mapReturnType(final JetType jetType) {
+        return mapReturnType(jetType, OwnerKind.INTERFACE);
+    }
+
     public Type mapType(final JetType jetType) {
         return mapType(jetType, OwnerKind.INTERFACE);
     }
 
     public Type mapType(@NotNull final JetType jetType, OwnerKind kind) {
-        if (jetType.equals(JetStandardClasses.getUnitType()) || jetType.equals(JetStandardClasses.getNothingType())) {
-            return Type.VOID_TYPE;
-        }
         if (jetType.equals(standardLibrary.getIntType())) {
             return Type.INT_TYPE;
         }
@@ -410,10 +418,10 @@ public class JetTypeMapper {
         if (returnTypeRef == null) {
             final FunctionDescriptor functionDescriptor = bindingContext.get(BindingContext.FUNCTION, f);
             final JetType type = functionDescriptor.getReturnType();
-            returnType = mapType(type);
+            returnType = mapReturnType(type);
         }
         else {
-            returnType = mapType(bindingContext.get(BindingContext.TYPE, returnTypeRef));
+            returnType = mapReturnType(bindingContext.get(BindingContext.TYPE, returnTypeRef));
         }
         return new Method(f.getName(), returnType, parameterTypes.toArray(new Type[parameterTypes.size()]));
     }
@@ -470,7 +478,7 @@ public class JetTypeMapper {
         for (ValueParameterDescriptor parameter : parameters) {
             parameterTypes.add(mapType(parameter.getOutType()));
         }
-        Type returnType = mapType(f.getReturnType());
+        Type returnType = mapReturnType(f.getReturnType());
         return new Method(name, returnType, parameterTypes.toArray(new Type[parameterTypes.size()]));
     }
 

idea/src/org/jetbrains/jet/codegen/StackValue.java

@@ -164,7 +164,7 @@ public abstract class StackValue {
         }
         else if (type.getSort() != Type.VOID && this.type.getSort() == Type.VOID) {
             if(type.getSort() == Type.OBJECT)
-                v.aconst(null);
+                v.visitFieldInsn(Opcodes.GETSTATIC, "jet/Tuple0", "INSTANCE", "Ljet/Tuple0;");
             else if(type == Type.LONG_TYPE)
                 v.lconst(0);
             else if(type == Type.FLOAT_TYPE)

idea/testData/codegen/regressions/kt237.jet

@@ -1,20 +1,41 @@
-fun foreach(array: Array<Int>, action: fun(Int): Unit) {
+fun main(args: Array<String>?) {
+    val y: Unit = () //do not compile
+    A<Unit>()        //do not compile
+    C<Unit>(())      //do not compile
+        //do not compile
+    System.out?.println(fff<Unit>(()))  //do not compile
+    System.out?.println(id<Unit>(y))  //do not compile
+    System.out?.println(fff<Unit>(id<Unit>(y)) == id<Unit>(foreach(Array<Int>(0),{(e : Int) : Unit => })))  //do not compile
+}
+class A<T>()
+
+class C<T>(val value: T) {
+    fun foo(): T = value
+}
+
+fun <T> fff(x: T) : T { return x }
+
+fun <T> id(value: T): T = value
+
+fun foreach(array: Array<Int>?, action: fun(Int): Unit) {
     for (el in array) {
        action(el) //exception through compilation (see below)
     }
 }
-/*
+
 fun almostFilter(array: Array<Int>, action: fun(Int): Int) {
     for (el in array) {
        action(el)
     }
 }
-*/
+
 fun box() : String {
     val a = Array<Int> (3)
     a[0] = 0
     a[1] = 1
     a[2] = 2
     foreach(a, { (el : Int) : Unit => System.out?.println(el) })
+    almostFilter(a, { (el : Int) : Int => el })
+    main(null)
     return "OK"
 }

stdlib/src/jet/Tuple0.java

@@ -0,0 +1,26 @@
+package jet;
+
+/**
+ * @author alex.tkachman
+ */
+public class Tuple0 {
+    public static final Tuple0 INSTANCE = new Tuple0();
+
+    private Tuple0() {
+    }
+
+    @Override
+    public String toString() {
+        return "()";
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        return o == INSTANCE;
+    }
+
+    @Override
+    public int hashCode() {
+        return 239;
+    }
+}