Fix compound assignment on arbitrary expression in LHS

(with a convention compound assignment operator defined).

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/AssignmentGenerator.kt

@@ -127,7 +127,7 @@ class AssignmentGenerator(statementGenerator: StatementGenerator) : StatementGen
             is VariableDescriptor ->
                 VariableLValue(ktLeft.startOffset, ktLeft.endOffset, descriptor, operator)
             else ->
-                TODO("Other cases of LHS")
+                OnceExpressionValue(statementGenerator.generateExpression(ktLeft))
         }
     }
 

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/intermediate/OnceExpressionValue.kt

@@ -21,7 +21,7 @@ import org.jetbrains.kotlin.ir.util.render
 import org.jetbrains.kotlin.psi2ir.generators.CallGenerator
 import org.jetbrains.kotlin.types.KotlinType
 
-class OnceExpressionValue(val irExpression: IrExpression) : IntermediateValue {
+class OnceExpressionValue(val irExpression: IrExpression) : LValue, AssignmentReceiver {
     private var instantiated = false
 
     override fun load(): IrExpression {
@@ -31,4 +31,11 @@ class OnceExpressionValue(val irExpression: IrExpression) : IntermediateValue {
     }
 
     override val type: KotlinType get() = irExpression.type
+
+    override fun store(irExpression: IrExpression): IrExpression {
+        throw AssertionError("Expression value ${irExpression.render()} can't be used in store operation")
+    }
+
+    override fun assign(withLValue: (LValue) -> IrExpression): IrExpression =
+            withLValue(this)
 }

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/intermediate/VariableLValue.kt

@@ -40,8 +40,7 @@ class VariableLValue(
             IrGetVariableImpl(startOffset, endOffset, descriptor, irOperator)
 
     override fun store(irExpression: IrExpression): IrExpression =
-            IrSetVariableImpl(startOffset, endOffset, descriptor,
-                                                                  irExpression, irOperator)
+            IrSetVariableImpl(startOffset, endOffset, descriptor, irExpression, irOperator)
 
     override fun assign(withLValue: (LValue) -> IrExpression): IrExpression =
             withLValue(this)