[javanaut][operationExpr][2/2]feat: Add Assignment operation expr wit…

…h xor assignemnt (#342)

* Implement xorAssignmentWith exprs with unit test

src/main/java/com/google/api/generator/engine/ast/AssignmentOperationExpr.java

@@ -95,9 +95,8 @@ private AssignmentOperationExpr build() {
       }
 
       // Check type for XOR and assignment operator (^=).
-      // TODO(summerji): Complete the type-checking for ^= and unit test.
       if (operator.equals(OperatorKind.ASSIGNMENT_XOR)) {
-        Preconditions.checkState(isValidXORAssignmentType(lhsType, rhsType), errorMsg);
+        Preconditions.checkState(isValidXorAssignmentType(lhsType, rhsType), errorMsg);
       }
       return assignmentOperationExpr;
     }
@@ -130,9 +129,25 @@ private boolean isValidMultiplyAssignmentType(TypeNode variableType, TypeNode va
       return false;
     }
 
-    // TODO(summerji): Complete the type-checking for ^= and unit test.
-    private boolean isValidXORAssignmentType(TypeNode variableType, TypeNode valueType) {
-      return true;
+    // isValidXorAssignmentType validates the types for LHS variable expr and RHS expr.
+    // ^= can be applied on boolean and non-floating-point numeric type.
+    private boolean isValidXorAssignmentType(TypeNode variableType, TypeNode valueType) {
+      // LHS is boolean or its boxed type, RHS should be boolean or its boxed type.
+      if (variableType.equals(TypeNode.BOOLEAN)) {
+        return valueType.equals(variableType);
+      }
+      // LHS is integer boxed type, RHS should be non-floating-point numeric types or their boxed
+      // types.
+      if (variableType.equals(TypeNode.INT)) {
+        return TypeNode.isNumericType(valueType) && !TypeNode.isFloatingPointType(valueType);
+      }
+      // LHS is non-floating-point numeric types, RHS should be non-float-point numeric types or
+      // their boxed types.
+      return TypeNode.isNumericType(variableType)
+          && TypeNode.isNumericType(valueType)
+          && !TypeNode.isFloatingPointType(variableType)
+          && !TypeNode.isFloatingPointType(valueType)
+          && !TypeNode.isBoxedType(variableType);
     }
   }
 }