Fix Uncommon Arithmetic Type Errors (#7907)

Author: APickledWalrus

src/main/java/ch/njol/skript/expressions/arithmetic/ArithmeticChain.java

@@ -34,8 +34,7 @@ public class ArithmeticChain<L, R, T> implements ArithmeticGettable<T> {
 	private final ArithmeticGettable<R> right;
 	private final Operator operator;
 	private final Class<? extends T> returnType;
-	@Nullable
-	private OperationInfo<? extends L, ? extends R, ? extends T> operationInfo;
+	private final @Nullable OperationInfo<? extends L, ? extends R, ? extends T> operationInfo;
 
 	public ArithmeticChain(ArithmeticGettable<L> left, Operator operator, ArithmeticGettable<R> right, @Nullable OperationInfo<L, R, T> operationInfo) {
 		this.left = left;
@@ -63,6 +62,7 @@ public T get(Event event) {
 		if (leftClass == Object.class && rightClass == Object.class)
 			return null;
 
+		OperationInfo<? extends L, ? extends R, ? extends T> operationInfo = this.operationInfo;
 		if (left == null && leftClass == Object.class) {
 			operationInfo = lookupOperationInfo(rightClass, OperationInfo::getRight);
 		} else if (right == null && rightClass == Object.class) {

src/test/skript/tests/syntaxes/expressions/ExprArithmetic.sk

@@ -263,3 +263,18 @@ test "arithmetic return types":
 	# however, we can get more specific return types by returning the superclass of the return types of all Object-Number operations
 	set {_location} to location(0,10,0,"world")
 	assert (y-coordinate of {_location} - 4) is 6 with "y-coordinate of {_location} - 4 is not 6 (got '%y-coordinate of {_location} - 4%')"
+
+test "arithmetic type switcheroo":
+	# operation info swap test
+	set {_a} to 1
+	set {_b} to 1
+	loop 2 times:
+		set {_x} to {_a} * {_b}
+		assert {_x} is set with "Failed to get a result"
+		set {_b} to a random vector
+
+	# operation info trick test
+	set {_a} to "Hello"
+	loop 2 times:
+		set {_x} to {_a} + {_b}
+		set {_b} to 5