Add NaN protections for springs

docs/api-reference/general/errors.md

@@ -598,6 +598,50 @@ object should be destroyed.
 
 <div class="fusiondoc-error-api-section" markdown>
 
+## springNanGoal
+
+```
+A spring was given a NaN goal, so some simulation has been skipped. Ensure no
+springs have NaN goals.
+```
+
+**Thrown by:**
+[`Spring`](../../animation/members/spring)
+
+The goal parameter given to the spring during construction contained one or more
+NaN values. 
+
+This typically occurs when zero is accidentally divided by zero, or some other
+invalid mathematical operation has occurred. Check that your code is free of
+maths errors, and handles all edge cases.
+</div>
+
+-----
+
+<div class="fusiondoc-error-api-section" markdown>
+
+## springNanMotion
+
+```
+A spring encountered NaN during motion, so has snapped to the goal position.
+Ensure no springs have NaN positions or velocities.
+```
+
+**Thrown by:**
+[`Spring`](../../animation/members/spring)
+
+While calculating updated position and velocity, one or both of those values
+ended up as NaN.
+
+This typically occurs when zero is accidentally divided by zero, or some other
+invalid mathematical operation has occurred. Check that your code is free of
+maths errors, and handles all edge cases.
+</div>
+
+-----
+
+<div class="fusiondoc-error-api-section" markdown>
+
 ## springTypeMismatch
 
 ```

src/Animation/SpringScheduler.luau

@@ -13,6 +13,7 @@ local External = require(Package.External)
 local packType = require(Package.Animation.packType)
 local springCoefficients = require(Package.Animation.springCoefficients)
 local updateAll = require(Package.State.updateAll)
+local logWarn = require(Package.Logging.logWarn)
 
 type Set<T> = {[T]: unknown}
 
@@ -65,11 +66,22 @@ local function updateAllSprings(
 		local isMoving = false
 
 		for index, goal in ipairs(spring._springGoals) do
+			if goal ~= goal then
+				logWarn("springNanGoal")
+				continue
+			end
+
 			local oldDisplacement = startDisplacements[index]
 			local oldVelocity = startVelocities[index]
 			local newDisplacement = oldDisplacement * posPos + oldVelocity * posVel
 			local newVelocity = oldDisplacement * velPos + oldVelocity * velVel
 
+			if newDisplacement ~= newDisplacement or newVelocity ~= newVelocity then
+				logWarn("springNanMotion")
+				newDisplacement = 0
+				newVelocity = 0
+			end
+
 			if math.abs(newDisplacement) > EPSILON or math.abs(newVelocity) > EPSILON then
 				isMoving = true
 			end

src/Logging/messages.luau

@@ -35,11 +35,13 @@ return {
 	possiblyOutlives = "%s could be destroyed before %s; review the order they're created in, and what scopes they belong to. See discussion #292 on GitHub for advice.",
 	propertySetError = "Error setting property: ERROR_MESSAGE",
 	scopeMissing = "To create %s, provide a scope. (e.g. `%s`). See discussion #292 on GitHub for advice.",
+	springNanGoal = "A spring was given a NaN goal, so some simulation has been skipped. Ensure no springs have NaN goals.",
+	springNanMotion = "A spring encountered NaN during motion, so has snapped to the goal position. Ensure no springs have NaN positions or velocities.",
 	springTypeMismatch = "The type '%s' doesn't match the spring's type '%s'.",
 	stateGetWasRemoved = "`StateObject:get()` has been replaced by `use()` and `peek()` - see discussion #217 on GitHub.",
 	unknownMessage = "Unknown error: ERROR_MESSAGE",
 	unrecognisedChildType = "'%s' type children aren't accepted by `[Children]`.",
 	unrecognisedPropertyKey = "'%s' keys aren't accepted in property tables.",
 	unrecognisedPropertyStage = "'%s' isn't a valid stage for a special key to be applied at.",
-	useAfterDestroy = "%s is no longer valid - it was destroyed before %s. See discussion #292 on GitHub for advice.",
+	useAfterDestroy = "%s is no longer valid - it was destroyed before %s. See discussion #292 on GitHub for advice."
 }