chore: simplify deriveds a tiny bit (#12048)

* fix: increment derived versions when updating

* we only need to increment version when setting sources and updating deriveds

* no tests fail if we remove this code

* codegolf

---------

Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>

packages/svelte/src/internal/client/reactivity/deriveds.js

@@ -86,7 +86,7 @@ function destroy_derived_children(signal) {
 /**
  * @param {import('#client').Derived} derived
  * @param {boolean} force_schedule
- * @returns {boolean}
+ * @returns {void}
  */
 export function update_derived(derived, force_schedule) {
 	var previous_updating_derived = updating_derived;
@@ -102,9 +102,7 @@ export function update_derived(derived, force_schedule) {
 
 	set_signal_status(derived, status);
 
-	var is_equal = derived.equals(value);
-
-	if (!is_equal) {
+	if (!derived.equals(value)) {
 		derived.version = increment_version();
 		derived.v = value;
 		mark_reactions(derived, DIRTY, force_schedule);
@@ -113,8 +111,6 @@ export function update_derived(derived, force_schedule) {
 			for (var fn of /** @type {import('#client').DerivedDebug} */ (derived).inspect) fn();
 		}
 	}
-
-	return is_equal;
 }
 
 /**

packages/svelte/src/internal/client/runtime.js

@@ -208,30 +208,28 @@ export function batch_inspect(target, prop, receiver) {
 export function check_dirtiness(reaction) {
 	var flags = reaction.f;
 	var is_dirty = (flags & DIRTY) !== 0;
-	var is_unowned = (flags & UNOWNED) !== 0;
 
-	// If we are unowned, we still need to ensure that we update our version to that
-	// of our dependencies.
-	if (is_dirty && !is_unowned) {
+	if (is_dirty) {
 		return true;
 	}
 
+	var is_unowned = (flags & UNOWNED) !== 0;
 	var is_disconnected = (flags & DISCONNECTED) !== 0;
 
-	if ((flags & MAYBE_DIRTY) !== 0 || (is_dirty && is_unowned)) {
+	if ((flags & MAYBE_DIRTY) !== 0) {
 		var dependencies = reaction.deps;
 
 		if (dependencies !== null) {
 			var length = dependencies.length;
-			var is_equal;
 			var reactions;
 
 			for (var i = 0; i < length; i++) {
 				var dependency = dependencies[i];
 
 				if (!is_dirty && check_dirtiness(/** @type {import('#client').Derived} */ (dependency))) {
-					is_equal = update_derived(/** @type {import('#client').Derived} **/ (dependency), true);
+					update_derived(/** @type {import('#client').Derived} **/ (dependency), true);
 				}
+
 				var version = dependency.version;
 
 				if (is_unowned) {
@@ -239,21 +237,15 @@ export function check_dirtiness(reaction) {
 					// if our dependency write version is higher. If it is then we can assume
 					// that state has changed to a newer version and thus this unowned signal
 					// is also dirty.
-
 					if (version > /** @type {import('#client').Derived} */ (reaction).version) {
-						return !is_equal;
+						return true;
 					}
 
 					if (!current_skip_reaction && !dependency?.reactions?.includes(reaction)) {
 						// If we are working with an unowned signal as part of an effect (due to !current_skip_reaction)
 						// and the version hasn't changed, we still need to check that this reaction
 						// if linked to the dependency source – otherwise future updates will not be caught.
-						reactions = dependency.reactions;
-						if (reactions === null) {
-							dependency.reactions = [reaction];
-						} else {
-							reactions.push(reaction);
-						}
+						(dependency.reactions ??= []).push(reaction);
 					}
 				} else if ((reaction.f & DIRTY) !== 0) {
 					// `signal` might now be dirty, as a result of calling `check_dirtiness` and/or `update_derived`