From 4656e6895dde764e99c01d9dd86379df2c881c8a Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 21 May 2026 20:26:09 +0200
Subject: [PATCH] fix: make unnecessary commit work less likely (#18263)

While looking at
https://github.com/sveltejs/svelte/issues/18221#issuecomment-4497918414
and trying to understand how the invariant can happen I noticed that we
are not correctly filtering during commit.
- we were not ignoring deriveds
- we were not comparing the correct values (checking `source.v` instead
of the saved value) and not checking if their "is a derived" state
differs

I'm not able to come up with a test where something fails without these
(possibly because it's more about an optimization to do less reruns and
not about correctness) fixes, but they do make sense.
---
 .changeset/tired-socks-brake.md               |  5 +++++
 .../src/internal/client/reactivity/batch.js   | 19 ++++++++++++-------
 2 files changed, 17 insertions(+), 7 deletions(-)
 create mode 100644 .changeset/tired-socks-brake.md

diff --git a/.changeset/tired-socks-brake.md b/.changeset/tired-socks-brake.md
new file mode 100644
index 0000000000..1d302ffa60
--- /dev/null
+++ b/.changeset/tired-socks-brake.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: make unnecessary commit work less likely
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index 2803ffc84c..4952001dd6 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -677,8 +677,10 @@ export class Batch {
 
 			if (!batch.#started) continue;
 
-			// Re-run async/block effects that depend on distinct values changed in both batches
-			var others = [...batch.current.keys()].filter((s) => !this.current.has(s));
+			// Re-run async/block effects that depend on distinct values changed in both batches (ignoring deriveds)
+			var others = [...batch.current.keys()].filter(
+				(s) => !(/** @type {[any, boolean]} */ (batch.current.get(s))[1]) && !this.current.has(s)
+			);
 
 			if (others.length === 0) {
 				if (is_earlier) {
@@ -718,11 +720,14 @@ export class Batch {
 				}
 
 				checked = new Map();
-				var current_unequal = [...batch.current.keys()].filter((c) =>
-					this.current.has(c)
-						? /** @type {[any, boolean]} */ (this.current.get(c))[0] !== c.v
-						: true
-				);
+				var current_unequal = [...batch.current]
+					.filter(([c, v1]) => {
+						const v2 = this.current.get(c);
+						if (!v2) return true;
+						// Either their values are different or one is a derived but not the other
+						return v2[0] !== v1[0] || v2[1] !== v1[1];
+					})
+					.map(([c]) => c);
 
 				if (current_unequal.length > 0) {
 					for (const effect of this.#new_effects) {