From 8e7319063aa609cca2cbf8cdf1958e5392dd2fa0 Mon Sep 17 00:00:00 2001 From: Simon H <5968653+dummdidumm@users.noreply.github.com> Date: Mon, 20 Apr 2026 16:35:09 +0200 Subject: [PATCH 1/2] fix: don't mark deriveds while an effect is updating (#18124) Fixes #18123 This makes setting state inside effects slightly slower theoretically (since they hit the new guard), but I verified that the original issue for which we introduced this (#16658) is still fast with this change. The more we add logic to this the more I think we should investigate switching to a different mechanism. I tried using a `Set` previously but it did hurt the benchmarks a bit - might try to revisit a variant of this. --------- Co-authored-by: github-actions[bot] --- .changeset/common-candles-sneeze.md | 5 ++++ .../svelte/src/internal/client/constants.js | 3 +- .../src/internal/client/reactivity/sources.js | 10 +++++-- .../Child.svelte | 7 +++++ .../_config.js | 29 +++++++++++++++++++ .../main.svelte | 14 +++++++++ .../store.svelte.js | 13 +++++++++ 7 files changed, 77 insertions(+), 4 deletions(-) create mode 100644 .changeset/common-candles-sneeze.md create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/Child.svelte create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/_config.js create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/main.svelte create mode 100644 packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/store.svelte.js diff --git a/.changeset/common-candles-sneeze.md b/.changeset/common-candles-sneeze.md new file mode 100644 index 0000000000..a0ef7b610b --- /dev/null +++ b/.changeset/common-candles-sneeze.md @@ -0,0 +1,5 @@ +--- +'svelte': patch +--- + +fix: don't mark deriveds while an effect is updating diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js index a3ad988ba1..f92fba73be 100644 --- a/packages/svelte/src/internal/client/constants.js +++ b/packages/svelte/src/internal/client/constants.js @@ -48,7 +48,8 @@ export const EFFECT_OFFSCREEN = 1 << 25; /** * Tells that we marked this derived and its reactions as visited during the "mark as (maybe) dirty"-phase. * Will be lifted during execution of the derived and during checking its dirty state (both are necessary - * because a derived might be checked but not executed). + * because a derived might be checked but not executed). This is a pure performance optimization flag and + * should not be used for any other purpose! */ export const WAS_MARKED = 1 << 16; diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js index 9235c5f673..1831183e6f 100644 --- a/packages/svelte/src/internal/client/reactivity/sources.js +++ b/packages/svelte/src/internal/client/reactivity/sources.js @@ -27,7 +27,8 @@ import { ROOT_EFFECT, ASYNC, WAS_MARKED, - CONNECTED + CONNECTED, + REACTION_IS_UPDATING } from '#client/constants'; import * as e from '../errors.js'; import { legacy_mode_flag, tracing_mode_flag } from '../../flags/index.js'; @@ -356,8 +357,11 @@ function mark_reactions(signal, status, updated_during_traversal) { batch_values?.delete(derived); if ((flags & WAS_MARKED) === 0) { - // Only connected deriveds can be reliably unmarked right away - if (flags & CONNECTED) { + // Only connected deriveds being executed outside the update cycle can be reliably unmarked right away + if ( + flags & CONNECTED && + (active_effect === null || (active_effect.f & REACTION_IS_UPDATING) === 0) + ) { reaction.f |= WAS_MARKED; } diff --git a/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/Child.svelte b/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/Child.svelte new file mode 100644 index 0000000000..9771762c0b --- /dev/null +++ b/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/Child.svelte @@ -0,0 +1,7 @@ + diff --git a/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/_config.js b/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/_config.js new file mode 100644 index 0000000000..60985cdd12 --- /dev/null +++ b/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/_config.js @@ -0,0 +1,29 @@ +import { flushSync } from 'svelte'; +import { test } from '../../test'; + +export default test({ + async test({ assert, target }) { + const [show, hide] = target.querySelectorAll('button'); + + hide.click(); + flushSync(); + assert.htmlEqual( + target.innerHTML, + ` + + + ` + ); + + show.click(); + flushSync(); + assert.htmlEqual( + target.innerHTML, + ` + + +
visible
+ ` + ); + } +}); diff --git a/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/main.svelte b/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/main.svelte new file mode 100644 index 0000000000..3359a6305b --- /dev/null +++ b/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/main.svelte @@ -0,0 +1,14 @@ + + + + +{#if visible2} + +
visible
+{/if} diff --git a/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/store.svelte.js b/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/store.svelte.js new file mode 100644 index 0000000000..b48155e823 --- /dev/null +++ b/packages/svelte/tests/runtime-runes/samples/derived-dep-set-while-rendering/store.svelte.js @@ -0,0 +1,13 @@ +class RawStore { + values = $state.raw({ visible: true }); + + get(key) { + return this.values[key]; + } + + set(key, value) { + this.values = { ...this.values, [key]: value }; + } +} + +export const store = new RawStore(); From b771df346444d486243882099d2a36f88e32dde0 Mon Sep 17 00:00:00 2001 From: "github-actions[bot]" <41898282+github-actions[bot]@users.noreply.github.com> Date: Thu, 23 Apr 2026 17:44:54 -0600 Subject: [PATCH 2/2] Version Packages (#18125) This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## svelte@5.55.5 ### Patch Changes - fix: don't mark deriveds while an effect is updating ([#18124](https://github.com/sveltejs/svelte/pull/18124)) - fix: do not dispatch introstart event with animation of animate directive ([#18122](https://github.com/sveltejs/svelte/pull/18122)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> --- .changeset/common-candles-sneeze.md | 5 ----- .changeset/hip-flowers-give.md | 5 ----- packages/svelte/CHANGELOG.md | 8 ++++++++ packages/svelte/package.json | 2 +- packages/svelte/src/version.js | 2 +- 5 files changed, 10 insertions(+), 12 deletions(-) delete mode 100644 .changeset/common-candles-sneeze.md delete mode 100644 .changeset/hip-flowers-give.md diff --git a/.changeset/common-candles-sneeze.md b/.changeset/common-candles-sneeze.md deleted file mode 100644 index a0ef7b610b..0000000000 --- a/.changeset/common-candles-sneeze.md +++ /dev/null @@ -1,5 +0,0 @@ ---- -'svelte': patch ---- - -fix: don't mark deriveds while an effect is updating diff --git a/.changeset/hip-flowers-give.md b/.changeset/hip-flowers-give.md deleted file mode 100644 index 77f4dd8892..0000000000 --- a/.changeset/hip-flowers-give.md +++ /dev/null @@ -1,5 +0,0 @@ ---- -'svelte': patch ---- - -fix: do not dispatch introstart event with animation of animate directive diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md index 7aa8f9818e..8e0f8a0916 100644 --- a/packages/svelte/CHANGELOG.md +++ b/packages/svelte/CHANGELOG.md @@ -1,5 +1,13 @@ # svelte +## 5.55.5 + +### Patch Changes + +- fix: don't mark deriveds while an effect is updating ([#18124](https://github.com/sveltejs/svelte/pull/18124)) + +- fix: do not dispatch introstart event with animation of animate directive ([#18122](https://github.com/sveltejs/svelte/pull/18122)) + ## 5.55.4 ### Patch Changes diff --git a/packages/svelte/package.json b/packages/svelte/package.json index 12aa895ecf..a4ae208913 100644 --- a/packages/svelte/package.json +++ b/packages/svelte/package.json @@ -2,7 +2,7 @@ "name": "svelte", "description": "Cybernetically enhanced web apps", "license": "MIT", - "version": "5.55.4", + "version": "5.55.5", "type": "module", "types": "./types/index.d.ts", "engines": { diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js index cb8d3f76ab..04b0b0398a 100644 --- a/packages/svelte/src/version.js +++ b/packages/svelte/src/version.js @@ -4,5 +4,5 @@ * The current version, as set in package.json. * @type {string} */ -export const VERSION = '5.55.4'; +export const VERSION = '5.55.5'; export const PUBLIC_VERSION = '5';