fix: ensure proper HMR updates for dynamic components#18079
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The BranchManager in `branches.js` does create a temporary anchor when creating a new branch offscreen, and deletes it once the branch is committed. Normally this is fine, but the combination of HMR and dynamic components leads to a bug: Since `svelte-component.js` passes the temporary anchor along to the component it generates, which is the HMR wrapper, this wrapper will have an obsolete, disconnected anchor on updates, leading to the content disappearing. The fix is to add a dev-only symbol which we set on the original (then obsolete) anchor to tell about the updated anchor that should be used for HMR updates. Fixes sveltejs/kit#14699 Fixes #17211
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Rich-Harris
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Apr 8, 2026
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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@5.55.3 ### Patch Changes - fix: ensure proper HMR updates for dynamic components ([#18079](#18079)) - fix: correctly calculate `@const` blockers ([#18039](#18039)) - fix: freeze deriveds once their containing effects are destroyed ([#17921](#17921)) - fix: defer error boundary rendering in forks ([#18076](#18076)) - fix: avoid false positives for reactivity loss warning ([#18088](#18088)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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The BranchManager in
branches.jsdoes create a temporary anchor when creating a new branch offscreen, and deletes it once the branch is committed. Normally this is fine, but the combination of HMR and dynamic components leads to a bug: Sincesvelte-component.jspasses the temporary anchor along to the component it generates, which is the HMR wrapper, this wrapper will have an obsolete, disconnected anchor on updates, leading to the content disappearing.The fix is to add a dev-only symbol which we set on the original (then obsolete) anchor to tell about the updated anchor that should be used for HMR updates.
Fixes sveltejs/kit#14699 Fixes #17211