fix: make SvelteSet work with async mode#17902
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…sSupersetOf) and set_like_methods (difference, intersection, symmetricDifference, union) operate on an empty underlying Set instead of the actual data stored in #items. This commit fixes the issue reported at packages/svelte/src/reactivity/set.js:92 **Bug Explanation:** After the refactoring to make SvelteSet async-safe, the data storage changed: - **Before:** Data was stored in the underlying Set via `super.add()` in the constructor - **After:** Data is stored in a reactive `#items` source containing a Set, while `super()` is called without arguments (empty Set) The `#init()` method creates implementations for `read_methods` and `set_like_methods` by delegating to `Set.prototype` methods. However, the code used `set_proto[method].apply(this, v)` where `this` is the SvelteSet instance. Since SvelteSet extends Set but never adds items to itself (all data is in `#items`), calling these Set methods on `this` operates on an empty Set. This caused severe bugs: - `forEach()` would iterate over nothing instead of actual items - `isSubsetOf()` would always return `true` (empty set is subset of everything) - `isSupersetOf()` would always return `false` (empty set can't be superset of non-empty) - `union()` would only return the other set (union with empty set) - `intersection()` would return empty (intersection with empty set) - `difference()` would return empty - `symmetricDifference()` would just return the other set's items **The Fix:** Changed `set_proto[method].apply(this, v)` to `set_proto[method].apply(get(this.#items), v)` in both loops. This ensures the Set methods operate on the actual data stored in `#items` (the reactive Set that contains all the items) rather than the empty underlying Set that the SvelteSet class extends. The fix maintains reactivity since `get(this.#items)` is still called, establishing the reactive dependency as intended. Co-authored-by: Vercel <vercel[bot]@users.noreply.github.com> Co-authored-by: Rich-Harris <hello@rich-harris.dev>
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Follow-up to #17162. It turns out
SvelteSetdidn't work with async mode, because we were mutating the underlying set. To be async-safe, we need to clone it when adding or deleting keys. This does of course add overhead, but I think it's unavoidable (and likely negligible in most cases).I have an alternative PR with a slightly different approach that I'll open in a moment. Both currently have failing tests. Assuming we can get at least one of them to work correctly, this should provide a blueprint for doing the same thing with
SvelteMap.Before submitting the PR, please make sure you do the following
feat:,fix:,chore:, ordocs:.packages/svelte/src, add a changeset (npx changeset).Tests and linting
pnpm testand lint the project withpnpm lint