Skip to content

fix: error if {:else} is followed by another {:else} or {:else if ...} - #18900

Merged
dummdidumm merged 1 commit into
sveltejs:mainfrom
maksim-romanov:fix/duplicate-else-clause
Oct 6, 2026
Merged

fix: error if {:else} is followed by another {:else} or {:else if ...}#18900
dummdidumm merged 1 commit into
sveltejs:mainfrom
maksim-romanov:fix/duplicate-else-clause

Conversation

@maksim-romanov

@maksim-romanov maksim-romanov commented Oct 1, 2026 •
edited
Loading

Copy link
Copy Markdown
Contributor

Fixes #18202

When an if block had another else clause after {:else}, either a second {:else} or an {:else if}, the parser just replaced the alternate and the earlier branch vanished from the AST and the compiled output without any error:

{#if a}
	A
{:else}
	B
{:else if b}
	C
{/if}

Prettier then formatted the file and deleted that code. Same thing with two {:else} in an each block. Svelte 4 rejected all of these.

This now throws block_duplicate_clause, same as we already do for duplicate then and catch, including in loose mode. Only templates that were already silently losing a branch start erroring, valid code is not affected. For the {:else} then {:else if} case I kept {:else} in the message, happy to add a dedicated one if you prefer.

Before submitting the PR, please make sure you do the following

  • It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
  • Prefix your PR title with feat:, fix:, chore:, or docs:.
  • This message body should clearly illustrate what problems it solves.
  • Ideally, include a test that fails without this PR but passes with it.
  • If this PR changes code within packages/svelte/src, add a changeset (npx changeset).

Tests and linting

  • Run the tests with pnpm test and lint the project with pnpm lint

@maksim-romanov
fix: error if {:else} is followed by another {:else} or `{:else i…
241ffe0 
…f ...}`

A second else clause after {:else} used to replace the alternate (or each
fallback) and silently drop the earlier branch. Throw block_duplicate_clause
like we already do for duplicate then and catch.

Fixes sveltejs#18202
@pkg-svelte-dev

pkg-svelte-dev Bot commented Oct 1, 2026

Copy link
Copy Markdown

Install the latest version of svelte from 241ffe0:

pnpm add https://pkg.svelte.dev/svelte/c/241ffe05473441bbd2c9c19a2db54a0c42ee46ef

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/svelte/pr/18900

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

@changeset-bot

changeset-bot Bot commented Oct 1, 2026

Copy link
Copy Markdown

🦋 Changeset detected

Latest commit: 241ffe0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package
Name Type
svelte Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

dummdidumm
dummdidumm approved these changes Oct 6, 2026
View reviewed changes

@dummdidumm dummdidumm left a comment

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

thank you!

@dummdidumm
dummdidumm merged commit fe4fb46 into sveltejs:main Oct 6, 2026
12 of 13 checks passed
@github-actions github-actions Bot mentioned this pull request Oct 6, 2026
Merged
dummdidumm pushed a commit that referenced this pull request Oct 6, 2026
@github-actions
Version Packages (#18858)
10fdca7 
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@5.57.2

### Patch Changes

- fix: don't create async deriveds for a component destroyed while
waiting for its top-level `await`
([#18931](#18931))

- fix: prevent untracked derived reads from retaining disconnected
dependencies ([#18829](#18829))

- fix: error if `{:else}` is followed by another `{:else}` or `{:else if
...}` ([#18900](#18900))

- fix: avoid tracking SvelteURLSearchParams during URL updates
([#18791](#18791))

- fix: restore hydration state when custom element attribute updates
throw ([#18467](#18467))

- fix: attach event handlers that are assigned after a top-level `await`
in production ([#18933](#18933))

- fix: flush anything pending before invoking flushSync callback
function ([#18878](#18878))

- fix: preserve location information for `await` wrappers
([#18859](#18859))

- fix: keep a reactive assignment with no dependencies when `migrate`
cannot turn it into a declaration
([#18817](#18817))

- fix: don't hang `migrate` on a declaration that shares a line with its
script tag ([#18816](#18816))

- fix: prevent duplicate subscriptions when reconnecting deriveds
([#18899](#18899))

- fix: recover when an unexpected node replaces a nested boundary
comment during hydration
([#18925](#18925))

- fix: print `{#await}` blocks that only have a pending branch
([#18908](#18908))

- fix: don't warn about a redundant `link` role on `<area>` elements
without an `href`
([#18872](#18872))

- fix: don't throw `state_unsafe_mutation` when the focused element is
removed while `bind:activeElement` is used
([#18921](#18921))

- fix: don't overwrite an unchanged spread `value`, preserving
incomplete number input
([#18864](#18864))

- fix: read batch-local array on each-block commit
([#18879](#18879))

- fix: error at compile time when a declaration in a snippet redeclares
one of its parameters
([#18842](#18842))

- fix: error when using `let:` directives on a component with a
`children` snippet
([#18873](#18873))

- fix: ignore stale boundary reset callbacks
([#18886](#18886))

- fix: handle deferred transitions aborted before initialization
([#18776](#18776))

- fix: prevent hydration mismatch recovery from being intercepted by
error boundaries
([#18841](#18841))

- fix: preserve dynamic element connections during hydration
([#18855](#18855))

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
@github-actions github-actions Bot mentioned this pull request Oct 7, 2026
Open
dadezzz pushed a commit to dadezzz/events-cash-register that referenced this pull request Oct 10, 2026
Renovate [bot] Forgejo
fix(deps): update dependency svelte to v5.57.2 (#332)
e83b14f 
This PR contains the following updates:

| Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) |
|---|---|---|---|
| [svelte](https://svelte.dev) ([source](https://github.com/sveltejs/svelte/tree/HEAD/packages/svelte)) | [`5.57.1` → `5.57.2`](https://renovatebot.com/diffs/npm/svelte/5.57.1/5.57.2) | ![age](https://developer.mend.io/api/mc/badges/age/npm/svelte/5.57.2?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/svelte/5.57.1/5.57.2?slim=true) |

---

### Release Notes

<details>
<summary>sveltejs/svelte (svelte)</summary>

### [`v5.57.2`](https://github.com/sveltejs/svelte/blob/HEAD/packages/svelte/CHANGELOG.md#5572)

[Compare Source](https://github.com/sveltejs/svelte/compare/svelte@5.57.1...svelte@5.57.2)

##### Patch Changes

- fix: don't create async deriveds for a component destroyed while waiting for its top-level `await` ([#&#8203;18931](sveltejs/svelte#18931))

- fix: prevent untracked derived reads from retaining disconnected dependencies ([#&#8203;18829](sveltejs/svelte#18829))

- fix: error if `{:else}` is followed by another `{:else}` or `{:else if ...}` ([#&#8203;18900](sveltejs/svelte#18900))

- fix: avoid tracking SvelteURLSearchParams during URL updates ([#&#8203;18791](sveltejs/svelte#18791))

- fix: restore hydration state when custom element attribute updates throw ([#&#8203;18467](sveltejs/svelte#18467))

- fix: attach event handlers that are assigned after a top-level `await` in production ([#&#8203;18933](sveltejs/svelte#18933))

- fix: flush anything pending before invoking flushSync callback function ([#&#8203;18878](sveltejs/svelte#18878))

- fix: preserve location information for `await` wrappers ([#&#8203;18859](sveltejs/svelte#18859))

- fix: keep a reactive assignment with no dependencies when `migrate` cannot turn it into a declaration ([#&#8203;18817](sveltejs/svelte#18817))

- fix: don't hang `migrate` on a declaration that shares a line with its script tag ([#&#8203;18816](sveltejs/svelte#18816))

- fix: prevent duplicate subscriptions when reconnecting deriveds ([#&#8203;18899](sveltejs/svelte#18899))

- fix: recover when an unexpected node replaces a nested boundary comment during hydration ([#&#8203;18925](sveltejs/svelte#18925))

- fix: print `{#await}` blocks that only have a pending branch ([#&#8203;18908](sveltejs/svelte#18908))

- fix: don't warn about a redundant `link` role on `<area>` elements without an `href` ([#&#8203;18872](sveltejs/svelte#18872))

- fix: don't throw `state_unsafe_mutation` when the focused element is removed while `bind:activeElement` is used ([#&#8203;18921](sveltejs/svelte#18921))

- fix: don't overwrite an unchanged spread `value`, preserving incomplete number input ([#&#8203;18864](sveltejs/svelte#18864))

- fix: read batch-local array on each-block commit ([#&#8203;18879](sveltejs/svelte#18879))

- fix: error at compile time when a declaration in a snippet redeclares one of its parameters ([#&#8203;18842](sveltejs/svelte#18842))

- fix: error when using `let:` directives on a component with a `children` snippet ([#&#8203;18873](sveltejs/svelte#18873))

- fix: ignore stale boundary reset callbacks ([#&#8203;18886](sveltejs/svelte#18886))

- fix: handle deferred transitions aborted before initialization ([#&#8203;18776](sveltejs/svelte#18776))

- fix: prevent hydration mismatch recovery from being intercepted by error boundaries ([#&#8203;18841](sveltejs/svelte#18841))

- fix: preserve dynamic element connections during hydration ([#&#8203;18855](sveltejs/svelte#18855))

</details>

---

### Configuration

📅 **Schedule**: (UTC)

- Branch creation
  - At any time (no schedule defined)
- Automerge
  - At any time (no schedule defined)

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Mend Renovate CLI](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0NC4xNDguNCIsInVwZGF0ZWRJblZlciI6IjQ0LjE0OC40IiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6W119-->
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

@dummdidumm dummdidumm dummdidumm approved these changes

Assignees

No one assigned

Labels

None yet

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

Code sections removed when formatting file with syntax errors

2 participants

@maksim-romanov @dummdidumm