esrap 2.3.3: server codegen emits invalid JS when `@type` JSDoc on `export let` meets a `$:` declaration

[Ivaneyko]

Correction (edited shortly after filing): the trigger is esrap 2.3.3, not a Svelte version. The original text bisected over Svelte releases, which was confounded — each install resolved a different transitive esrap. Details below.

Describe the bug

With esrap 2.3.3, generate: 'server' emits syntactically invalid JavaScript when a /** @type {...} */ comment sits on an export let prop and the component also has a $: declaration.

The hoisted declaration for the reactive variable now has its declarator wrapped in parentheses, which is not legal after let:

// esrap 2.3.2 — valid
let /** @type {string} */
c;

// esrap 2.3.3 — invalid
let /** @type {string} */ (
c);

V8 rejects it with SyntaxError: Unexpected strict mode reserved word, oxc/rolldown with The keyword 'let' is reserved — since let cannot start a declaration here, it parses as an identifier reference, which is reserved in strict mode/modules.

generate: 'client' is unaffected, so this only surfaces in SSR builds.

Because svelte depends on esrap: ^2.2.9, a fresh npm install resolves 2.3.3 and any project of this shape starts failing to build with no change on its own side. sveltekit-superforms is one concrete path in: its package entry re-exports dist/client/SuperDebug.svelte as the default export, so the component enters the module graph from every import { superForm } from 'sveltekit-superforms' and fails to parse even though it is never rendered.

Reproduction

MinRepro.svelte:

<script>
	/** @type {string} */
	export let a = 'x';
	$: c = a;
</script>

{c}

import fs from 'node:fs';
import { compile } from 'svelte/compiler';

fs.writeFileSync(
	'out.mjs',
	compile(fs.readFileSync('MinRepro.svelte', 'utf8'), {
		generate: 'server',
		filename: 'MinRepro.svelte'
	}).js.code
);
// node --check out.mjs  ->  SyntaxError: Unexpected strict mode reserved word

Both ingredients are required, and the trigger is specifically @type. Removing the $: line, or using /** Docs. */, @param, @deprecated, @typedef, @returns, a non-JSDoc /* … */ block, or // comments, all produce valid output.

Version boundary

Pinning esrap through overrides with svelte held fixed, on a clean node_modules each time:

esrap	result
2.2.10 … 2.3.2	ok
2.3.3 (latest, published 2026-08-13)	broken

Independent of the Svelte version — 5.56.1 and 5.56.9 are both ok on esrap 2.3.2 and both broken on 2.3.3.

This may belong in sveltejs/esrap rather than here; filing where it surfaces.

Stack

svelte:                     5.56.9 (also reproduced on 5.56.1)
esrap:                      2.3.3  (2.3.2 and earlier are fine)
sveltekit-superforms:       2.30.2
@sveltejs/kit:              2.70.2
@sveltejs/vite-plugin-svelte: 7.3.0
vite:                       8.2.1 (rolldown 1.2.4)
typescript:                 6.0.2
node:                       22.18.0
npm:                        10.9.3
OS:                         macOS 26.5.2

Severity

annoyance — the compiler produces invalid output silently rather than erroring, so it surfaces as a bundler parse error in an unrelated node_modules file.

[kyoshino]

I just encountered the same issue after updating to svelte@5.56.9.

$ vitest run

 RUN  v4.1.10 /Users/Kohei/Sites/sveltia-i18n

 ❯ src/lib/index.test.js (0 test)

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ Failed Suites 1 ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 FAIL  src/lib/index.test.js [ src/lib/index.test.js ]
RolldownError: Parse failure: Parse failed with 1 error:
Expected a semicolon or an implicit semicolon after a statement, but found none
664:   options, /** @type {any} */
665:   operand
666: ) => {
      ^
667:   const mv = fn(ctx, options, operand);
668:   const preset = getMessagePreset(kind);
At file: /src/lib/index.svelte.js:666:1
  File: /src/lib/index.svelte.js:666:1
  664 |         options, /** @type {any} */
  665 |         operand
  666 |  ) => {
      |   ^
  667 |         const mv = fn(ctx, options, operand);
  668 |         const preset = getMessagePreset(kind);
 ❯ error node_modules/.pnpm/rolldown@1.2.4/node_modules/rolldown/dist/shared/logs-DmYCAKcW.mjs:159:24
 ❯ normalizeParseError node_modules/.pnpm/rolldown@1.2.4/node_modules/rolldown/dist/parse-ast-index.mjs:25:9
 ❯ wrap node_modules/.pnpm/rolldown@1.2.4/node_modules/rolldown/dist/parse-ast-index.mjs:5:39
 ❯ parseAstAsync node_modules/.pnpm/rolldown@1.2.4/node_modules/rolldown/dist/parse-ast-index.mjs:54:9
 ❯ ssrTransformScript node_modules/.pnpm/vite@8.2.1_@types+node@26.2.0_yaml@2.9.0/node_modules/vite/dist/node/chunks/node.js:12378:9
 ❯ loadAndTransform node_modules/.pnpm/vite@8.2.1_@types+node@26.2.0_yaml@2.9.0/node_modules/vite/dist/node/chunks/node.js:20653:64

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯[1/1]⎯


 Test Files  1 failed (1)
      Tests  no tests
   Start at  15:00:56
   Duration  274ms (transform 22ms, setup 0ms, import 0ms, tests 0ms, environment 136ms)

[ELIFECYCLE] Test failed. See above for more details.

Workaround

The below is Claude’s analysis:

---

Same root cause, but there's a second manifestation worth folding in: function parameters. The cast parens are emitted for any node with a leading /** @type {...} */ comment, and parameter positions don't allow them either.

Repro with esrap alone (no Svelte, no $:, no hoisting):

import { parse } from 'acorn';
import { print } from 'esrap';
import ts from 'esrap/languages/ts';

const source = `const f = (/** @type {any} */ ctx) => {};\n`;

const comments = [];
const ast = parse(source, {
  ecmaVersion: 'latest',
  sourceType: 'module',
  locations: true,
  onComment: comments,
});

console.log(print(ast, ts({ comments })).code);

Output on 2.3.3:

const f = (/** @type {any} */ (ctx)) => {};

Re-parsing that fails with Parenthesized pattern — (a) is not a valid binding pattern.

Every parameter position I tried is affected:

input	2.3.3 output	valid?
const f = (/** @type {any} */ ctx) => {};	const f = (/** @type {any} */ (ctx)) => {};	❌ Parenthesized pattern
function f(/** @type {any} */ ctx) {}	function f(/** @type {any} */ (ctx)) {}	❌ Unexpected token
const f = (a) => (/** @type {any} */ ctx) => {};	const f = (a) => (/** @type {any} */ (ctx)) => {};	❌ Parenthesized pattern
const f = /** @type {any} */ (window);	unchanged	✅

So the last row is the case the parens are actually for; the rule just needs to not fire when the annotated node is a binding rather than an expression.

Bisect matches yours: 2.3.2 OK, 2.3.3 broken.

Inline /** @type {...} */ parameter annotations are the standard way to type a callback parameter in JSDoc-typed JS (it's what TypeScript documents for this), so this hits plain checkJs projects, not just Svelte ones.

For what it's worth on the Svelte side (#18643): the real-world hit is intermittent because Svelte only forwards comments to esrap for some modules — a small .svelte.js file with the exact same function compiles fine, while the same function in a larger module breaks. That made it look like a much narrower bug than it is; at the esrap level it's unconditional.

[dummdidumm]

should be fixed in the latest version of esrap