fix: print a space before the catch binding in {#await ... catch x}

[winklemad]

print() emits unparseable output for the shorthand {#await ... catch x} form. Round-tripping the example straight out of the await docs:

import { parse, print } from 'svelte/compiler';

const src = '{#await promise catch error}\n\t<p>The error is {error}</p>\n{/await}\n';
print(parse(src, { modern: true })).code;
// '{#await promise catcherror}\n\t<p>The error is {error}</p>\n{/await}'

parse(that, { modern: true });
// throws: Expected whitespace

The catch clause gates its trailing space on node.value — the then binding — instead of node.error:

 if (node.catch) {
-    context.write(node.value ? 'catch ' : 'catch');
+    context.write(node.error ? 'catch ' : 'catch');
     if (node.error) context.visit(node.error);

The then clause immediately above is correct (node.value ? 'then ' : 'then', paired with context.visit(node.value)), so this looks like it was copied down without swapping the property.

It also affects the long form whenever {:then} has no binding, since node.value is null there too:

{#await promise}…{:then}…{:catch error}   ->   {:catcherror}

{#await p}{:then v}{:catch e} round-trips today only incidentally, because node.value happens to be truthy.

node.error appears exactly once in the printer, and there are only two space-gating ternaries of this shape — line 692 (then, correct) and this one — so this is the whole class.

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
  • No issue filed — this is a small self-contained bug fix rather than a feature or large change. Happy to open one if you'd prefer it tracked.
• 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.
  • tests/print/samples/await-block-shorthand. On main it fails with expected '{#await promise catcherror}…' to deeply equal '{#await promise catch error}…'. The sample also covers {:catch} and {#await p then v} with no binding, which must keep emitting a bare catch/then — so the fix can't over-correct.
• 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
  • pnpm test: 33 files, 7687 passed, 69 skipped, 0 failed. pnpm lint: eslint clean, prettier clean.

[pkg-svelte-dev]

Install the latest version of svelte from 831ffb3:

pnpm add https://pkg.svelte.dev/svelte/c/831ffb315b90c0d93611308573c728913e64b88b

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/svelte/pr/18645

Note

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

[changeset-bot]

🦋 Changeset detected

Latest commit: 831ffb3

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

This PR includes changesets to release 1 package

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svelte	Patch

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