chore:Update for TS7 #16485

sandersn · 2025-07-23T15:20:39Z

I am testing Typescript 7's JS support, which I've largely rewritten during the switch to Go. That means Javascript code will need to change much more than Typescript code. Fortunately, most of the changes are for the better: Javascript semantics are now nearly identical to Typescript semantics. It's much stricter and no longer has some persistent bugs that arose from shady JS handling I wrote years ago.

This PR changes Svelte so that it compiles both with TS5.* and TS7, which means that occasionally there are duplicative or non-obvious changes. I'll annotate the interesting changes to explain why I made them.

Because TS7 is quite a way off, I don't know whether you'll want to take this PR. Most of the changes are for the better, because they're due to stricter TS-aligned checking. But some are neutral and there is the previously mentioned duplication in a few places.

Temporary note: if you try this with the nightly ts-native vscode extension, it will still be missing one or two bug fixes until today (2025-07-23) or tomorrow (2025-07-24).

I am testing Typescript 7's JS support, which I've largely rewritten during the switch to Go. That means Javascript code will need to change much more than Typescript code. Fortunately, most of the changes are for the better: Javascript semantics are now nearly identical to Typescript semantics. It's much stricter and no longer has some persistent bugs that arose from shady JS handling I wrote years ago. This PR changes Svelte so that it compiles both with TS5.* and TS7, which means that occasionally there are duplicative or non-obvious changes. I'll annotate the interesting changes to explain why I made them. Because TS7 is quite a way off, I don't know whether you'll want to take this PR. Most of the changes are for the better, because they're due to stricter TS-aligned checking. But some are neutral and there is the previously mentioned duplication in a few places.

changeset-bot · 2025-07-23T15:20:44Z

🦋 Changeset detected

Latest commit: c2f5e05

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

github-actions · 2025-07-23T15:35:40Z

Playground

pnpm add https://pkg.pr.new/svelte@16485

sandersn · 2025-07-23T15:24:22Z

packages/svelte/scripts/generate-types.js

@@ -26,7 +26,7 @@ await createBundle({
 		// so that types/properties with `@internal` (and its dependencies) are removed from the output
 		stripInternal: true,
 		paths: Object.fromEntries(
-			Object.entries(pkg.imports).map(([key, value]) => {
+			Object.entries(pkg.imports).map(/** @param {[string,any]} import */([key, value]) => {


pkg.imports: any and Object.entries now infers [string, unknown] instead of [string, any]. This is stricter, and what happens in .ts files, but requires an explicit param type.
This shows up quite a bit in this PR.

sandersn · 2025-07-23T15:25:16Z

packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js

@@ -9,8 +9,8 @@ import {
 import { regex_ends_with_whitespace, regex_starts_with_whitespace } from '../../patterns.js';
 import { get_attribute_chunks, is_text_attribute } from '../../../utils/ast.js';

-/** @typedef {NODE_PROBABLY_EXISTS | NODE_DEFINITELY_EXISTS} NodeExistsValue */
-/** @typedef {FORWARD | BACKWARD} Direction */
+/** @typedef {typeof NODE_PROBABLY_EXISTS | typeof NODE_DEFINITELY_EXISTS} NodeExistsValue */


JS type annotations no longer insert typeof in places where it finds a value but expects a type. You have to do it explicitly, like in TS.

sandersn · 2025-07-23T15:26:56Z

packages/svelte/src/compiler/phases/2-analyze/utils/check_graph_for_cycles.js

@@ -14,6 +14,7 @@ export default function check_graph_for_cycles(edges) {
 	}, new Map());

 	const visited = new Set();
+	/** @type {Set<T>} */


new Set(): Set<unknown> now, not Set<any>, so you have to explicitly provide a type. I think I gave real types throughout this PR rather than Set<any>, so the typing ends up better than before.

sandersn · 2025-07-23T15:28:54Z

packages/svelte/src/compiler/legacy.js

@@ -55,7 +55,7 @@ export function convert(source, ast) {

 				// Insert svelte:options back into the root nodes
 				if (/** @type {any} */ (options)?.__raw__) {
-					let idx = node.fragment.nodes.findIndex((node) => options.end <= node.start);
+					let idx = node.fragment.nodes.findIndex((node) => /** @type {any} */ (options).end <= node.start);


same as before; options would be unknown in TS7 without this cast.

sandersn · 2025-07-23T15:30:40Z

packages/svelte/src/internal/client/dev/hmr.js

@@ -64,7 +64,7 @@ export function hmr(original, get_source) {
 	// @ts-expect-error
 	wrapper[FILENAME] = original[FILENAME];

-	// @ts-expect-error
+	// @ts-ignore


The error being ignored here is bogus, a result of wonky JS checking that mistakenly causes a circularity. In TS7, this bug is fixed. If this were a complete upgrade to TS7, I would remove this line, but since I want it to compile on TS5 and TS7, I switched it to ts-ignore.

sandersn · 2025-07-23T15:42:36Z

packages/svelte/src/index-client.js

@@ -160,10 +160,14 @@ export function createEventDispatcher() {
 		e.lifecycle_outside_component('createEventDispatcher');
 	}

+	/**


same: signature-to-signature checking (like when you're checking that a returned function has the right type) is stricter in TS7, so you have to explicitly note that detail and options are optional.

I also improved the cast on type but I can't remember if that's actually necessary.

sandersn · 2025-07-23T15:43:24Z

packages/svelte/tests/runtime-browser/assert.js

@@ -87,15 +88,15 @@ function normalize_html(window, html) {
 /** @param {any} node */
 function normalize_children(node) {
 	// sort attributes
-	const attributes = Array.from(node.attributes).sort((a, b) => {
+	const attributes = Array.from(node.attributes).sort((/** @type {any} */ a,/** @type {any} */ b) => {


same as above; Array.from(node.attributes) infers unknown[] in TS7.

sandersn · 2025-07-23T15:44:53Z

packages/svelte/tests/animation-helpers.js

@@ -54,14 +56,24 @@ class Animation {

 	/**
 	 * @param {HTMLElement} target
-	 * @param {Keyframe[]} keyframes
-	 * @param {{ duration: number, delay: number }} options
+	 * @param {Keyframe[] | PropertyIndexedKeyframes | null} keyframes


I kind of went overboard here fixing up this test to handle the DOM types. It's probably better to turn a bunch of these types to any instead. I needed to do something because of the improved signature arity checking in TS7.

sandersn · 2025-07-23T15:45:12Z

packages/svelte/tests/animation-helpers.js

@@ -189,13 +201,15 @@ function interpolate(a, b, p) {
 * @param {{duration: number, delay: number}} options
 * @returns {globalThis.Animation}
 */
+// @ts-ignore


the location of the error to be ignored moved in TS7 to match the location reported in a .ts file

sandersn · 2025-07-23T15:45:48Z

packages/svelte/tests/helpers.js

@@ -43,6 +43,7 @@ export function create_deferred() {
 	/** @param {any} [reason] */
 	let reject = (reason) => {};

+	/** @type {Promise<any>} */


TS7 inferred promise: Promise<unknown> without an explicit annotation.

sandersn · 2025-07-23T15:56:45Z

packages/svelte/src/internal/client/reactivity/props.js

-		if (arguments.length > 0) {
-			const new_value = mutation ? get(d) : runes && bindable ? proxy(value) : value;
+	return /** @type {() => V} */ (
+		function (/** @type {any} */ value, /** @type {boolean} */ mutation) {


after running prettier, Hide Whitespace is basically required to review this PR

elliott-with-the-longest-name-on-github

I'm really excited to see TSGo hit the ground -- it's a gargantuan undertaking from you guys. We're glad we can be a bit of a guinea pig for typed JS! Feel free to run sveltejs/kit through its paces as well -- that one has some demons, especially in all of the crazy rootDirs and generated types stuff we do.

elliott-with-the-longest-name-on-github · 2025-07-23T17:28:28Z

packages/svelte/src/internal/client/reactivity/equality.js

@@ -1,9 +1,9 @@
 /** @import { Equals } from '#client' */

 /** @type {Equals} */
-export function equals(value) {
+export const equals = function (value) {


sigh, this is actually one of the few places I liked JSDoc more than TS -- the fact that there's no way to type function declarations in TS grinds my gears!

FWIW this actually is going to negatively impact us -- in our language tools, whenever you export function load from a +page file, we insert /** @type {Load} */ above it to provide you generated types without you having to explicitly import and use them. I'm sure we can find a workaround but it'll at least be somewhat more difficult now, as we can't just change function declarations to const {name} = () => {} as it's semantically different

jakebailey · 2025-07-23T17:36:04Z

especially in all of the crazy rootDirs and generated types stuff we do.

Just to note it, we don't yet do rootDirs because we thought we were going to remove that feature (it's wonky and usually has much better replacements, which IMO you all should consider, for the same reasons paths is usually the wrong tool), but since everyone hit it, we are going to have to implement it anyway.

sandersn added 2 commits July 23, 2025 08:02

add changeset

3de210e

revert scribbles mistakenly added

f8bf282

sandersn commented Jul 23, 2025

View reviewed changes

pnpm run format

84b50a6

sandersn commented Jul 23, 2025

View reviewed changes

revert mistaken edit

c2f5e05

elliott-with-the-longest-name-on-github reviewed Jul 23, 2025

View reviewed changes

jakebailey mentioned this pull request Jul 23, 2025

Accept and document jsdoc diffs, round 1 microsoft/typescript-go#1426

Open

Uh oh!

chore:Update for TS7 #16485

Are you sure you want to change the base?

chore:Update for TS7 #16485

Conversation

sandersn commented Jul 23, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

changeset-bot bot commented Jul 23, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

🦋 Changeset detected

Uh oh!

github-actions bot commented Jul 23, 2025

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

elliott-with-the-longest-name-on-github left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

jakebailey commented Jul 23, 2025

Uh oh!

Uh oh!

Pfad - The Proxy pFad of © 2024 Garber Painting. All rights reserved.

sandersn commented Jul 23, 2025 •

edited

Loading

changeset-bot bot commented Jul 23, 2025 •

edited

Loading