chore: validate promise handling

eslint.config.js

@@ -5,10 +5,19 @@ import lube from 'eslint-plugin-lube';
 export default [
 	...svelte_config,
 	{
+		languageOptions: {
+			parserOptions: {
+				project: true
+			}
+		},
 		plugins: {
 			lube
 		},
 		rules: {
+			'@typescript-eslint/await-thenable': 'error',
+			'@typescript-eslint/no-floating-promises': 'error',
+			'@typescript-eslint/no-misused-promises': 'error',
+			'@typescript-eslint/require-await': 'error',
 			'no-console': 'error',
 			'lube/svelte-naming-convention': ['error', { fixSameNames: true }],
 			// eslint isn't that well-versed with JSDoc to know that `foo: /** @type{..} */ (foo)` isn't a violation of this rule, so turn it off
@@ -43,7 +52,6 @@ export default [
 			'documentation',
 			// contains a fork of the REPL which doesn't adhere to eslint rules
 			'sites/svelte-5-preview/**',
-			'playgrounds/demo/src/**',
 			'tmp/**',
 			// wasn't checked previously, reenable at some point
 			'sites/svelte.dev/**'

packages/svelte/src/internal/client/dom/elements/custom-element.js

@@ -193,13 +193,18 @@ if (typeof HTMLElement === 'function') {
 		disconnectedCallback() {
 			this.$$cn = false;
 			// In a microtask, because this could be a move within the DOM
-			Promise.resolve().then(() => {
-				if (!this.$$cn && this.$$c) {
-					this.$$c.$destroy();
-					destroy_effect(this.$$me);
-					this.$$c = undefined;
-				}
-			});
+			Promise.resolve()
+				.then(() => {
+					if (!this.$$cn && this.$$c) {
+						this.$$c.$destroy();
+						destroy_effect(this.$$me);
+						this.$$c = undefined;
+					}
+				})
+				.catch((err) => {
+					// eslint-disable-next-line no-console
+					console.error(err);
+				});
 		}
 
 		/**

packages/svelte/src/internal/client/dom/elements/misc.js

@@ -42,14 +42,19 @@ export function add_form_reset_listener() {
 			(evt) => {
 				// Needs to happen one tick later or else the dom properties of the form
 				// elements have not updated to their reset values yet
-				Promise.resolve().then(() => {
-					if (!evt.defaultPrevented) {
-						for (const e of /**@type {HTMLFormElement} */ (evt.target).elements) {
-							// @ts-expect-error
-							e.__on_r?.();
+				Promise.resolve()
+					.then(() => {
+						if (!evt.defaultPrevented) {
+							for (const e of /**@type {HTMLFormElement} */ (evt.target).elements) {
+								// @ts-expect-error
+								e.__on_r?.();
+							}
 						}
-					}
-				});
+					})
+					.catch((err) => {
+						// eslint-disable-next-line no-console
+						console.error(err);
+					});
 			},
 			// In the capture phase to guarantee we get noticed of it (no possiblity of stopPropagation)
 			{ capture: true }

packages/svelte/src/internal/client/runtime.js

@@ -635,7 +635,12 @@ export function schedule_effect(signal) {
 	} else if (current_scheduler_mode === FLUSH_YIELD) {
 		if (!is_yield_task_queued) {
 			is_yield_task_queued = true;
-			yield_tick().then(process_deferred);
+			yield_tick()
+				.then(process_deferred)
+				.catch((err) => {
+					// eslint-disable-next-line no-console
+					console.error(err);
+				});
 		}
 	}
 

packages/svelte/src/motion/spring.js

@@ -120,9 +120,14 @@ export function spring(value, opts = {}) {
 			});
 		}
 		return new Promise((fulfil) => {
-			/** @type {import('../internal/client/types').Task} */ (task).promise.then(() => {
-				if (token === current_token) fulfil();
-			});
+			/** @type {import('../internal/client/types').Task} */ (task).promise
+				.then(() => {
+					if (token === current_token) fulfil();
+				})
+				.catch((err) => {
+					// eslint-disable-next-line no-console
+					console.error(err);
+				});
 		});
 	}
 	/** @type {import('./public.js').Spring<T>} */

playgrounds/demo/package.json

@@ -9,9 +9,7 @@
     "ssr": "node ./server.js",
     "build": "vite build --outDir dist/client && vite build --outDir dist/server --ssr src/entry-server.ts",
     "prod": "npm run build && node dist",
-    "preview": "vite preview",
-    "format": "prettier --check --write .",
-    "lint": "prettier --check . && eslint"
+    "preview": "vite preview"
   },
   "devDependencies": {
     "@sveltejs/vite-plugin-svelte": "^3.1.0",

playgrounds/sandbox/run.js

@@ -29,7 +29,9 @@ function mkdirp(dir) {
 const svelte_modules = glob('**/*.svelte', { cwd: `${cwd}/input` });
 const js_modules = glob('**/*.js', { cwd: `${cwd}/input` });
 
-for (const generate of ['client', 'server']) {
+/** @type {Array<'client'|'server'>} */
+const compile_types = ['client', 'server'];
+for (const generate of compile_types) {
 	console.error(`\n--- generating ${generate} ---\n`);
 	for (const file of svelte_modules) {
 		const input = `${cwd}/input/${file}`;

playgrounds/sandbox/tsconfig.json

@@ -13,5 +13,5 @@
 		"allowJs": true,
 		"checkJs": true
 	},
-	"include": ["./input"]
+	"include": ["./run.js", "./input"]
 }