tests

CHANGELOG.md

@@ -5,6 +5,7 @@
 * **breaking** Minimum supported Node version is now Node 14
 * **breaking** Minimum supported TypeScript version is now 5 (it will likely work with lower versions, but we make no guarantess about that)
 * **breaking** Stricter types for `createEventDispatcher` (see PR for migration instructions) ([#7224](https://github.com/sveltejs/svelte/pull/7224))
+* **breaking** Stricter types for `Action` and `ActionReturn` (see PR for migration instructions) ([#7224](https://github.com/sveltejs/svelte/pull/7224))
 
 ## Unreleased (3.0)
 

src/runtime/internal/lifecycle.ts

@@ -57,6 +57,9 @@ export function onDestroy(fn: () => any) {
 }
 
 export interface EventDispatcher<EventMap extends Record<string, any>> {
+	// Implementation notes:
+	// - undefined extends X instead of X extends undefined makes this work better with both strict and nonstrict mode
+	// - [X] extends [never] is needed, X extends never would reduce the whole resulting type to never and not to one of the condition outcomes
 	<Type extends keyof EventMap>(
 		...args: [EventMap[Type]] extends [never] ? [type: Type, parameter?: null | undefined, options?: DispatchOptions] :
 		null extends EventMap[Type] ? [type: Type, parameter?: EventMap[Type], options?: DispatchOptions] :

test/types/actions.ts

@@ -0,0 +1,148 @@
+import type { Action, ActionReturn } from '$runtime/action';
+
+// ---------------- Action
+
+const href: Action<HTMLAnchorElement> = (node) => {
+    node.href = '';
+    // @ts-expect-error
+    node.href = 1;
+};
+href;
+
+const required: Action<HTMLElement, boolean> = (node, param) => {
+    node;
+    param;
+};
+required(null as any, true);
+// @ts-expect-error (only in strict mode) boolean missing
+required(null as any);
+// @ts-expect-error no boolean
+required(null as any, 'string');
+
+const required1: Action<HTMLElement, boolean> = (node, param) => {
+    node;
+    param;
+    return {
+        update: (p) => p === true,
+        destroy: () => {}
+    }
+};
+required1;
+
+const required2: Action<HTMLElement, boolean> = (node) => {
+    node;
+};
+required2;
+
+const required3: Action<HTMLElement, boolean> = (node, param) => {
+    node;
+    param;
+    return {
+        // @ts-expect-error comparison always resolves to false
+        update: (p) => p === 'd',
+        destroy: () => {}
+    }
+};
+required3;
+
+const optional: Action<HTMLElement, boolean | undefined> = (node, param?) => {
+    node;
+    param;
+};
+optional(null as any, true);
+optional(null as any);
+// @ts-expect-error no boolean
+optional(null as any, 'string');
+
+const optional1: Action<HTMLElement, boolean | undefined> = (node, param?) => {
+    node;
+    param;
+    return {
+        update: (p) => p === true,
+        destroy: () => {}
+    }
+};
+optional1;
+
+const optional2: Action<HTMLElement, boolean | undefined> = (node) => {
+    node;
+};
+optional2;
+
+const optional3: Action<HTMLElement, boolean | undefined> = (node, param) => {
+    node;
+    param;
+};
+optional3;
+
+const optional4: Action<HTMLElement, boolean | undefined> = (node, param?) => {
+    node;
+    param;
+    return {
+        // @ts-expect-error comparison always resolves to false
+        update: (p) => p === 'd',
+        destroy: () => {}
+    }
+};
+optional4;
+
+const no: Action<HTMLElement, never> = (node) => {
+    node;
+};
+// @ts-expect-error second param
+no(null as any, true);
+no(null as any);
+// @ts-expect-error second param
+no(null as any, 'string');
+
+const no1: Action<HTMLElement, never> = (node) => {
+    node;
+    return {
+        destroy: () => {}
+    }
+};
+no1;
+
+// @ts-expect-error param given
+const no2: Action<HTMLElement, never> = (node, param?) => {}
+
+// @ts-expect-error param given
+const no3: Action<HTMLElement, never> = (node, param) => {}
+
+// @ts-expect-error update method given
+const no4: Action<HTMLElement, never> = (node) => {
+    return {
+        update: () => {},
+        destroy: () => {}
+    }
+}
+
+// ---------------- ActionReturn
+
+const requiredReturn: ActionReturn<string> = {
+    update: (p) => p.toString(),
+};
+requiredReturn;
+
+const optionalReturn: ActionReturn<boolean | undefined> = {
+    update: (p) => {
+        p === true;
+        // @ts-expect-error could be undefined
+        p.toString();
+    },
+};
+optionalReturn;
+
+const invalidProperty: ActionReturn = {
+    // @ts-expect-error invalid property
+    invalid: () => {},
+};
+invalidProperty;
+
+type Attributes = ActionReturn<never, { a: string; }>['$$_attributes'];
+const attributes: Attributes = { a: 'a' };
+attributes;
+// @ts-expect-error wrong type
+const invalidAttributes1: Attributes = { a: 1 };
+// @ts-expect-error missing prop
+const invalidAttributes2: Attributes = {};