feat: allow usage of getContext() within $derived runes (#13830)

Closes #13493.

This PR allows the usage of getContext() inside $derived runes. Previously, you could use it, but only on init and not updates – and this inconsistency was unnecessary. We can make it work just like we do in other places.

.changeset/beige-llamas-grab.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+feat: allow usage of getContext() within $derived runes

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

@@ -314,7 +314,7 @@ export function apply(
 
 	if (typeof handler === 'function') {
 		handler.apply(element, args);
-	} else if (has_side_effects || handler != null) {
+	} else if (has_side_effects || handler != null || error) {
 		const filename = component?.[FILENAME];
 		const location = loc ? ` at ${filename}:${loc[0]}:${loc[1]}` : ` in ${filename}`;
 

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

@@ -17,7 +17,8 @@ import {
 	skip_reaction,
 	update_reaction,
 	increment_version,
-	set_active_effect
+	set_active_effect,
+	component_context
 } from '../runtime.js';
 import { equals, safe_equals } from './equality.js';
 import * as e from '../errors.js';
@@ -44,6 +45,7 @@ export function derived(fn) {
 	/** @type {Derived<V>} */
 	const signal = {
 		children: null,
+		ctx: component_context,
 		deps: null,
 		equals,
 		f: flags,
@@ -169,5 +171,5 @@ export function destroy_derived(signal) {
 	set_signal_status(signal, DESTROYED);
 
 	// TODO we need to ensure we remove the derived from any parent derives
-	signal.v = signal.children = signal.deps = signal.reactions = null;
+	signal.v = signal.children = signal.deps = signal.ctx = signal.reactions = null;
 }

packages/svelte/src/internal/client/reactivity/types.d.ts

@@ -17,6 +17,8 @@ export interface Value<V = unknown> extends Signal {
 }
 
 export interface Reaction extends Signal {
+	/** The associated component context */
+	ctx: null | ComponentContext;
 	/** The reaction function */
 	fn: null | Function;
 	/** Signals that this signal reads from */
@@ -40,8 +42,6 @@ export interface Effect extends Reaction {
 	 */
 	nodes_start: null | TemplateNode;
 	nodes_end: null | TemplateNode;
-	/** The associated component context */
-	ctx: null | ComponentContext;
 	/** Reactions created inside this signal */
 	deriveds: null | Derived[];
 	/** The effect function */

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

@@ -302,6 +302,7 @@ export function update_reaction(reaction) {
 	var previous_reaction = active_reaction;
 	var previous_skip_reaction = skip_reaction;
 	var prev_derived_sources = derived_sources;
+	var previous_component_context = component_context;
 	var flags = reaction.f;
 
 	new_deps = /** @type {null | Value[]} */ (null);
@@ -310,6 +311,7 @@ export function update_reaction(reaction) {
 	active_reaction = (flags & (BRANCH_EFFECT | ROOT_EFFECT)) === 0 ? reaction : null;
 	skip_reaction = !is_flushing_effect && (flags & UNOWNED) !== 0;
 	derived_sources = null;
+	component_context = reaction.ctx;
 
 	try {
 		var result = /** @type {Function} */ (0, reaction.fn)();
@@ -347,6 +349,7 @@ export function update_reaction(reaction) {
 		active_reaction = previous_reaction;
 		skip_reaction = previous_skip_reaction;
 		derived_sources = prev_derived_sources;
+		component_context = previous_component_context;
 	}
 }
 
@@ -422,7 +425,6 @@ export function update_effect(effect) {
 	var previous_component_context = component_context;
 
 	active_effect = effect;
-	component_context = effect.ctx;
 
 	if (DEV) {
 		var previous_component_fn = dev_current_component_function;
@@ -449,7 +451,6 @@ export function update_effect(effect) {
 		handle_error(/** @type {Error} */ (error), effect, previous_component_context);
 	} finally {
 		active_effect = previous_effect;
-		component_context = previous_component_context;
 
 		if (DEV) {
 			dev_current_component_function = previous_component_fn;

packages/svelte/tests/runtime-runes/samples/derived-get-context/Child.svelte

@@ -0,0 +1,13 @@
+<script>
+	import { getContext } from 'svelte'
+
+	let count = $state(0);
+	let total = $derived(multiply(count));
+
+	function multiply(num) {
+		const context = getContext("key");
+		return num * context;
+	}
+</script>
+
+<button onclick={() => count++}>{total}</button>

packages/svelte/tests/runtime-runes/samples/derived-get-context/_config.js

@@ -0,0 +1,16 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<button>0</button>`,
+
+	test({ assert, target }) {
+		const btn = target.querySelector('button');
+
+		flushSync(() => {
+			btn?.click();
+		});
+
+		assert.htmlEqual(target.innerHTML, `<button>10</button>`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/derived-get-context/main.svelte

@@ -0,0 +1,8 @@
+<script>
+	import { setContext } from 'svelte'
+	import Child from './Child.svelte'
+	setContext("key", 10)
+</script>
+
+<Child />
+

packages/svelte/tests/runtime-runes/samples/event-handler-component-invalid-warning/_config.js

@@ -8,8 +8,24 @@ export default test({
 	},
 
 	test({ assert, target, warnings }) {
+		/** @type {any} */
+		let error;
+
+		const handler = (/** @type {any}} */ e) => {
+			error = e.error;
+			e.stopImmediatePropagation();
+		};
+
+		window.addEventListener('error', handler, true);
+
 		target.querySelector('button')?.click();
 
+		assert.throws(() => {
+			throw error;
+		}, /state_unsafe_mutation/);
+
+		window.removeEventListener('error', handler, true);
+
 		assert.deepEqual(warnings, [
 			'`click` handler at Button.svelte:5:9 should be a function. Did you mean to add a leading `() =>`?'
 		]);

packages/svelte/tests/runtime-runes/samples/event-handler-invalid-warning/_config.js

@@ -8,8 +8,24 @@ export default test({
 	},
 
 	test({ assert, target, warnings }) {
+		/** @type {any} */
+		let error;
+
+		const handler = (/** @type {any} */ e) => {
+			error = e.error;
+			e.stopImmediatePropagation();
+		};
+
+		window.addEventListener('error', handler, true);
+
 		target.querySelector('button')?.click();
 
+		assert.throws(() => {
+			throw error;
+		}, /state_unsafe_mutation/);
+
+		window.removeEventListener('error', handler, true);
+
 		assert.deepEqual(warnings, [
 			'`click` handler at main.svelte:9:17 should be a function. Did you mean to remove the trailing `()`?'
 		]);