fix: ensure uniqueness of form.for(...) across form functions (#14327)

Fixes #14305

Author: dummdidumm

.changeset/thin-hornets-read.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: ensure uniqueness of `form.for(...)` across form functions

packages/kit/src/runtime/app/server/remote/form.js

@@ -108,14 +108,15 @@ export function form(fn) {
 				/** @type {RemoteForm<any>['for']} */
 				value: (key) => {
 					const { state } = get_request_store();
-					let instance = (state.form_instances ??= new Map()).get(key);
+					const cache_key = __.id + '|' + JSON.stringify(key);
+					let instance = (state.form_instances ??= new Map()).get(cache_key);
 
 					if (!instance) {
 						instance = create_instance(key);
 						instance.__.id = `${__.id}/${encodeURIComponent(JSON.stringify(key))}`;
 						instance.__.name = __.name;
 
-						state.form_instances.set(key, instance);
+						state.form_instances.set(cache_key, instance);
 					}
 
 					return instance;

packages/kit/test/apps/basics/src/routes/remote/form/+page.svelte

@@ -85,3 +85,9 @@
 		<button id="submit-btn-item-{item}">Task One for {item}</button>
 	</form>
 {/each}
+
+<form {...task_two.for('foo')}>
+	<span id="form-result-2-foo">{task_two.for('foo').result}</span>
+	<input name="task" value="foo2" />
+	<button id="submit-btn-item-2-foo">Task Two for foo</button>
+</form>

packages/kit/test/apps/basics/test/test.js

@@ -1640,12 +1640,17 @@ test.describe('remote functions', () => {
 		);
 	});
 
-	test('form.for(...) scopes form submission', async ({ page }) => {
+	test('form.for(...) scopes form submission', async ({ page, javaScriptEnabled }) => {
 		await page.goto('/remote/form');
 		await page.click('#submit-btn-item-foo');
 		await expect(page.locator('#form-result-foo')).toHaveText('foo');
 		await expect(page.locator('#form-result-bar')).toHaveText('');
 		await expect(page.locator('#form-result-1')).toHaveText('');
+
+		await page.click('#submit-btn-item-2-foo');
+		await expect(page.locator('#form-result-2-foo')).toHaveText('foo2');
+		await expect(page.locator('#form-result-foo')).toHaveText(javaScriptEnabled ? 'foo' : '');
+		await expect(page.locator('#form-result-2')).toHaveText('');
 	});
 
 	test('prerendered entries not called in prod', async ({ page, clicknav }) => {