fix: correctly determine bind:group members

- Previously, any each block parents where used as keys for the sub group. That's wrong, it should only be using each blocks whos declarations contribute to the `bind:group` expression. Fixes #10345
- Only the left-most identifier of the expression was used to determine the binding group. This is wrong, all identifiers within the expression need to be taken into account. Fixes #9947

Author: dummdidumm

.changeset/cyan-flowers-destroy.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: correctly determine `bind:group` members

packages/svelte/src/compiler/phases/2-analyze/index.js

@@ -1,9 +1,9 @@
 import is_reference from 'is-reference';
 import { walk } from 'zimmerframe';
 import { error } from '../../errors.js';
-import * as assert from '../../utils/assert.js';
 import {
 	extract_identifiers,
+	extract_all_identifiers_from_expression,
 	extract_paths,
 	is_event_attribute,
 	is_text_attribute,
@@ -1008,39 +1008,52 @@ const common_visitors = {
 
 		if (node.name !== 'group') return;
 
+		// Traverse the path upwards and find all EachBlocks who are (indirectly) contributing to bind:group,
+		// i.e. one of their declarations is referenced in the binding. This allows group bindings to work
+		// correctly when referencing a variable declared in an EachBlock by using the index of the each block
+		// entries as keys.
 		i = context.path.length;
+		const each_blocks = [];
+		const expression_ids = extract_all_identifiers_from_expression(node.expression);
+		let ids = expression_ids;
 		while (i--) {
 			const parent = context.path[i];
 			if (parent.type === 'EachBlock') {
-				parent.metadata.contains_group_binding = true;
-				for (const binding of parent.metadata.references) {
-					binding.mutated = true;
+				const references = ids.filter((id) => parent.metadata.declarations.has(id.name));
+				if (references.length > 0) {
+					parent.metadata.contains_group_binding = true;
+					for (const binding of parent.metadata.references) {
+						binding.mutated = true;
+					}
+					each_blocks.push(parent);
+					ids = ids.filter((id) => !references.includes(id));
+					ids.push(...extract_all_identifiers_from_expression(parent.expression));
 				}
 			}
 		}
 
-		const id = object(node.expression);
-
-		const binding = id === null ? null : context.state.scope.get(id.name);
-		assert.ok(binding);
-
-		let group = context.state.analysis.binding_groups.get(binding);
-		if (!group) {
-			group = {
-				name: context.state.scope.root.unique('binding_group'),
-				directives: []
-			};
-
-			context.state.analysis.binding_groups.set(binding, group);
+		// The identifiers that make up the binding expression form they key for the binding group.
+		// If the same identifiers in the same order are used in another bind:group, they will be in the same group.
+		// (there's an edge case where `bind:group={a[i]}` will be in a different group than `bind:group={a[j]}` even when i == j,
+		//  but this is a limitation of the current static analysis we do; it also never worked in Svelte 4)
+		const bindings = expression_ids.map((id) => context.state.scope.get(id.name));
+		let group_name;
+		outer: for (const [b, group] of context.state.analysis.binding_groups) {
+			if (b.length !== bindings.length) continue;
+			for (let i = 0; i < bindings.length; i++) {
+				if (bindings[i] !== b[i]) continue outer;
+			}
+			group_name = group;
 		}
 
-		group.directives.push(node);
+		if (!group_name) {
+			group_name = context.state.scope.root.unique('binding_group');
+			context.state.analysis.binding_groups.set(bindings, group_name);
+		}
 
 		node.metadata = {
-			binding_group_name: group.name,
-			parent_each_blocks: /** @type {import('#compiler').EachBlock[]} */ (
-				context.path.filter((p) => p.type === 'EachBlock')
-			)
+			binding_group_name: group_name,
+			parent_each_blocks: each_blocks
 		};
 	},
 	ArrowFunctionExpression: function_visitor,

packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js

@@ -2720,8 +2720,7 @@ export const template_visitors = {
 				case 'group': {
 					/** @type {import('estree').CallExpression[]} */
 					const indexes = [];
-					// we only care about the indexes above the first each block
-					for (const parent_each_block of node.metadata.parent_each_blocks.slice(0, -1)) {
+					for (const parent_each_block of node.metadata.parent_each_blocks) {
 						indexes.push(b.call('$.unwrap', parent_each_block.metadata.index));
 					}
 

packages/svelte/src/compiler/phases/scope.js

@@ -3,7 +3,7 @@ import { walk } from 'zimmerframe';
 import { is_element_node } from './nodes.js';
 import * as b from '../utils/builders.js';
 import { error } from '../errors.js';
-import { extract_identifiers, extract_identifiers_from_expression } from '../utils/ast.js';
+import { extract_identifiers, extract_identifiers_from_destructuring } from '../utils/ast.js';
 import { JsKeywords, Runes } from './constants.js';
 
 export class Scope {
@@ -306,7 +306,7 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 			scopes.set(attribute, scope);
 
 			if (attribute.expression) {
-				for (const id of extract_identifiers_from_expression(attribute.expression)) {
+				for (const id of extract_identifiers_from_destructuring(attribute.expression)) {
 					const binding = scope.declare(id, 'derived', 'const');
 					bindings.push(binding);
 				}
@@ -548,6 +548,7 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 				array_name: needs_array_deduplication ? state.scope.root.unique('$$array') : null,
 				index: scope.root.unique('$$index'),
 				item_name: node.context.type === 'Identifier' ? node.context.name : '$$item',
+				declarations: scope.declarations,
 				references: [...references_within]
 					.map((id) => /** @type {import('#compiler').Binding} */ (state.scope.get(id.name)))
 					.filter(Boolean),

packages/svelte/src/compiler/phases/types.d.ts

@@ -28,11 +28,6 @@ export interface ReactiveStatement {
 	dependencies: Set<Binding>;
 }
 
-export interface BindingGroup {
-	name: Identifier;
-	directives: BindDirective[];
-}
-
 export interface RawWarning {
 	code: string;
 	message: string;
@@ -72,7 +67,8 @@ export interface ComponentAnalysis extends Analysis {
 	/** If `true`, should append styles through JavaScript */
 	inject_styles: boolean;
 	reactive_statements: Map<LabeledStatement, ReactiveStatement>;
-	binding_groups: Map<Binding, BindingGroup>;
+	/** Identifiers that make up the `bind:group` expression -> internal group binding name */
+	binding_groups: Map<Array<Binding | null>, Identifier>;
 	slot_names: Set<string>;
 }
 

packages/svelte/src/compiler/types/template.d.ts

@@ -379,6 +379,7 @@ export interface EachBlock extends BaseNode {
 		array_name: Identifier | null;
 		index: Identifier;
 		item_name: string;
+		declarations: Map<string, Binding>;
 		/** List of bindings that are referenced within the expression */
 		references: Binding[];
 		/**

packages/svelte/src/compiler/utils/ast.js

@@ -1,3 +1,4 @@
+import { walk } from 'zimmerframe';
 import * as b from '../utils/builders.js';
 
 /**
@@ -96,11 +97,36 @@ export function extract_identifiers(param, nodes = []) {
 
 /**
  * Extracts all identifiers from an expression.
+ * @param {import('estree').Expression} expr
+ * @returns {import('estree').Identifier[]}
+ */
+export function extract_all_identifiers_from_expression(expr) {
+	/** @type {import('estree').Identifier[]} */
+	let nodes = [];
+
+	walk(
+		expr,
+		{},
+		{
+			Identifier(node, { path }) {
+				const parent = path.at(-1);
+				if (parent?.type !== 'MemberExpression' || parent.property !== node || parent.computed) {
+					nodes.push(node);
+				}
+			}
+		}
+	);
+
+	return nodes;
+}
+
+/**
+ * Extracts all leaf identifiers from a destructuring expression.
  * @param {import('estree').Identifier | import('estree').ObjectExpression | import('estree').ArrayExpression} node
  * @param {import('estree').Identifier[]} [nodes]
  * @returns
  */
-export function extract_identifiers_from_expression(node, nodes = []) {
+export function extract_identifiers_from_destructuring(node, nodes = []) {
 	// TODO This isn't complete, but it should be enough for our purposes
 	switch (node.type) {
 		case 'Identifier':
@@ -110,17 +136,17 @@ export function extract_identifiers_from_expression(node, nodes = []) {
 		case 'ObjectExpression':
 			for (const prop of node.properties) {
 				if (prop.type === 'Property') {
-					extract_identifiers_from_expression(/** @type {any} */ (prop.value), nodes);
+					extract_identifiers_from_destructuring(/** @type {any} */ (prop.value), nodes);
 				} else {
-					extract_identifiers_from_expression(/** @type {any} */ (prop.argument), nodes);
+					extract_identifiers_from_destructuring(/** @type {any} */ (prop.argument), nodes);
 				}
 			}
 
 			break;
 
 		case 'ArrayExpression':
 			for (const element of node.elements) {
-				if (element) extract_identifiers_from_expression(/** @type {any} */ (element), nodes);
+				if (element) extract_identifiers_from_destructuring(/** @type {any} */ (element), nodes);
 			}
 
 			break;

packages/svelte/tests/runtime-legacy/samples/binding-input-group-each-14/_config.js

@@ -0,0 +1,39 @@
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target, window }) {
+		const [input1, input2, input3, input4] = target.querySelectorAll('input');
+		const [p] = target.querySelectorAll('p');
+		const event = new window.Event('change');
+
+		input1.checked = true;
+		await input1.dispatchEvent(event);
+		await Promise.resolve();
+		assert.htmlEqual(p.innerHTML, '["1a"]');
+
+		input2.checked = true;
+		await input1.dispatchEvent(event);
+		await Promise.resolve();
+		assert.htmlEqual(p.innerHTML, '["1a","1b"]');
+
+		input3.checked = true;
+		await input1.dispatchEvent(event);
+		await Promise.resolve();
+		assert.htmlEqual(p.innerHTML, '["1a","1b","2a"]');
+
+		input4.checked = true;
+		await input1.dispatchEvent(event);
+		await Promise.resolve();
+		assert.htmlEqual(p.innerHTML, '["1a","1b","2a","2b"]');
+
+		input1.checked = false;
+		await input1.dispatchEvent(event);
+		await Promise.resolve();
+		assert.htmlEqual(p.innerHTML, '["1b","2a","2b"]');
+
+		input3.checked = false;
+		await input1.dispatchEvent(event);
+		await Promise.resolve();
+		assert.htmlEqual(p.innerHTML, '["1b","2b"]');
+	}
+});

packages/svelte/tests/runtime-legacy/samples/binding-input-group-each-14/main.svelte

@@ -0,0 +1,26 @@
+<script>
+	let group = [];
+	
+	const options = [
+		["1", ["1a", "1b"]],
+		["2", ["2a", "2b"]],
+	];
+</script>
+
+{#each options as [prefix, arr]}
+	{prefix}
+	<div>
+		{#each arr as item}
+			<label>
+				<input
+					type="checkbox"
+					bind:group
+					value={item}
+				/>
+				{item}
+			</label>
+		{/each}
+	</div>
+{/each}
+
+<p>{JSON.stringify(group)}</p>

packages/svelte/tests/runtime-legacy/samples/binding-input-group-each-15/_config.js

@@ -0,0 +1,23 @@
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const checkboxes = /** @type {NodeListOf<HTMLInputElement>} */ (
+			target.querySelectorAll('input[type="checkbox"]')
+		);
+
+		assert.isFalse(checkboxes[0].checked);
+		assert.isTrue(checkboxes[1].checked);
+		assert.isFalse(checkboxes[2].checked);
+
+		await checkboxes[1].click();
+
+		const noChecked = target.querySelector('#output')?.innerHTML;
+		assert.equal(noChecked, '');
+
+		await checkboxes[1].click();
+
+		const oneChecked = target.querySelector('#output')?.innerHTML;
+		assert.equal(oneChecked, 'Mint choc chip');
+	}
+});