Fix 6860: Warn user when binding rest operator

src/compiler/compile/compiler_warnings.ts

@@ -6,7 +6,7 @@
 export default {
 	custom_element_no_tag: {
 		code: 'custom-element-no-tag',
-		message: 'No custom element \'tag\' option was specified. To automatically register a custom element, specify a name with a hyphen in it, e.g. <svelte:options tag="my-thing"/>. To hide this warning, use <svelte:options tag={null}/>'			
+		message: 'No custom element \'tag\' option was specified. To automatically register a custom element, specify a name with a hyphen in it, e.g. <svelte:options tag="my-thing"/>. To hide this warning, use <svelte:options tag={null}/>'
 	},
 	unused_export_let: (component: string, property: string) => ({
 		code: 'unused-export-let',
@@ -143,5 +143,9 @@ export default {
 	redundant_event_modifier_passive: {
 		code: 'redundant-event-modifier',
 		message: 'The passive modifier only works with wheel and touch events'
-	}
+	},
+	invalid_rest_eachblock_binding: (rest_element_name: string) => ({
+		code: 'invalid-rest-eachblock-binding',
+		message: `...${rest_element_name} operator will create a new object and binding propogation with original object will not work`
+	})
 };

src/compiler/compile/nodes/EachBlock.ts

@@ -5,7 +5,7 @@ import AbstractBlock from './shared/AbstractBlock';
 import Element from './Element';
 import ConstTag from './ConstTag';
 import { Context, unpack_destructuring } from './shared/Context';
-import { Node } from 'estree';
+import { Node, Identifier } from 'estree';
 import Component from '../Component';
 import { TemplateNode } from '../../interfaces';
 import compiler_errors from '../compiler_errors';
@@ -28,7 +28,7 @@ export default class EachBlock extends AbstractBlock {
 	has_animation: boolean;
 	has_binding = false;
 	has_index_binding = false;
-
+	context_rest_properties: Map<string, Node>;
 	else?: ElseBlock;
 
 	constructor(component: Component, parent: Node, scope: TemplateScope, info: TemplateNode) {
@@ -40,10 +40,17 @@ export default class EachBlock extends AbstractBlock {
 		this.index = info.index;
 
 		this.scope = scope.child();
-
+		this.context_rest_properties = new Map();
 		this.contexts = [];
 		unpack_destructuring({ contexts: this.contexts, node: info.context, scope, component });
 
+		if (this.context_node.type === 'ObjectPattern') {
+			this.context_node.properties.forEach(i => {
+				if (i.type === 'RestElement') {
+					this.context_rest_properties.set((i.argument as Identifier).name, i);
+				}
+			});
+		}
 		this.contexts.forEach(context => {
 			this.scope.add(context.key.name, this.expression.dependencies, this);
 		});

src/compiler/compile/render_dom/wrappers/shared/mark_each_block_bindings.ts

@@ -2,6 +2,7 @@ import EachBlock from '../../../nodes/EachBlock';
 import InlineComponentWrapper from '../InlineComponent';
 import ElementWrapper from '../Element';
 import Binding from '../../../nodes/Binding';
+import compiler_warnings from '../../../compiler_warnings';
 
 export default function mark_each_block_bindings(
 	parent: ElementWrapper | InlineComponentWrapper,
@@ -11,6 +12,12 @@ export default function mark_each_block_bindings(
 	// the list and the index, if they're not otherwise referenced
 	binding.expression.references.forEach(name => {
 		const each_block = parent.node.scope.get_owner(name);
+		if (each_block && each_block.type === 'EachBlock') {
+			const rest_node = each_block.context_rest_properties.get(name);
+			if (rest_node) {
+				parent.renderer.component.warn(rest_node as any, compiler_warnings.invalid_rest_eachblock_binding(name));
+			}
+		}
 		if (each_block) {
 			(each_block as EachBlock).has_binding = true;
 		}

test/validator/samples/rest-eachblock-binding/input.svelte

@@ -0,0 +1,8 @@
+<script>
+	let objArray = [{foo: '1', id: 0, innerValue: "test"}, {foo: '2', id:1, innerValue: "Somethin"}]
+</script>
+
+{#each objArray as { id, ...rest } (id)}
+	<input bind:value={rest.innerValue} type="text" placeholder={rest.foo}/>
+	<br/>
+{/each}

test/validator/samples/rest-eachblock-binding/warnings.json

@@ -0,0 +1,6 @@
+[
+	{
+		"code": "invalid-rest-eachblock-binding",
+		"message": "...rest operator will create a new object and binding propogation with original object will not work"
+	}
+]