Experimenting with array destructuring in each-blocks

src/compile/nodes/EachBlock.ts

@@ -9,14 +9,18 @@ import { Node as INode } from '../../interfaces';
 function unpack_destructuring(contexts: Array<{ name: string, tail: string }>, node: INode, tail: string) {
 	if (!node) return;
 
-	if (node.type === 'Identifier') {
+	if (node.type === 'Identifier' || node.type === 'RestIdentifier') {
 		contexts.push({
 			key: node,
 			tail
 		});
 	} else if (node.type === 'ArrayPattern') {
 		node.elements.forEach((element, i) => {
-			unpack_destructuring(contexts, element, `${tail}[${i}]`);
+			if (element.type === 'RestIdentifier') {
+				unpack_destructuring(contexts, element, `${tail}.slice(${i})`)
+			} else {
+				unpack_destructuring(contexts, element, `${tail}[${i}]`);
+			}
 		});
 	} else if (node.type === 'ObjectPattern') {
 		node.properties.forEach((property) => {

src/parse/read/context.ts

@@ -20,7 +20,7 @@ type Property = {
 type Context = {
 	start: number;
 	end: number;
-	type: 'Identifier' | 'ArrayPattern' | 'ObjectPattern';
+	type: 'Identifier' | 'ArrayPattern' | 'ObjectPattern' | 'RestIdentifier';
 	name?: string;
 	elements?: Context[];
 	properties?: Property[];
@@ -35,6 +35,13 @@ function error_on_assignment_pattern(parser: Parser) {
 	}
 }
 
+function error_on_rest_pattern_not_last(parser: Parser) {
+	parser.error({
+		code: 'rest-pattern-not-last',
+		message: 'Rest destructuring expected to be last'
+	}, parser.index);
+}
+
 export default function read_context(parser: Parser) {
 	const context: Context = {
 		start: parser.index,
@@ -49,6 +56,11 @@ export default function read_context(parser: Parser) {
 		do {
 			parser.allow_whitespace();
 
+			const lastContext = context.elements[context.elements.length - 1];
+			if (lastContext && lastContext.type === 'RestIdentifier') {
+				error_on_rest_pattern_not_last(parser);
+			}
+
 			if (parser.template[parser.index] === ',') {
 				context.elements.push(null);
 			} else {
@@ -103,6 +115,22 @@ export default function read_context(parser: Parser) {
 		context.end = parser.index;
 	}
 
+	else if (parser.eat('...')) {
+		const name = parser.read_identifier();
+		if (name) {
+			context.type = 'RestIdentifier';
+			context.end = parser.index;
+			context.name = name;
+		}
+
+		else {
+			parser.error({
+				code: 'invalid-context',
+				message: 'Expected a rest pattern'
+			});
+		}
+	}
+
 	else {
 		const name = parser.read_identifier();
 		if (name) {

test/parser/samples/each-block-destructured/input.svelte

@@ -1,3 +1,3 @@
-{#each animals as [key, value]}
+{#each animals as [key, value, ...rest]}
 	<p>{key}: {value}</p>
 {/each}

test/parser/samples/each-block-destructured/output.json

@@ -1,12 +1,12 @@
 {
 	"html": {
 		"start": 0,
-		"end": 62,
+		"end": 71,
 		"type": "Fragment",
 		"children": [
 			{
 				"start": 0,
-				"end": 62,
+				"end": 71,
 				"type": "EachBlock",
 				"expression": {
 					"type": "Identifier",
@@ -16,37 +16,37 @@
 				},
 				"children": [
 					{
-						"start": 33,
+						"start": 42,
-						"end": 54,
+						"end": 63,
 						"type": "Element",
 						"name": "p",
 						"attributes": [],
 						"children": [
 							{
-								"start": 36,
+								"start": 45,
-								"end": 41,
+								"end": 50,
 								"type": "MustacheTag",
 								"expression": {
 									"type": "Identifier",
-									"start": 37,
+									"start": 46,
-									"end": 40,
+									"end": 49,
 									"name": "key"
 								}
 							},
 							{
-								"start": 41,
+								"start": 50,
-								"end": 43,
+								"end": 52,
 								"type": "Text",
 								"data": ": "
 							},
 							{
-								"start": 43,
+								"start": 52,
-								"end": 50,
+								"end": 59,
 								"type": "MustacheTag",
 								"expression": {
 									"type": "Identifier",
-									"start": 44,
+									"start": 53,
-									"end": 49,
+									"end": 58,
 									"name": "value"
 								}
 							}
@@ -55,7 +55,7 @@
 				],
 				"context": {
 					"start": 18,
-					"end": 30,
+					"end": 39,
 					"type": "ArrayPattern",
 					"elements": [
 						{
@@ -69,6 +69,12 @@
 							"end": 29,
 							"type": "Identifier",
 							"name": "value"
+						},
+						{
+							"start": 31,
+							"end": 38,
+							"type": "RestIdentifier",
+							"name": "rest"
 						}
 					]
 				}