fix: no error assigning to a `const` property (#7966)

Fixes #7964
currently for a case where the parent type is ArrayPattern code needs to check if the elements are of direct type MemberExpression or Identifier, in the case of MemberExpression there will be an Identifier check for the Object of the MemberExpression.

---------

Co-authored-by: Yuichiro Yamashita <xydybaseball@gmail.com>

src/compiler/compile/Component.ts

@@ -794,20 +794,31 @@ export default class Component {
 				}
 
 				let deep = false;
-				let names: string[] | undefined; 
+				let names: string[] = [];
 
 				if (node.type === 'AssignmentExpression') {
-					deep = node.left.type === 'MemberExpression';
-					names = deep
-						? [get_object(node.left).name]
-						: extract_names(node.left);
+					if (node.left.type === 'ArrayPattern') {
+						walk(node.left, {
+							enter(node: Node, parent: Node) {
+								if (node.type === 'Identifier' &&
+									parent.type !== 'MemberExpression' &&
+									(parent.type !== 'AssignmentPattern' || parent.right !== node)) {
+										names.push(node.name);
+								}
+							}
+						});
+					} else {
+						deep = node.left.type === 'MemberExpression';
+						names = deep
+							? [get_object(node.left).name]
+							: extract_names(node.left);
+					}
 				} else if (node.type === 'UpdateExpression') {
 					deep = node.argument.type === 'MemberExpression';
 					const { name } = get_object(node.argument);
-					names = [name];
+					names.push(name);
 				}
-
-				if (names) {
+				if (names.length > 0) {
 					names.forEach(name => {
 						let current_scope = scope;
 						let declaration;

test/runtime/samples/assignment-to-const1/_config.js

@@ -0,0 +1,3 @@
+export default {
+	html: '<p>2, 1</p>'
+};

test/runtime/samples/assignment-to-const1/main.svelte

@@ -0,0 +1,6 @@
+<script>
+	const arr = [1, 2];
+	[arr[0], arr[1]] = [arr[1], arr[0]];
+</script>
+
+<p>{arr[0]}, {arr[1]}</p>

test/runtime/samples/assignment-to-const2/_config.js

@@ -0,0 +1,3 @@
+export default {
+	html: '<p>[{"a":2},100]</p>'
+};

test/runtime/samples/assignment-to-const2/main.svelte

@@ -0,0 +1,7 @@
+<script>
+	const a = 100;
+	const arr = [{ a: 1 }, 2];
+	[arr[0].a, arr[1] = a] = [arr[1]];
+</script>
+
+<p>{JSON.stringify(arr)}</p>

test/validator/samples/assignment-to-const-5/errors.json

@@ -0,0 +1,17 @@
+[
+	{
+		"code": "assignment-to-const",
+		"message": "You are assigning to a const",
+		"start": {
+			"line": 3,
+			"column": 1,
+			"character": 31
+		},
+		"end": {
+			"line": 3,
+			"column": 33,
+			"character": 63
+		},
+		"pos": 31
+	}
+]

test/validator/samples/assignment-to-const-5/input.svelte

@@ -0,0 +1,6 @@
+<script>
+	const arr = [1, 2];
+	[arr, arr[1]] = [arr[1], arr[0]];
+</script>
+
+{arr}

test/validator/samples/assignment-to-const-6/errors.json

@@ -0,0 +1 @@
+[]

test/validator/samples/assignment-to-const-6/input.svelte

@@ -0,0 +1,6 @@
+<script>
+	const arr = [1, 2];
+	[arr[0], arr[1]] = [arr[1], arr[0]];
+</script>
+
+{arr}

test/validator/samples/assignment-to-const-7/errors.json

@@ -0,0 +1,17 @@
+[
+	{
+		"code": "assignment-to-const",
+		"message": "You are assigning to a const",
+		"start": {
+			"line": 3,
+			"column": 1,
+			"character": 43
+		},
+		"end": {
+			"line": 3,
+			"column": 42,
+			"character": 84
+		},
+		"pos": 43
+	}
+]

test/validator/samples/assignment-to-const-7/input.svelte

@@ -0,0 +1,6 @@
+<script>
+	const arr = [{1: {arr: 2}}, 2];
+	[{1: { arr }}, arr[1]] = [arr[1], arr[0]];
+</script>
+
+{arr}

test/validator/samples/assignment-to-const-8/errors.json

@@ -0,0 +1 @@
+[]

test/validator/samples/assignment-to-const-8/input.svelte

@@ -0,0 +1,6 @@
+<script>
+	const arr = [1, 2];
+	[arr[0], arr[1] = arr] = [arr[1], arr[0]];
+</script>
+
+{arr}