disallow computed state fields

packages/svelte/src/compiler/phases/2-analyze/visitors/shared/class-analysis.js

@@ -88,7 +88,7 @@ export class ClassAnalysis {
 				node.operator === '=' &&
 				node.left.type === 'MemberExpression' &&
 				node.left.object.type === 'ThisExpression' &&
-				(node.left.property.type === 'Identifier' ||
+				((node.left.property.type === 'Identifier' && !node.left.computed) ||
 					node.left.property.type === 'PrivateIdentifier' ||
 					node.left.property.type === 'Literal')
 			)

packages/svelte/tests/validator/samples/class-state-constructor-7/errors.json

@@ -0,0 +1,14 @@
+[
+	{
+		"code": "state_invalid_placement",
+		"message": "`$state(...)` can only be used as a variable declaration initializer, a class field declaration, or the first assignment to a class field at the top level of the constructor.",
+		"start": {
+			"line": 5,
+			"column": 16
+		},
+		"end": {
+			"line": 5,
+			"column": 25
+		}
+	}
+]

packages/svelte/tests/validator/samples/class-state-constructor-7/input.svelte.js

@@ -0,0 +1,7 @@
+const count = 'count';
+
+export class Counter {
+	constructor() {
+		this[count] = $state(0);
+	}
+}