fix

packages/svelte/src/compiler/phases/2-analyze/visitors/ClassBody.js

@@ -64,9 +64,7 @@ export function ClassBody(node, context) {
 				key: key.type === 'PrivateIdentifier' ? key : null,
 				value: /** @type {CallExpression} */ (value)
 			};
-		}
 
-		if (value) {
 			seen.push(name);
 		}
 	}

packages/svelte/tests/validator/samples/class-state-constructor-8/errors.json

@@ -1,14 +1,14 @@
 [
 	{
-		"code": "state_field_duplicate",
+		"code": "state_field_invalid_assignment",
-		"message": "`count` has already been declared on this class",
+		"message": "Cannot assign to a state field before its declaration",
 		"start": {
-			"line": 4,
+			"line": 3,
 			"column": 2
 		},
 		"end": {
-			"line": 4,
+			"line": 3,
-			"column": 24
+			"column": 17
 		}
 	}
 ]