unskip and fix test

Author: Rich-Harris

documentation/docs/98-reference/.generated/compile-errors.md

@@ -872,6 +872,12 @@ class Counter {
 
 ...but it can only happen once.
 
+### state_field_invalid_assignment
+
+```
+Cannot assign to a state field before its declaration
+```
+
 ### state_invalid_export
 
 ```

packages/svelte/messages/compile-errors/script.md

@@ -236,6 +236,10 @@ class Counter {
 
 ...but it can only happen once.
 
+## state_field_invalid_assignment
+
+> Cannot assign to a state field before its declaration
+
 ## state_invalid_export
 
 > Cannot export state from a module if it is reassigned. Either export a function returning the state value or only mutate the state value's properties

packages/svelte/src/compiler/errors.js

@@ -104,16 +104,6 @@ export function constant_binding(node, thing) {
 	e(node, 'constant_binding', `Cannot bind to ${thing}\nhttps://svelte.dev/e/constant_binding`);
 }
 
-/**
- * `%name%` has already been declared on this class
- * @param {null | number | NodeLike} node
- * @param {string} name
- * @returns {never}
- */
-export function state_field_duplicate(node, name) {
-	e(node, 'state_field_duplicate', `\`${name}\` has already been declared on this class\nhttps://svelte.dev/e/state_field_duplicate`);
-}
-
 /**
  * `%name%` has already been declared
  * @param {null | number | NodeLike} node
@@ -471,6 +461,25 @@ export function snippet_parameter_assignment(node) {
 	e(node, 'snippet_parameter_assignment', `Cannot reassign or bind to snippet parameter\nhttps://svelte.dev/e/snippet_parameter_assignment`);
 }
 
+/**
+ * `%name%` has already been declared on this class
+ * @param {null | number | NodeLike} node
+ * @param {string} name
+ * @returns {never}
+ */
+export function state_field_duplicate(node, name) {
+	e(node, 'state_field_duplicate', `\`${name}\` has already been declared on this class\nhttps://svelte.dev/e/state_field_duplicate`);
+}
+
+/**
+ * Cannot assign to a state field before its declaration
+ * @param {null | number | NodeLike} node
+ * @returns {never}
+ */
+export function state_field_invalid_assignment(node) {
+	e(node, 'state_field_invalid_assignment', `Cannot assign to a state field before its declaration\nhttps://svelte.dev/e/state_field_invalid_assignment`);
+}
+
 /**
  * Cannot export state from a module if it is reassigned. Either export a function returning the state value or only mutate the state value's properties
  * @param {null | number | NodeLike} node

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

@@ -8,7 +8,7 @@ import { validate_assignment } from './shared/utils.js';
  * @param {Context} context
  */
 export function AssignmentExpression(node, context) {
-	validate_assignment(node, node.left, context.state);
+	validate_assignment(node, node.left, context);
 
 	if (context.state.reactive_statement) {
 		const id = node.left.type === 'MemberExpression' ? object(node.left) : node.left;

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

@@ -158,7 +158,7 @@ export function BindDirective(node, context) {
 		return;
 	}
 
-	validate_assignment(node, node.expression, context.state);
+	validate_assignment(node, node.expression, context);
 
 	const assignee = node.expression;
 	const left = object(assignee);

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

@@ -8,7 +8,7 @@ import { validate_assignment } from './shared/utils.js';
  * @param {Context} context
  */
 export function UpdateExpression(node, context) {
-	validate_assignment(node, node.argument, context.state);
+	validate_assignment(node, node.argument, context);
 
 	if (context.state.reactive_statement) {
 		const id = node.argument.type === 'MemberExpression' ? object(node.argument) : node.argument;

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

@@ -4,24 +4,25 @@
 /** @import { Scope } from '../../../scope' */
 /** @import { NodeLike } from '../../../../errors.js' */
 import * as e from '../../../../errors.js';
-import { extract_identifiers } from '../../../../utils/ast.js';
+import { extract_identifiers, get_parent } from '../../../../utils/ast.js';
 import * as w from '../../../../warnings.js';
 import * as b from '#compiler/builders';
 import { get_rune } from '../../../scope.js';
+import { get_name } from '../../../nodes.js';
 
 /**
  * @param {AssignmentExpression | UpdateExpression | AST.BindDirective} node
  * @param {Pattern | Expression} argument
- * @param {AnalysisState} state
+ * @param {Context} context
  */
-export function validate_assignment(node, argument, state) {
-	validate_no_const_assignment(node, argument, state.scope, node.type === 'BindDirective');
+export function validate_assignment(node, argument, context) {
+	validate_no_const_assignment(node, argument, context.state.scope, node.type === 'BindDirective');
 
 	if (argument.type === 'Identifier') {
-		const binding = state.scope.get(argument.name);
+		const binding = context.state.scope.get(argument.name);
 
-		if (state.analysis.runes) {
-			if (binding?.node === state.analysis.props_id) {
+		if (context.state.analysis.runes) {
+			if (binding?.node === context.state.analysis.props_id) {
 				e.constant_assignment(node, '$props.id()');
 			}
 
@@ -34,6 +35,41 @@ export function validate_assignment(node, argument, state) {
 			e.snippet_parameter_assignment(node);
 		}
 	}
+
+	if (argument.type === 'MemberExpression' && argument.object.type === 'ThisExpression') {
+		const name =
+			argument.computed && argument.property.type !== 'Literal'
+				? null
+				: get_name(argument.property);
+
+		const field =
+			name !== null &&
+			context.state.state_fields &&
+			Object.hasOwn(context.state.state_fields, name) &&
+			context.state.state_fields[name];
+
+		// check we're not assigning to a state field before its declaration in the constructor
+		if (field && field.node.type === 'AssignmentExpression' && node !== field.node) {
+			let i = context.path.length;
+			while (i--) {
+				const parent = context.path[i];
+
+				if (
+					parent.type === 'FunctionDeclaration' ||
+					parent.type === 'FunctionExpression' ||
+					parent.type === 'ArrowFunctionExpression'
+				) {
+					const grandparent = get_parent(context.path, i - 1);
+
+					if (grandparent.type === 'MethodDefinition' && grandparent.kind === 'constructor') {
+						e.state_field_invalid_assignment(node);
+					}
+
+					break;
+				}
+			}
+		}
+	}
 }
 
 /**

packages/svelte/tests/validator/samples/class-state-constructor-9/_config.js

@@ -1,14 +1,14 @@
 [
 	{
-		"code": "state_field_duplicate",
-		"message": "`count` has already been declared on this class",
+		"code": "state_field_invalid_assignment",
+		"message": "Cannot assign to a state field before its declaration",
 		"start": {
-			"line": 7,
-			"column": 2
+			"line": 4,
+			"column": 3
 		},
 		"end": {
-			"line": 7,
-			"column": 24
+			"line": 4,
+			"column": 18
 		}
 	}
 ]