use expression directly

packages/svelte/src/compiler/phases/1-parse/state/tag.js

@@ -573,14 +573,7 @@ function special(parser) {
 				type: 'ConstTag',
 				start,
 				end: parser.index,
-				expression: {
-					type: 'AssignmentExpression',
-					start: (declaration.start ?? 0) + CONST_LENGTH,
-					end: declaration.end ?? 0,
-					operator: '=',
-					left: declaration.declarations[0].id,
-					right: declaration.declarations[0].init
-				}
+				declaration
 			})
 		);
 	}

packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js

@@ -1611,19 +1611,20 @@ export const template_visitors = {
 		);
 	},
 	ConstTag(node, { state, visit }) {
+		const declaration = node.declaration.declarations[0];
 		// TODO we can almost certainly share some code with $derived(...)
-		if (node.expression.left.type === 'Identifier') {
+		if (declaration.id.type === 'Identifier') {
 			state.init.push(
 				b.const(
-					node.expression.left,
+					declaration.id,
 					b.call(
 						'$.derived',
-						b.thunk(/** @type {import('estree').Expression} */ (visit(node.expression.right)))
+						b.thunk(/** @type {import('estree').Expression} */ (visit(declaration.init)))
 					)
 				)
 			);
 		} else {
-			const identifiers = extract_identifiers(node.expression.left);
+			const identifiers = extract_identifiers(declaration.id);
 			const tmp = b.id(state.scope.generate('computed_const'));
 
 			// Make all identifiers that are declared within the following computed regular
@@ -1639,8 +1640,8 @@ export const template_visitors = {
 				[],
 				b.block([
 					b.const(
-						/** @type {import('estree').Pattern} */ (visit(node.expression.left)),
-						/** @type {import('estree').Expression} */ (visit(node.expression.right))
+						/** @type {import('estree').Pattern} */ (visit(declaration.id)),
+						/** @type {import('estree').Expression} */ (visit(declaration.init))
 					),
 					b.return(b.object(identifiers.map((node) => b.prop('init', node, node))))
 				])

packages/svelte/src/compiler/phases/3-transform/server/transform-server.js

@@ -1049,8 +1049,9 @@ const template_visitors = {
 		state.template.push(t_expression(id));
 	},
 	ConstTag(node, { state, visit }) {
-		const pattern = /** @type {import('estree').Pattern} */ (visit(node.expression.left));
-		const init = /** @type {import('estree').Expression} */ (visit(node.expression.right));
+		const declaration = node.declaration.declarations[0];
+		const pattern = /** @type {import('estree').Pattern} */ (visit(declaration.id));
+		const init = /** @type {import('estree').Expression} */ (visit(declaration.init));
 		state.init.push(b.declaration('const', pattern, init));
 	},
 	DebugTag(node, { state, visit }) {

packages/svelte/src/compiler/phases/scope.js

@@ -437,7 +437,8 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 			next();
 		},
 
-		VariableDeclaration(node, { state, next }) {
+		VariableDeclaration(node, { state, path, next }) {
+			const is_parent_const_tag = path.at(-1)?.type === 'ConstTag';
 			for (const declarator of node.declarations) {
 				/** @type {import('#compiler').Binding[]} */
 				const bindings = [];
@@ -445,7 +446,12 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 				state.scope.declarators.set(declarator, bindings);
 
 				for (const id of extract_identifiers(declarator.id)) {
-					const binding = state.scope.declare(id, 'normal', node.kind, declarator.init);
+					const binding = state.scope.declare(
+						id,
+						is_parent_const_tag ? 'derived' : 'normal',
+						node.kind,
+						declarator.init
+					);
 					bindings.push(binding);
 				}
 			}
@@ -594,7 +600,8 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 		},
 
 		ConstTag(node, { state, next }) {
-			for (const identifier of extract_identifiers(node.expression.left)) {
+			const declaration = node.declaration.declarations[0];
+			for (const identifier of extract_identifiers(declaration.id)) {
 				state.scope.declare(
 					/** @type {import('estree').Identifier} */ (identifier),
 					'derived',

packages/svelte/src/compiler/types/template.d.ts

@@ -2,7 +2,8 @@ import type { Binding } from '#compiler';
 import type {
 	ArrayExpression,
 	ArrowFunctionExpression,
-	AssignmentExpression,
+	VariableDeclaration,
+	VariableDeclarator,
 	Expression,
 	FunctionDeclaration,
 	FunctionExpression,
@@ -11,8 +12,7 @@ import type {
 	Node,
 	ObjectExpression,
 	Pattern,
-	Program,
-	VariableDeclaration
+	Program
 } from 'estree';
 
 export interface BaseNode {
@@ -131,7 +131,9 @@ export interface Comment extends BaseNode {
 /** A `{@const ...}` tag */
 export interface ConstTag extends BaseNode {
 	type: 'ConstTag';
-	expression: AssignmentExpression;
+	declaration: VariableDeclaration & {
+		declarations: [VariableDeclarator & { id: Identifier, init: Expression } ]
+	};
 }
 
 /** A `{@debug ...}` tag */