fix: support for new ConstTag node

Author: ota-meshi

src/context/script-let.ts

@@ -246,11 +246,11 @@ export class ScriptLetContext {
   }
 
   public addVariableDeclarator(
-    expression: ESTree.AssignmentExpression,
+    declarator: ESTree.VariableDeclarator | ESTree.AssignmentExpression,
     parent: SvelteNode,
     ...callbacks: ScriptLetCallback<ESTree.VariableDeclarator>[]
   ): ScriptLetCallback<ESTree.VariableDeclarator>[] {
-    const range = getNodeRange(expression);
+    const range = getNodeRange(declarator);
     const part = this.ctx.code.slice(...range);
     this.appendScript(
       `const ${part};`,

src/parser/compat.ts

@@ -204,7 +204,6 @@ export function getThenFromAwaitBlock(
   }
   return then.skip ? null : then;
 }
-
 export function getCatchFromAwaitBlock(
   block: SvAST.AwaitBlock | Compiler.AwaitBlock,
 ): Compiler.Fragment | SvAST.CatchBlock | null {
@@ -217,3 +216,15 @@ export function getCatchFromAwaitBlock(
   }
   return catchFragment.skip ? null : catchFragment;
 }
+
+// ConstTag
+export function getDeclaratorFromConstTag(
+  node: SvAST.ConstTag | Compiler.ConstTag,
+):
+  | ESTree.AssignmentExpression
+  | Compiler.ConstTag["declaration"]["declarations"][0] {
+  return (
+    (node as Compiler.ConstTag).declaration?.declarations?.[0] ??
+    (node as SvAST.ConstTag).expression
+  );
+}

src/parser/converts/const.ts

@@ -1,10 +1,12 @@
 import type { SvelteConstTag } from "../../ast";
 import type { Context } from "../../context";
+import { getDeclaratorFromConstTag } from "../compat";
 import type * as SvAST from "../svelte-ast-types";
+import type * as Compiler from "svelte/compiler";
 
 /** Convert for ConstTag */
 export function convertConstTag(
-  node: SvAST.ConstTag,
+  node: SvAST.ConstTag | Compiler.ConstTag,
   parent: SvelteConstTag["parent"],
   ctx: Context,
 ): SvelteConstTag {
@@ -15,7 +17,7 @@ export function convertConstTag(
     ...ctx.getConvertLocation(node),
   };
   ctx.scriptLet.addVariableDeclarator(
-    node.expression,
+    getDeclaratorFromConstTag(node),
     mustache,
     (declaration) => {
       mustache.declaration = declaration;