fix(cli): generate ExternalObject type on demand

cli/src/build.ts

@@ -493,18 +493,6 @@ async function processIntermediateTypeFile(
     return idents
   }
 
-  const dtsHeader = `/* tslint:disable */
-/* eslint-disable */
-
-/* auto-generated by NAPI-RS */
-
-export class ExternalObject<T> {
-  readonly '': {
-    readonly '': unique symbol
-    [K: symbol]: T
-  }
-}\n`
-
   const allDefs = lines.map((line) => JSON.parse(line) as TypeDef)
 
   function convertDefs(defs: TypeDef[], nested = false): string {
@@ -597,8 +585,29 @@ export class ExternalObject<T> {
     return acc + `export namespace ${mod} {\n${convertDefs(defs, true)}}\n`
   }, '')
 
+  const dtsHeader = `/* tslint:disable */
+/* eslint-disable */
+
+/* auto-generated by NAPI-RS */\n
+`
+
+  const externalDef =
+    topLevelDef.indexOf('ExternalObject<') > -1 ||
+    namespaceDefs.indexOf('ExternalObject<') > -1
+      ? `export class ExternalObject<T> {
+  readonly '': {
+    readonly '': unique symbol
+    [K: symbol]: T
+  }
+}\n`
+      : ''
+
   await unlinkAsync(source)
-  await writeFileAsync(target, dtsHeader + topLevelDef + namespaceDefs, 'utf8')
+  await writeFileAsync(
+    target,
+    dtsHeader + externalDef + topLevelDef + namespaceDefs,
+    'utf8',
+  )
   return idents
 }