feat: throw error if module return invalid format

src/core/import-module.ts

@@ -21,7 +21,6 @@ export function esModuleInterop<T>(box?: T): T {
  * @return Promise with data.
  */
 export async function importModule<T = any>(path: string): Promise<T> {
-  // TODO: Source possibly empty or have invalid format.
   // TODO: Add diagnostic.
   const result = await import(path)
   return esModuleInterop(result)

src/core/theme-layers.ts

@@ -5,7 +5,7 @@ import deepmerge from 'deepmerge'
 import { Platforms, platforms } from './platforms'
 import { importModule } from './import-module'
 import { Shape, TokensMap, ThemeTokens, Meta } from './types'
-import { deepInvoke } from './utils'
+import { deepInvoke, throwError } from './utils'
 
 type ThemeLayers = Shape<
   Shape<
@@ -24,6 +24,9 @@ export async function getThemeLayers(
   const files = await fg(source)
   for (const fileName of files) {
     const source = await importModule(resolve(fileName))
+    if (typeof source !== 'function') {
+      throwError('Theme should return "withTokens" call.')
+    }
     const themeLayer = deepInvoke<ThemeTokens>(source)
     const { name } = parse(fileName)
     for (const [platform, levels] of platforms) {

src/core/utils.ts

@@ -21,3 +21,7 @@ export function withPrefix(value: string, prefix?: string): string {
   }
   return `${prefix}_${value}`
 }
+
+export function throwError(messag: string): void {
+  throw new Error(messag)
+}