fix: warn when providing non-serializable urls

Fixes #285

src/module.ts

@@ -551,7 +551,7 @@ declare module 'vue-router' {
               name: 'sitemap:urls',
               description: 'Set with the `sitemap.urls` config.',
             },
-            urls: await resolveUrls(config.urls),
+            urls: await resolveUrls(config.urls, { path: 'sitemap:urls', logger }),
           })
           // we want to avoid adding duplicates as well as hitting api endpoints multiple times
           resolvedConfigUrls = true
@@ -625,7 +625,7 @@ declare module 'vue-router' {
                 name: `sitemaps:${sitemapName}:urls`,
                 description: 'Set with the `sitemap.urls` config.',
               },
-              urls: await resolveUrls(definition.urls),
+              urls: await resolveUrls(definition.urls, { path: `sitemaps:${sitemapName}:urls`, logger }),
             })
             definition!.dynamicUrlsApiEndpoint && sitemapSources[sitemapName].push({
               context: {

src/util/nuxtSitemap.ts

@@ -4,15 +4,25 @@ import type { Nuxt } from '@nuxt/schema'
 import { useNuxt } from '@nuxt/kit'
 import { extname } from 'pathe'
 import { defu } from 'defu'
+import type { ConsolaInstance } from 'consola'
 import type { SitemapDefinition, SitemapUrl, SitemapUrlInput } from '../runtime/types'
 import { createPathFilter } from '../runtime/utils-pure'
 import type { CreateFilterOptions } from '../runtime/utils-pure'
 
-export async function resolveUrls(urls: Required<SitemapDefinition>['urls']): Promise<SitemapUrlInput[]> {
+export async function resolveUrls(urls: Required<SitemapDefinition>['urls'], ctx: { logger: ConsolaInstance, path: string }): Promise<SitemapUrlInput[]> {
   if (typeof urls === 'function')
     urls = urls()
   // resolve promise
   urls = await urls
+  // we need to validate that the urls can be serialised properly for example to avoid circular references
+  try {
+    urls = JSON.parse(JSON.stringify(urls))
+  }
+  catch (e) {
+    ctx.logger.warn(`Failed to serialize ${typeof urls} \`${ctx.path}\`, please make sure that the urls resolve as a valid array without circular dependencies.`)
+    ctx.logger.error(e)
+    return []
+  }
   return urls
 }