fix(gatsby-plugin-sitemap): fix pathPrefix handling (#34158)

Author: wardpeet

packages/gatsby-plugin-sitemap/src/__tests__/gatsby-node.js

@@ -141,14 +141,21 @@ describe(`gatsby-plugin-sitemap Node API`, () => {
     const options = {
       entryLimit: 1,
     }
+    const assetPrefix = `https://cdn.example.com`
     const prefix = `/test`
     await onPostBuild(
-      { graphql, pathPrefix: prefix, reporter },
+      {
+        graphql,
+        basePath: prefix,
+        pathPrefix: `${assetPrefix}${prefix}`,
+        reporter,
+      },
       await schema.validateAsync(options)
     )
     const { sourceData } = sitemap.simpleSitemapAndIndex.mock.calls[0][0]
     sourceData.forEach(page => {
       expect(page.url).toEqual(expect.stringContaining(prefix))
+      expect(page.url).not.toEqual(expect.stringContaining(assetPrefix))
     })
   })
 

packages/gatsby-plugin-sitemap/src/gatsby-node.js

@@ -6,7 +6,7 @@ import { prefixPath, pageFilter, REPORTER_PREFIX } from "./internals"
 exports.pluginOptionsSchema = pluginOptionsSchema
 
 exports.onPostBuild = async (
-  { graphql, reporter, pathPrefix },
+  { graphql, reporter, basePath, pathPrefix },
   {
     output,
     entryLimit,
@@ -70,7 +70,7 @@ exports.onPostBuild = async (
         serialize(page, { resolvePagePath })
       )
       serializedPages.push({
-        url: prefixPath({ url, siteUrl, pathPrefix }),
+        url: prefixPath({ url, siteUrl, pathPrefix: basePath }),
         ...rest,
       })
     } catch (err) {