next build command fails with some inner error

Bug report

Describe the bug

$ next build throws an error at optimization step:

Automatically optimizing pages...

> Build error occurred
[Error: ENOENT: no such file or directory, rename '/Users/username/Projects/projectname/.next/export/blog.html' -> 
'/Users/username/Projects/projectname/.next/serverless/pages/blog.html'] {
  errno: -2,
  code: 'ENOENT',
  syscall: 'rename',
  path: '/Users/username/Projects/projectname/.next/export/blog.html',
  dest: '/Users/username/Projects/projectname/.next/serverless/pages/blog.html'
}

for pages/blog/index.js file with the following getStaticProps

export async function getStaticProps() {
  let url = "/blog"
  let knex = await import("knex/client").then(m => m.default)
  let page = await knex("page")
    .select("title", "seoTitle", "body")
    .filter({url})
    .firstRequired()
  return {
    props: {page, ogType: "website"},
  }
}

It looks like some bug in NextJS build pipeline to me.

It started with recent NextJS and Now updates though I can’t tell the particular breaking update at this moment. Can it be related to Now CLI 19.0.0? I dunno how to downgrade this tool to an earlier version.

Extra info:

• It doesn’t happen with getServerSideProps or with purely static pages.
• It doesn’t happen with $ next dev.

To Reproduce

I can make a sandbox if necessary.

Expected behavior

next build should work 🤷

System information

• OSX
• Browser (if applies) [e.g. chrome, safari]
• Version of Next.js: tried with 9.3.5, 9.3.6, 9.3.7
• Version of Now: tried with 19.0.0, 19.0.1
• Version of Node.js: 12.16.3

Notes

Besides trying different NextJS versions I tried rm -rn node_modules and yarn cache clean. No effect on the bug.

[nummi]

Also running into this issue:

/pages/[uid].js
/pages/index.js

In getStaticPaths, I filter out index.

const pages = await ...

const paths = pages.results
  .filter((page) => {
    return page.uid !== 'index'
  })
  .map((page) => ({
    params: { uid: page.uid },
  }))

return {
  paths,
  fallback: true,
}

[ivan-kleshnin]

Update

The error is not a NextJS bug but rather a special case for which reporting can be improved.

I handle the same object at pages/blog/index.js as a blog page and, at the same time at pages/[...slugs].js as a generic page.

pages/[...slugs].js

export async function getStaticPaths() {
  return {
    paths: [... "/blog" ...] // among other things!
    fallback: true,
  }
}  

Which causes the above conflict. I’ll leave it up to you guys how to treat such cases. IMO they should be recognized and reported in some clear way.