Clear up error message when production build is missing during next export

[timneutkens]

From @jlongster:

Problem #3: static export

I ran:

$ next export

I got this error:

Error: ENOENT: no such file or directory, open '/Users/james/tmp/devii/.next/BUILD_ID'
    at Object.openSync (fs.js:440:3)
    at readFileSync (fs.js:342:35)
    at exportApp (/Users/james/tmp/devii/node_modules/next/dist/export/index.js:2:919) {

Again you need to do next build first. Not clear at all.

When the export finally worked I got this output:

info  - using build directory: /Users/james/tmp/devii/.next
info  - Copying "static build" directory
info  - No "exportPathMap" found in "next.config.js". Generating map from "./pages"
info  - Launching 7 workers
info  - Copying "public" directory
info  - undefined (2/2)
Export successful

It doesn't tell me where it put the static export, and the undefined is off-putting (tweet). Turns out it puts it in the out folder

---

Notes from me:

Had a look at this and it turns out there's an edge case where it would throw this error when there is a .next folder but no production build (BUILD_ID missing).

The undefined part has been solved already in the latest version of Next.js (as replied on the tweet too).

The location not being available can be easily fixed 👍 Added it to #19777 as well

[balazsorban44]

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