angular NG6002: This import contains errors after upgrade

TL;DR

Run the build, read the underlying error inside the imported file, then upgrade the offending library to a version built for your Angular major. NG6002 means the Angular compiler found errors in something you imported, and after an upgrade that is usually a library still shipped in the old compilation format. Matching the library to your Angular version clears it.

error NG6002: This import contains errors, which may affect components without an explicit ngModule.

Steps

1. Run ng build (not just serve) and scroll to the first NG6002. Note the file it names. Expected: you can tell whether the flagged file is yours or a library file.

2. If it is a library: check its changelog or readme for supported Angular versions, and run npm ls @angular/core to confirm a single copy. Expected: you find the library predates your Angular major, or two Angular copies in the tree.

3. Upgrade the library to the release matching your Angular major. Delete node_modules and the lockfile, then reinstall. Expected: npm ls @angular/core shows one version matching your Angular.

4. If the flagged file is your own (e.g. a barrel re-export), fix the underlying TypeScript error the compiler reports just above the NG6002 line. Expected: the root error is gone, so the import error goes with it.

5. Rebuild with ng build. Expected: the build succeeds with no NG6002.

Use this when

• NG6002 appears right after an Angular major upgrade
• The error points into node_modules or a shared import rather than new code you wrote
• Multiple copies of @angular packages show up in the tree
• A library worked before the upgrade and nothing else changed

Not for this skill when

• NG6002 is caused by a plain TypeScript syntax error in your own new code (fix the syntax)
• The error is about an import that cannot be resolved at all (different error code, different fix)
• You are on Angular 13+ with a View Engine-only library and no upgrade exists (that needs replacing the library, not this checklist)

Variant phrasings

• angular NG6002 after upgrade
• This import contains errors ng build
• NG6002 library not compatible with angular version
• angular upgrade build fails on library import

Why it happens

The Angular compiler type-checks the whole import graph of your app. When a library was compiled with an older Angular (pre-Ivy format, or an older Ivy metadata version), the new compiler cannot read it cleanly and reports the import as erroneous. Your code did not change; the compiler got stricter and the library got stale.

Edge cases

• Two copies of @angular/core (app plus a linked library) produce phantom NG6002s. Dedupe first.
• tsconfig paths mappings can shadow a library with a stale local copy. Check them.
• Some libraries need specific module settings; check their install notes for your Angular major.
• If no compatible library release exists, the path is patching or replacing the library, not disabling the compiler checks.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_8YLYpgUuVT63l3JlumENzA