Backpack fails with: Can't find interface-file declaration
When using an indefinite module to fill in a signature, backpack succeeds. However, it fails later during instantiation with:
typecheckIfaceForInstantiate Declaration for write#: Can't find interface-file declaration for type constructor or class M Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error
At https://github.com/andrewthad/vex-minimal-reproducer, there is a somewhat minimal reproducer. The repo also includes a readme with more detail about the motivation and some investigation of the error itself.
Steps to reproduce
git clone https://github.com/andrewthad/vex-minimal-reproducer cd vex-minimal-reproducer cabal v2-build
The build should succeed.
- GHC version used: 8.8.3, 8.10.1rc, HEAD