No cradle found for filename.hs. Proceeding with implicit cradle

If you have 2 files ./app/Main.hs and ./test/Spec.hs, you can create a hie.yaml at the workspace root . with:

cradle:
  multi:
    - path: "./"
      config:
        cradle:
          stack:
            - path: "./app/Main.hs"
            - path: "./test/Spec.hs"

This should silence the error. Also, having stack in the system path is enough.

Bob and Maksim are right. For completeness sake I would add that I found https://github.com/mpickering/hie-bios to be of interest, and that a minimal hie.yaml containing

cradle:
  stack:

can work for a simple project.

you can try create file "hie.yaml" to your project and write in "hie.yaml": cradle: stack: