Hi Reza,
I believe local-file should import (guix utils) and use current-source-directory. Something like:
(define %cwd (current-source-directory))
(let ([...] (version-file (string-append %cwd "/VERSION")) [...] (source (local-file (string-append %cwd "/../..") "my-package-checkout" [...]
The current directory may not be where the VERSION file is.
giacomo