bug#72291: ‘guix pack -RR’ doesn’t support provide “fakechroot” engine for script

["Ludovic Courtès" <ludovic.courtes@inria.fr>]

Assume a manifest like this:

--8<---------------cut here---------------start------------->8---
(use-modules (guix))

(define program
  (program-file "hello" #~(display "hello")))

(define package-tree
  (computed-file "package-with-script"
                 #~(let ((bin (string-append #$output "/bin")))
                     (mkdir #$output)
                     (mkdir bin)
                     (copy-file #$program (string-append bin "/hello")))))

(manifest (list (manifest-entry
                  (name "hello")
                  (version "0")
                  (item package-tree))))
--8<---------------cut here---------------end--------------->8---

Passing it to ‘guix pack -RR -m’ yields a bundle where the “fakechroot”
execution engine is not supported for the ‘bin/hello’ script.

The explanation is in a TODO in (guix scripts pack):

    (define (elf-loader-compile-flags program)
      ;; Return the cpp flags defining macros for the ld.so/fakechroot
      ;; wrapper of PROGRAM.
      #$(if fakechroot?
            ;; TODO: Handle scripts by wrapping their interpreter.
            #~(if (elf-file? program)
                   …
                  '())
            #~'()))

I’m not entirely sure how to address it.

One workaround is to add ‘bash-minimal’ to the pack:

  guix pack -RR bash-minimal …

… and then, on the target machine, to run Bash first:

  GUIX_EXECUTION_ENGINE=fakechroot ./bin/sh -c ./bin/the-script

Ludo’.