Re: [PATCH] profiles: Generate GHC's package database cache.

[Mark H Weaver <mhw@netris.org>]

Federico Beffa <beffa@ieee.org> writes:

> From dfe3b875267731006512b8a9803aaa56f07db12e Mon Sep 17 00:00:00 2001
> From: Federico Beffa <beffa@fbengineering.ch>
> Date: Sat, 4 Apr 2015 22:51:13 +0200
> Subject: [PATCH] profiles: Generate GHC's package database cache.

[...]

> +(define (ghc-package-cache-file manifest)
> +  "Return a derivation that builds the GHC 'package.cache' file for all the
> +entries of MANIFEST."
> +  (define ghc                                 ;lazy reference
> +    (module-ref (resolve-interface '(gnu packages haskell)) 'ghc))
> +
> +  (define build
> +    #~(begin 
> +        (use-modules (guix build utils)
> +                     (srfi srfi-1) (srfi srfi-26)
> +                     (ice-9 ftw))
> +
> +        (define ghc-name-version
> +          (let* ((base (basename #+ghc)))
> +            (string-drop base
> +                         (+ 1 (string-index base #\-)))))
> +        
> +        (define db-subdir
> +          (string-append "lib/" ghc-name-version "/package.conf.d"))
> +
> +        (define db-dir
> +          (string-append #$output "/" db-subdir))
> +        
> +        (define (conf-files top)
> +          (find-files (string-append top "/" db-subdir) "\\.conf$"))
> +
> +        (define (copy-conf-file conf)
> +          (let ((base (basename conf)))
> +            (copy-file conf (string-append db-dir "/" base))))
> +        
> +        (system* (string-append #+ghc "/bin/ghc-pkg") "init" db-dir)
> +        (for-each copy-conf-file
> +                  (append-map conf-files
> +                              '#$(manifest-inputs manifest)))
> +        (let ((success
> +               (zero?
> +                (system* (string-append #+ghc "/bin/ghc-pkg") "recache"
> +                         (string-append "--package-db=" db-dir)))))
> +          (for-each delete-file (find-files db-dir "\\.conf$"))
> +          success)))
> +
> +  ;; Don't depend on GHC when there's nothing to do.
> +  (if (null? (manifest-entries manifest))
> +      (gexp->derivation "ghc-package-cache" #~(mkdir #$output))
> +      (gexp->derivation "ghc-package-cache" build
> +                        #:modules '((guix build utils))
> +                        #:local-build? #t)))

I believe this will require GHC to build *any* non-empty profile.  Since
GHC is only available on Intel platforms, this will break profile
building on MIPS and ARM.

Even on Intel platforms, I don't want to have to install GHC to build
profiles that don't contain any Haskell packages, especially since it
involves trusting the upstream binaries from GHC.

What if I want to use Hugs instead, or some other Haskell implementation
that is capable of being bootstrapped from source code.  Is GHC the only
tool that can do this job?

      Mark