Ludovic Courtès <ludo@gnu.org> writes:

[...]

>> +(define (purify-environment)
>> +  "Unset almost all environment variables.  A small number of variables such
>> +as 'HOME' and 'USER' are left untouched."
>> +  (for-each unsetenv
>> +            (filter (lambda (variable)
>> +                      ;; Protect some env vars from purification.  Borrowed
>> +                      ;; from nix-shell.
>> +                      (not (member variable
>> +                                   '("HOME" "USER" "LOGNAME" "DISPLAY"
>> +                                     "TERM" "TZ" "PAGER"))))
>> +                    (map car (get-environment-variables)))))
>
> Maybe put the list of env. vars in a global variable, say
> ‘%precious-variables’, and then:
>
>   (remove (cut member <> %precious-variables)
>           (match (get-environment-variables)
>             (((names . values) ...)
>              names)))
>
> (My allergy to ‘car’ goes this far.  ;-))
>

Done.  Very elegant.

>> +  (display (_ "
>> +  -e, --exec             shell command to execute"))
>
> Perhaps make it -E, and use -e consistently with ‘guix build’?  It may
> be possible to reuse ‘options/resolve-packages’ for that.
>

Done.  Flag changed to '-E', and '-e'/'--expression' flag added.  I
wrote my another version of 'options/resolve-packages' since my needs
are different than 'guix build'.

>> +(define %default-options
>> +  ;; Default to opening a new shell.
>> +  `((exec . ,(getenv "SHELL"))
>
> (or (getenv "SHELL") "/bin/sh")
>

Done.

>> +(define (build-inputs inputs opts)
>> +  "Build the packages in INPUTS using the build options in OPTS."
>> +  (with-store store
>> +    (run-with-store store
>> +      (mlet* %store-monad ((drvs (sequence %store-monad
>> +                                           (map package->derivation inputs))))
>> +        (mbegin %store-monad
>> +          (show-what-to-build* drvs
>> +                               #:use-substitutes? (assoc-ref opts 'substitutes?)
>> +                               #:dry-run? #f)
>> +          (set-build-options-from-command-line* opts)
>> +          (built-derivations drvs)
>> +          (return drvs))))))
>
> The store should rather be kept open around (system command).  Otherwise
> the above derivations and their outputs could be GC’d (it should be
> possible to check that by trying to run ‘guix gc -d XXX’ on one of them
> from within the sub-shell.)
>

Great point.  Done.

>> +;; Entry point.
>> +(define (guix-environment . args)
>> +  (define (parse-options)
>> +    (args-fold* args %options
>> +                (lambda (opt name arg result)
>> +                  (leave (_ "~A: unrecognized option~%") name))
>> +                (lambda (arg result)
>> +                  (alist-cons 'package arg result))
>> +                %default-options))
>> +
>> +  (let* ((opts (parse-options))
>> +         (pure? (assoc-ref opts 'pure))
>> +         (command (assoc-ref opts 'exec))
>> +         ;; Load from file if given, otherwise search for packages.
>> +         (inputs (packages->transitive-inputs
>> +                  (or (and=> (assoc-ref opts 'load) load)
>> +                      (map specification->package
>> +                           (pick-all opts 'package)))))
>> +         (drvs (build-inputs inputs opts)))
>
> Would be good to honor --dry-run as well.  It would just print what
> needs to be built and exit.
>

Done.

Updated patch attached.  Thanks for the feedback!