[jackhill/guix/guix.git] / guix / ui.scm

;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2013 Mark H Weaver <mhw@netris.org>
;;; Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
;;; Copyright © 2014 Cyril Roelandt <tipecaml@gmail.com>
;;; Copyright © 2014 Cyrill Schenkel <cyrill.schenkel@gmail.com>
;;; Copyright © 2014, 2015, 2017 Alex Kost <alezost@gmail.com>
;;; Copyright © 2015 David Thompson <davet@gnu.org>
;;; Copyright © 2015, 2016 Mathieu Lirzin <mthl@gnu.org>
;;; Copyright © 2016 Roel Janssen <roel@gnu.org>
;;; Copyright © 2016 Benz Schenk <benz.schenk@uzh.ch>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define-module (guix ui)
  #:use-module (guix i18n)
  #:use-module (guix gexp)
  #:use-module (guix sets)
  #:use-module (guix utils)
  #:use-module (guix store)
  #:use-module (guix config)
  #:use-module (guix packages)
  #:use-module (guix profiles)
  #:use-module (guix derivations)
  #:use-module (guix combinators)
  #:use-module (guix build-system)
  #:use-module (guix serialization)
  #:use-module ((guix licenses) #:select (license? license-name))
  #:use-module ((guix build syscalls)
                #:select (free-disk-space terminal-columns))
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-11)
  #:use-module (srfi srfi-19)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-31)
  #:use-module (srfi srfi-34)
  #:use-module (srfi srfi-35)
  #:autoload   (ice-9 ftw)  (scandir)
  #:use-module (ice-9 match)
  #:use-module (ice-9 format)
  #:use-module (ice-9 regex)
  #:autoload   (system base compile) (compile-file)
  #:autoload   (system repl repl)  (start-repl)
  #:autoload   (system repl debug) (make-debug stack->vector)
  #:use-module (texinfo)
  #:use-module (texinfo plain-text)
  #:use-module (texinfo string-utils)
  #:re-export (G_ N_ P_)                          ;backward compatibility
  #:export (report-error
            display-hint
            leave
            make-user-module
            load*
            warn-about-load-error
            show-version-and-exit
            show-bug-report-information
            make-regexp*
            string->number*
            size->number
            show-derivation-outputs
            show-what-to-build
            show-what-to-build*
            show-manifest-transaction
            call-with-error-handling
            with-error-handling
            leave-on-EPIPE
            read/eval
            read/eval-package-expression
            location->string
            fill-paragraph
            %text-width
            texi->plain-text
            package-description-string
            package-synopsis-string
            string->recutils
            package->recutils
            package-specification->name+version+output
            relevance
            package-relevance
            string->generations
            string->duration
            matching-generations
            display-generation
            display-profile-content
            display-profile-content-diff
            roll-back*
            switch-to-generation*
            delete-generation*
            run-guix-command
            run-guix
            program-name
            guix-warning-port
            warning
            info
            guix-main))

;;; Commentary:
;;;
;;; User interface facilities for command-line tools.
;;;
;;; Code:

(define-syntax-rule (define-diagnostic name prefix)
  "Create a diagnostic macro (i.e., NAME), which will prepend PREFIX to all
messages."
  (define-syntax name
    (lambda (x)
      (define (augmented-format-string fmt)
        (string-append "~:[~*~;guix ~a: ~]~a" (syntax->datum fmt)))

      (syntax-case x ()
        ((name (underscore fmt) args (... ...))
         (and (string? (syntax->datum #'fmt))
              (free-identifier=? #'underscore #'G_))
         (with-syntax ((fmt*   (augmented-format-string #'fmt))
                       (prefix (datum->syntax x prefix)))
           #'(format (guix-warning-port) (gettext fmt*)
                     (program-name) (program-name) prefix
                     args (... ...))))
        ((name (N-underscore singular plural n) args (... ...))
         (and (string? (syntax->datum #'singular))
              (string? (syntax->datum #'plural))
              (free-identifier=? #'N-underscore #'N_))
         (with-syntax ((s      (augmented-format-string #'singular))
                       (p      (augmented-format-string #'plural))
                       (prefix (datum->syntax x prefix)))
           #'(format (guix-warning-port)
                     (ngettext s p n %gettext-domain)
                     (program-name) (program-name) prefix
                     args (... ...))))))))

(define-diagnostic warning "warning: ") ; emit a warning
(define-diagnostic info "")

(define-diagnostic report-error "error: ")
(define-syntax-rule (leave args ...)
  "Emit an error message and exit."
  (begin
    (report-error args ...)
    (exit 1)))

(define (print-unbound-variable-error port key args default-printer)
  ;; Print unbound variable errors more nicely, and in the right language.
  (match args
    ((proc message (variable) _ ...)
     ;; We can always omit PROC because when it's useful (i.e., different from
     ;; "module-lookup"), it gets displayed before.
     (format port (G_ "~a: unbound variable") variable))
    (_
     (default-printer))))

(set-exception-printer! 'unbound-variable print-unbound-variable-error)

(define (make-user-module modules)
  "Return a new user module with the additional MODULES loaded."
  ;; Module in which the machine description file is loaded.
  (let ((module (make-fresh-user-module)))
    (for-each (lambda (iface)
                (module-use! module (resolve-interface iface)))
              modules)
    module))

(define* (load* file user-module
                #:key (on-error 'nothing-special))
  "Load the user provided Scheme source code FILE."
  (define (frame-with-source frame)
    ;; Walk from FRAME upwards until source location information is found.
    (let loop ((frame    frame)
               (previous frame))
      (if (not frame)
          previous
          (if (frame-source frame)
              frame
              (loop (frame-previous frame) frame)))))

  (define (error-string frame args)
    (call-with-output-string
      (lambda (port)
        (apply display-error frame port (cdr args)))))

  (define tag
    (make-prompt-tag "user-code"))

  (catch #t
    (lambda ()
      ;; XXX: Force a recompilation to avoid ABI issues.
      ;;
      ;; In 2.2.3, the bogus answer to <https://bugs.gnu.org/29226> was to
      ;; ignore all available .go, not just those from ~/.cache, which in turn
      ;; meant that we had to rebuild *everything*.  Since this is too costly,
      ;; we have to turn off '%fresh-auto-compile' with that version, so to
      ;; avoid ABI breakage in the user's config file, we explicitly compile
      ;; it (the problem remains if the user's config is spread on several
      ;; modules.)  See <https://bugs.gnu.org/29881>.
      (unless (string=? (version) "2.2.3")
        (set! %fresh-auto-compile #t))

      (set! %load-should-auto-compile #t)

      (save-module-excursion
       (lambda ()
         (set-current-module user-module)

         ;; Hide the "auto-compiling" messages.
         (parameterize ((current-warning-port (%make-void-port "w")))
           (call-with-prompt tag
             (lambda ()
               (when (string=? (version) "2.2.3")
                 (catch 'system-error
                   (lambda ()
                     (compile-file file #:env user-module))
                   (const #f)))              ;EACCES maybe, let's interpret it

               ;; Give 'load' an absolute file name so that it doesn't try to
               ;; search for FILE in %LOAD-PATH.  Note: use 'load', not
               ;; 'primitive-load', so that FILE is compiled, which then allows us
               ;; to provide better error reporting with source line numbers.
               (load (canonicalize-path file)))
             (const #f))))))
    (lambda _
      ;; XXX: Errors are reported from the pre-unwind handler below, but
      ;; calling 'exit' from there has no effect, so we call it here.
      (exit 1))
    (rec (handle-error . args)
         ;; Capture the stack up to this procedure call, excluded, and pass
         ;; the faulty stack frame to 'report-load-error'.
         (let* ((stack (make-stack #t handle-error tag))
                (depth (stack-length stack))
                (last  (and (> depth 0) (stack-ref stack 0)))
                (frame (frame-with-source
                        (if (> depth 1)
                            (stack-ref stack 1)   ;skip the 'throw' frame
                            last))))

           (report-load-error file args frame)

           (case on-error
             ((debug)
              (newline)
              (display (G_ "entering debugger; type ',bt' for a backtrace\n"))
              (start-repl #:debug (make-debug (stack->vector stack) 0
                                              (error-string frame args)
                                              #f)))
             ((backtrace)
              (newline (current-error-port))
              (display-backtrace stack (current-error-port)))
             (else
              #t))))))

(define (known-variable-definition variable)
  "Search among the currently loaded modules one that defines a variable named
VARIABLE and return it, or #f if none was found."
  (define (module<? m1 m2)
    (match (module-name m2)
      (('gnu _ ...) #t)
      (('guix _ ...)
       (match (module-name m1)
         (('gnu _ ...) #f)
         (_ #t)))
      (_ #f)))

  (let loop ((modules     (list (resolve-module '() #f #f #:ensure #f)))
             (suggestions '())
             (visited     (setq)))
    (match modules
      (()
       ;; Pick the "best" suggestion.
       (match (sort suggestions module<?)
         (() #f)
         ((first _ ...) first)))
      ((head tail ...)
       (if (set-contains? visited head)
           (loop tail suggestions visited)
           (let ((visited (set-insert head visited))
                 (next    (append tail
                                  (hash-map->list (lambda (name module)
                                                    module)
                                                  (module-submodules head)))))
             (match (module-local-variable head variable)
               (#f (loop next suggestions visited))
               (_
                (match (module-name head)
                  (('gnu _ ...) head)             ;must be that one
                  (_ (loop next (cons head suggestions) visited)))))))))))

(define* (display-hint message #:optional (port (current-error-port)))
  "Display MESSAGE, a l10n message possibly containing Texinfo markup, to
PORT."
  (format port (G_ "hint: ~a~%")
          ;; XXX: We should arrange so that the initial indent is wider.
          (parameterize ((%text-width (max 15
                                           (- (terminal-columns) 5))))
            (texi->plain-text message))))

(define* (report-load-error file args #:optional frame)
  "Report the failure to load FILE, a user-provided Scheme file.
ARGS is the list of arguments received by the 'throw' handler."
  (match args
    (('system-error . rest)
     (let ((err (system-error-errno args)))
       (report-error (G_ "failed to load '~a': ~a~%") file (strerror err))))
    (('read-error "scm_i_lreadparen" message _ ...)
     ;; Guile's missing-paren messages are obscure so we make them more
     ;; intelligible here.
     (if (string-suffix? "end of file" message)
         (let ((location (string-drop-right message
                                            (string-length "end of file"))))
           (format (current-error-port) (G_ "~amissing closing parenthesis~%")
                   location))
         (apply throw args)))
    (('syntax-error proc message properties form . rest)
     (let ((loc (source-properties->location properties)))
       (format (current-error-port) (G_ "~a: error: ~a~%")
               (location->string loc) message)))
    (('unbound-variable proc message (variable) _ ...)
     (match args
       ((key . args)
        (print-exception (current-error-port) frame key args)))
     (match (known-variable-definition variable)
       (#f
        (display-hint (G_ "Did you forget a @code{use-modules} form?")))
       (module
        (display-hint (format #f (G_ "Did you forget @code{(use-modules ~a)}?")
                              (module-name module))))))
    (('srfi-34 obj)
     (if (message-condition? obj)
         (if (error-location? obj)
             (format (current-error-port)
                     (G_ "~a: error: ~a~%")
                     (location->string (error-location obj))
                     (gettext (condition-message obj)
                              %gettext-domain))
             (report-error (G_ "~a~%")
                           (gettext (condition-message obj)
                                    %gettext-domain)))
         (report-error (G_ "exception thrown: ~s~%") obj))
     (when (fix-hint? obj)
       (display-hint (condition-fix-hint obj))))
    ((error args ...)
     (report-error (G_ "failed to load '~a':~%") file)
     (apply display-error frame (current-error-port) args))))

(define (warn-about-load-error file args)         ;FIXME: factorize with ↑
  "Report the failure to load FILE, a user-provided Scheme file, without
exiting.  ARGS is the list of arguments received by the 'throw' handler."
  (match args
    (('system-error . rest)
     (let ((err (system-error-errno args)))
       (warning (G_ "failed to load '~a': ~a~%") file (strerror err))))
    (('syntax-error proc message properties form . rest)
     (let ((loc (source-properties->location properties)))
       (format (current-error-port) (G_ "~a: warning: ~a~%")
               (location->string loc) message)))
    (('srfi-34 obj)
     (if (message-condition? obj)
         (warning (G_ "failed to load '~a': ~a~%")
                  file
                  (gettext (condition-message obj) %gettext-domain))
         (warning (G_ "failed to load '~a': exception thrown: ~s~%")
                  file obj)))
    ((error args ...)
     (warning (G_ "failed to load '~a':~%") file)
     (apply display-error #f (current-error-port) args))))

(define (install-locale)
  "Install the current locale settings."
  (catch 'system-error
    (lambda _
      (setlocale LC_ALL ""))
    (lambda args
      (warning (G_ "failed to install locale: ~a~%")
               (strerror (system-error-errno args))))))

(define (initialize-guix)
  "Perform the usual initialization for stand-alone Guix commands."
  ;; By default don't annoy users with deprecation warnings.  In practice,
  ;; 'define-deprecated' in (ice-9 deprecated) arranges so that those warnings
  ;; are emitted at expansion-time only, but there are cases where they could
  ;; slip through, for instance when interpreting code.
  (unless (getenv "GUILE_WARN_DEPRECATED")
    (debug-disable 'warn-deprecated))

  (install-locale)
  (textdomain %gettext-domain)

  ;; Ignore SIGPIPE.  If the daemon closes the connection, we prefer to be
  ;; notified via an EPIPE later.
  (sigaction SIGPIPE SIG_IGN)

  (setvbuf (current-output-port) _IOLBF)
  (setvbuf (current-error-port) _IOLBF))

(define* (show-version-and-exit #:optional (command (car (command-line))))
  "Display version information for COMMAND and `(exit 0)'."
  (simple-format #t "~a (~a) ~a~%"
                 command %guix-package-name %guix-version)
  (format #t "Copyright ~a 2018 ~a"
          ;; TRANSLATORS: Translate "(C)" to the copyright symbol
          ;; (C-in-a-circle), if this symbol is available in the user's
          ;; locale.  Otherwise, do not translate "(C)"; leave it as-is.  */
          (G_ "(C)")
          (G_ "the Guix authors\n"))
  (display (G_"\
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
"))
  (exit 0))

(define (show-bug-report-information)
  ;; TRANSLATORS: The placeholder indicates the bug-reporting address for this
  ;; package.  Please add another line saying "Report translation bugs to
  ;; ...\n" with the address for translation bugs (typically your translation
  ;; team's web or email address).
  (format #t (G_ "
Report bugs to: ~a.") %guix-bug-report-address)
  (format #t (G_ "
~a home page: <~a>") %guix-package-name %guix-home-page-url)
  (display (G_ "
General help using GNU software: <http://www.gnu.org/gethelp/>"))
  (newline))

(define (augmented-system-error-handler file)
  "Return a 'system-error' handler that mentions FILE in its message."
  (lambda (key proc fmt args errno)
    ;; Augment the FMT and ARGS with information about TARGET (this
    ;; information is missing as of Guile 2.0.11, making the exception
    ;; uninformative.)
    (apply throw key proc "~A: ~S"
           (list (strerror (car errno)) file)
           (list errno))))

(define-syntax-rule (error-reporting-wrapper proc (args ...) file)
  "Wrap PROC such that its 'system-error' exceptions are augmented to mention
FILE."
  (let ((real-proc (@ (guile) proc)))
    (lambda (args ...)
      (catch 'system-error
        (lambda ()
          (real-proc args ...))
        (augmented-system-error-handler file)))))

(set! symlink
  ;; We 'set!' the global binding because (gnu build ...) modules and similar
  ;; typically don't use (guix ui).
  (error-reporting-wrapper symlink (source target) target))

(set! copy-file
  ;; Note: here we use 'set!', not #:replace, because UIs typically use
  ;; 'copy-recursively', which doesn't use (guix ui).
  (error-reporting-wrapper copy-file (source target) target))

(set! canonicalize-path
  (error-reporting-wrapper canonicalize-path (file) file))


(define (make-regexp* regexp . flags)
  "Like 'make-regexp' but error out if REGEXP is invalid, reporting the error
nicely."
  (catch 'regular-expression-syntax
    (lambda ()
      (apply make-regexp regexp flags))
    (lambda (key proc message . rest)
      (leave (G_ "'~a' is not a valid regular expression: ~a~%")
             regexp message))))

(define (string->number* str)
  "Like `string->number', but error out with an error message on failure."
  (or (string->number str)
      (leave (G_ "~a: invalid number~%") str)))

(define (size->number str)
  "Convert STR, a storage measurement representation such as \"1024\" or
\"1MiB\", to a number of bytes.  Raise an error if STR could not be
interpreted."
  (define unit-pos
    (string-rindex str char-set:digit))

  (define unit
    (and unit-pos (substring str (+ 1 unit-pos))))

  (let* ((numstr (if unit-pos
                     (substring str 0 (+ 1 unit-pos))
                     str))
         (num    (string->number numstr)))
    (unless num
      (leave (G_ "invalid number: ~a~%") numstr))

    ((compose inexact->exact round)
     (* num
        (match unit
          ((or "KiB" "K" "k") (expt 2 10))
          ((or "MiB" "M")     (expt 2 20))
          ((or "GiB" "G")     (expt 2 30))
          ((or "TiB" "T")     (expt 2 40))
          ((or "PiB" "P")     (expt 2 50))
          ((or "EiB" "E")     (expt 2 60))
          ((or "ZiB" "Z")     (expt 2 70))
          ((or "YiB" "Y")     (expt 2 80))
          ("kB"  (expt 10 3))
          ("MB"  (expt 10 6))
          ("GB"  (expt 10 9))
          ("TB"  (expt 10 12))
          ("PB"  (expt 10 15))
          ("EB"  (expt 10 18))
          ("ZB"  (expt 10 21))
          ("YB"  (expt 10 24))
          (""    1)
          (x
           (leave (G_ "unknown unit: ~a~%") unit)))))))

(define (display-collision-resolution-hint collision)
  "Display hints on how to resolve COLLISION, a &profile-collistion-error."
  (define (top-most-entry entry)
    (let loop ((entry entry))
      (match (force (manifest-entry-parent entry))
        (#f entry)
        (parent (loop parent)))))

  (let* ((first  (profile-collision-error-entry collision))
         (second (profile-collision-error-conflict collision))
         (name1  (manifest-entry-name (top-most-entry first)))
         (name2  (manifest-entry-name (top-most-entry second))))
    (if (string=? name1 name2)
        (display-hint (format #f (G_ "You cannot have two different versions
or variants of @code{~a} in the same profile.")
                              name1))
        (display-hint (format #f (G_ "Try upgrading both @code{~a} and @code{~a},
or remove one of them from the profile.")
                              name1 name2)))))

(define (call-with-error-handling thunk)
  "Call THUNK within a user-friendly error handler."
  (define (port-filename* port)
    ;; 'port-filename' returns #f for non-file ports, but it raises an
    ;; exception for file ports that are closed.  Work around that.
    (and (not (port-closed? port))
         (port-filename port)))

  (guard (c ((package-input-error? c)
             (let* ((package  (package-error-package c))
                    (input    (package-error-invalid-input c))
                    (location (package-location package))
                    (file     (location-file location))
                    (line     (location-line location))
                    (column   (location-column location)))
               (leave (G_ "~a:~a:~a: package `~a' has an invalid input: ~s~%")
                      file line column
                      (package-full-name package) input)))
            ((package-cross-build-system-error? c)
             (let* ((package (package-error-package c))
                    (loc     (package-location package))
                    (system  (package-build-system package)))
               (leave (G_ "~a: ~a: build system `~a' does not support cross builds~%")
                      (location->string loc)
                      (package-full-name package)
                      (build-system-name system))))
            ((gexp-input-error? c)
             (let ((input (package-error-invalid-input c)))
               (leave (G_ "~s: invalid G-expression input~%")
                      (gexp-error-invalid-input c))))
            ((profile-not-found-error? c)
             (leave (G_ "profile '~a' does not exist~%")
                    (profile-error-profile c)))
            ((missing-generation-error? c)
             (leave (G_ "generation ~a of profile '~a' does not exist~%")
                    (missing-generation-error-generation c)
                    (profile-error-profile c)))
            ((profile-collision-error? c)
             (let ((entry    (profile-collision-error-entry c))
                   (conflict (profile-collision-error-conflict c)))
               (define (report-parent-entries entry)
                 (let ((parent (force (manifest-entry-parent entry))))
                   (when (manifest-entry? parent)
                     (report-error (G_ "   ... propagated from ~a@~a~%")
                                   (manifest-entry-name parent)
                                   (manifest-entry-version parent))
                     (report-parent-entries parent))))

               (define (manifest-entry-output* entry)
                 (match (manifest-entry-output entry)
                   ("out"   "")
                   (output (string-append ":" output))))

               (report-error (G_ "profile contains conflicting entries for ~a~a~%")
                             (manifest-entry-name entry)
                             (manifest-entry-output* entry))
               (report-error (G_ "  first entry: ~a@~a~a ~a~%")
                             (manifest-entry-name entry)
                             (manifest-entry-version entry)
                             (manifest-entry-output* entry)
                             (manifest-entry-item entry))
               (report-parent-entries entry)
               (report-error (G_ "  second entry: ~a@~a~a ~a~%")
                             (manifest-entry-name conflict)
                             (manifest-entry-version conflict)
                             (manifest-entry-output* conflict)
                             (manifest-entry-item conflict))
               (report-parent-entries conflict)
               (display-collision-resolution-hint c)
               (exit 1)))
            ((nar-error? c)
             (let ((file (nar-error-file c))
                   (port (nar-error-port c)))
               (if file
                   (leave (G_ "corrupt input while restoring '~a' from ~s~%")
                          file (or (port-filename* port) port))
                   (leave (G_ "corrupt input while restoring archive from ~s~%")
                          (or (port-filename* port) port)))))
            ((nix-connection-error? c)
             (leave (G_ "failed to connect to `~a': ~a~%")
                    (nix-connection-error-file c)
                    (strerror (nix-connection-error-code c))))
            ((nix-protocol-error? c)
             ;; FIXME: Server-provided error messages aren't i18n'd.
             (leave (G_ "build failed: ~a~%")
                    (nix-protocol-error-message c)))
            ((derivation-missing-output-error? c)
             (leave (G_ "reference to invalid output '~a' of derivation '~a'~%")
                    (derivation-missing-output c)
                    (derivation-file-name (derivation-error-derivation c))))
            ((file-search-error? c)
             (leave (G_ "file '~a' could not be found in these \
directories:~{ ~a~}~%")
                    (file-search-error-file-name c)
                    (file-search-error-search-path c)))
            ((and (error-location? c) (message-condition? c))
             (format (current-error-port)
                     (G_ "~a: error: ~a~%")
                     (location->string (error-location c))
                     (gettext (condition-message c) %gettext-domain))
             (when (fix-hint? c)
               (display-hint (condition-fix-hint c)))
             (exit 1))
            ((and (message-condition? c) (fix-hint? c))
             (format (current-error-port) "~a: error: ~a~%"
                     (program-name)
                     (gettext (condition-message c) %gettext-domain))
             (display-hint (condition-fix-hint c))
             (exit 1))
            ((message-condition? c)
             ;; Normally '&message' error conditions have an i18n'd message.
             (leave (G_ "~a~%")
                    (gettext (condition-message c) %gettext-domain))))
    ;; Catch EPIPE and the likes.
    (catch 'system-error
      thunk
      (lambda (key proc format-string format-args . rest)
        (leave (G_ "~a: ~a~%") proc
               (apply format #f format-string format-args))))))

(define-syntax-rule (leave-on-EPIPE exp ...)
  "Run EXP... in a context when EPIPE errors are caught and lead to 'exit'
with successful exit code.  This is useful when writing to the standard output
may lead to EPIPE, because the standard output is piped through 'head' or
similar."
  (catch 'system-error
    (lambda ()
      exp ...)
    (lambda args
      ;; We really have to exit this brutally, otherwise Guile eventually
      ;; attempts to flush all the ports, leading to an uncaught EPIPE down
      ;; the path.
      (if (= EPIPE (system-error-errno args))
          (primitive-_exit 0)
          (apply throw args)))))

(define %guix-user-module
  ;; Module in which user expressions are evaluated.
  ;; Compute lazily to avoid circularity with (guix gexp).
  (delay
    (let ((module (make-module)))
      (beautify-user-module! module)
      ;; Use (guix gexp) so that one can use #~ & co.
      (module-use! module (resolve-interface '(guix gexp)))
      module)))

(define (read/eval str)
  "Read and evaluate STR, raising an error if something goes wrong."
  (let ((exp (catch #t
               (lambda ()
                 (call-with-input-string str read))
               (lambda args
                 (leave (G_ "failed to read expression ~s: ~s~%")
                        str args)))))
    (catch #t
      (lambda ()
        (eval exp (force %guix-user-module)))
      (lambda args
        (report-error (G_ "failed to evaluate expression '~a':~%") exp)
        (match args
          (('syntax-error proc message properties form . rest)
           (report-error (G_ "syntax error: ~a~%") message))
          (('srfi-34 obj)
           (if (message-condition? obj)
               (report-error (G_ "~a~%")
                             (gettext (condition-message obj)
                                      %gettext-domain))
               (report-error (G_ "exception thrown: ~s~%") obj)))
          ((error args ...)
           (apply display-error #f (current-error-port) args))
          (what? #f))
        (exit 1)))))

(define (read/eval-package-expression str)
  "Read and evaluate STR and return the package it refers to, or exit an
error."
  (match (read/eval str)
    ((? package? p) p)
    (x
     (leave (G_ "expression ~s does not evaluate to a package~%")
            str))))

(define (show-derivation-outputs derivation)
  "Show the output file names of DERIVATION."
  (format #t "~{~a~%~}"
          (map (match-lambda
                 ((out-name . out)
                  (derivation->output-path derivation out-name)))
               (derivation-outputs derivation))))

(define (check-available-space need)
  "Make sure at least NEED bytes are available in the store.  Otherwise emit a
warning."
  (let ((free (catch 'system-error
                (lambda ()
                  (free-disk-space (%store-prefix)))
                (const #f))))
    (when (and free (>= need free))
      (warning (G_ "at least ~,1h MB needed but only ~,1h MB available in ~a~%")
               (/ need 1e6) (/ free 1e6) (%store-prefix)))))

(define* (show-what-to-build store drv
                             #:key dry-run? (use-substitutes? #t)
                             (mode (build-mode normal)))
  "Show what will or would (depending on DRY-RUN?) be built in realizing the
derivations listed in DRV using MODE, a 'build-mode' value.  Return #t if
there's something to build, #f otherwise.  When USE-SUBSTITUTES?, check and
report what is prerequisites are available for download."
  (define substitutable-info
    ;; Call 'substitutation-oracle' upfront so we don't end up launching the
    ;; substituter many times.  This makes a big difference, especially when
    ;; DRV is a long list as is the case with 'guix environment'.
    (if use-substitutes?
        (substitution-oracle store drv #:mode mode)
        (const #f)))

  (define (built-or-substitutable? drv)
    (or (null? (derivation-outputs drv))
        (let ((out (derivation->output-path drv))) ;XXX: assume "out" exists
          (or (valid-path? store out)
              (substitutable-info out)))))

  (let*-values (((build download)
                 (fold2 (lambda (drv build download)
                          (let-values (((b d)
                                        (derivation-prerequisites-to-build
                                         store drv
                                         #:mode mode
                                         #:substitutable-info
                                         substitutable-info)))
                            (values (append b build)
                                    (append d download))))
                        '() '()
                        drv))
                ((build)                          ; add the DRV themselves
                 (delete-duplicates
                  (append (map derivation-file-name
                               (remove built-or-substitutable? drv))
                          (map derivation-input-path build))))
                ((download)                   ; add the references of DOWNLOAD
                 (if use-substitutes?
                     (delete-duplicates
                      (append download
                              (filter-map (lambda (item)
                                            (if (valid-path? store item)
                                                #f
                                                (substitutable-info item)))
                                          (append-map
                                           substitutable-references
                                           download))))
                     download)))
    (define installed-size
      (reduce + 0 (map substitutable-nar-size download)))

    (define download-size
      (/ (reduce + 0 (map substitutable-download-size download))
         1e6))

    (define display-download-size?
      ;; Sometimes narinfos lack information about the download size.  Only
      ;; display when we have information for all of DOWNLOAD.
      (not (any (compose zero? substitutable-download-size) download)))

    (if dry-run?
        (begin
          (format (current-error-port)
                  (N_ "~:[The following derivation would be built:~%~{   ~a~%~}~;~]"
                      "~:[The following derivations would be built:~%~{   ~a~%~}~;~]"
                      (length build))
                  (null? build) build)
          (if display-download-size?
              (format (current-error-port)
                      ;; TRANSLATORS: "MB" is for "megabyte"; it should be
                      ;; translated to the corresponding abbreviation.
                      (G_ "~:[~,1h MB would be downloaded:~%~{   ~a~%~}~;~]")
                      (null? download)
                      download-size
                      (map substitutable-path download))
              (format (current-error-port)
                      (N_ "~:[The following file would be downloaded:~%~{   ~a~%~}~;~]"
                          "~:[The following files would be downloaded:~%~{   ~a~%~}~;~]"
                          (length download))
                      (null? download)
                      (map substitutable-path download))))
        (begin
          (format (current-error-port)
                  (N_ "~:[The following derivation will be built:~%~{   ~a~%~}~;~]"
                      "~:[The following derivations will be built:~%~{   ~a~%~}~;~]"
                      (length build))
                  (null? build) build)
          (if display-download-size?
              (format (current-error-port)
                      ;; TRANSLATORS: "MB" is for "megabyte"; it should be
                      ;; translated to the corresponding abbreviation.
                      (G_ "~:[~,1h MB will be downloaded:~%~{   ~a~%~}~;~]")
                      (null? download)
                      download-size
                      (map substitutable-path download))
              (format (current-error-port)
                      (N_ "~:[The following file will be downloaded:~%~{   ~a~%~}~;~]"
                          "~:[The following files will be downloaded:~%~{   ~a~%~}~;~]"
                          (length download))
                      (null? download)
                      (map substitutable-path download)))))

    (check-available-space installed-size)

    (pair? build)))

(define show-what-to-build*
  (store-lift show-what-to-build))

(define (right-arrow port)
  "Return either a string containing the 'RIGHT ARROW' character, or an ASCII
replacement if PORT is not Unicode-capable."
  (let ((encoding (port-encoding port))
        (arrow "→"))
    (catch 'encoding-error
      (lambda ()
        (call-with-output-string
          (lambda (port)
            (set-port-encoding! port encoding)
            (set-port-conversion-strategy! port 'error)
            (display arrow port))))
      (lambda (key . args)
        "->"))))

(define* (show-manifest-transaction store manifest transaction
                                    #:key dry-run?)
  "Display what will/would be installed/removed from MANIFEST by TRANSACTION."
  (define (package-strings name version output item)
    (map (lambda (name version output item)
           (format #f "   ~a~:[:~a~;~*~]\t~a\t~a"
                   name
                   (equal? output "out") output version
                   (if (package? item)
                       (package-output store item output)
                       item)))
         name version output item))

  (define →                        ;an arrow that can be represented on stderr
    (right-arrow (current-error-port)))

  (define (upgrade-string name old-version new-version output item)
    (format #f "   ~a~:[:~a~;~*~]\t~a ~a ~a\t~a"
            name (equal? output "out") output
            old-version → new-version
            (if (package? item)
                (package-output store item output)
                item)))

  (let-values (((remove install upgrade downgrade)
                (manifest-transaction-effects manifest transaction)))
    (match remove
      ((($ <manifest-entry> name version output item) ..1)
       (let ((len    (length name))
             (remove (package-strings name version output item)))
         (if dry-run?
             (format (current-error-port)
                     (N_ "The following package would be removed:~%~{~a~%~}~%"
                         "The following packages would be removed:~%~{~a~%~}~%"
                         len)
                     remove)
             (format (current-error-port)
                     (N_ "The following package will be removed:~%~{~a~%~}~%"
                         "The following packages will be removed:~%~{~a~%~}~%"
                         len)
                     remove))))
      (x #f))
    (match downgrade
      (((($ <manifest-entry> name old-version)
         . ($ <manifest-entry> _ new-version output item)) ..1)
       (let ((len       (length name))
             (downgrade (map upgrade-string
                             name old-version new-version output item)))
         (if dry-run?
             (format (current-error-port)
                     (N_ "The following package would be downgraded:~%~{~a~%~}~%"
                         "The following packages would be downgraded:~%~{~a~%~}~%"
                         len)
                     downgrade)
             (format (current-error-port)
                     (N_ "The following package will be downgraded:~%~{~a~%~}~%"
                         "The following packages will be downgraded:~%~{~a~%~}~%"
                         len)
                     downgrade))))
      (x #f))
    (match upgrade
      (((($ <manifest-entry> name old-version)
         . ($ <manifest-entry> _ new-version output item)) ..1)
       (let ((len     (length name))
             (upgrade (map upgrade-string
                           name old-version new-version output item)))
         (if dry-run?
             (format (current-error-port)
                     (N_ "The following package would be upgraded:~%~{~a~%~}~%"
                         "The following packages would be upgraded:~%~{~a~%~}~%"
                         len)
                     upgrade)
             (format (current-error-port)
                     (N_ "The following package will be upgraded:~%~{~a~%~}~%"
                         "The following packages will be upgraded:~%~{~a~%~}~%"
                         len)
                     upgrade))))
      (x #f))
    (match install
      ((($ <manifest-entry> name version output item _) ..1)
       (let ((len     (length name))
             (install (package-strings name version output item)))
         (if dry-run?
             (format (current-error-port)
                     (N_ "The following package would be installed:~%~{~a~%~}~%"
                         "The following packages would be installed:~%~{~a~%~}~%"
                         len)
                     install)
             (format (current-error-port)
                     (N_ "The following package will be installed:~%~{~a~%~}~%"
                         "The following packages will be installed:~%~{~a~%~}~%"
                         len)
                     install))))
      (x #f))))

(define-syntax with-error-handling
  (syntax-rules ()
    "Run BODY within a user-friendly error condition handler."
    ((_ body ...)
     (call-with-error-handling
      (lambda ()
        body ...)))))

(define (location->string loc)
  "Return a human-friendly, GNU-standard representation of LOC."
  (match loc
    (#f (G_ "<unknown location>"))
    (($ <location> file line column)
     (format #f "~a:~a:~a" file line column))))

(define* (fill-paragraph str width #:optional (column 0))
  "Fill STR such that each line contains at most WIDTH characters, assuming
that the first character is at COLUMN.

When STR contains a single line break surrounded by other characters, it is
converted to a space; sequences of more than one line break are preserved."
  (define (maybe-break chr result)
    (match result
      ((column newlines chars)
       (case chr
         ((#\newline)
          `(,column ,(+ 1 newlines) ,chars))
         (else
          (let* ((spaces (if (and (pair? chars) (eqv? (car chars) #\.)) 2 1))
                 (chars  (case newlines
                           ((0) chars)
                           ((1)
                            (append (make-list spaces #\space) chars))
                           (else
                            (append (make-list newlines #\newline) chars))))
                 (column (case newlines
                           ((0) column)
                           ((1) (+ spaces column))
                           (else 0))))
            (let ((chars  (cons chr chars))
                  (column (+ 1 column)))
              (if (> column width)
                  (let*-values (((before after)
                                 (break (cut eqv? #\space <>) chars))
                                ((len)
                                 (length before)))
                    (if (<= len width)
                        `(,len
                          0
                          ,(if (null? after)
                               before
                               (append before
                                       (cons #\newline
                                             (drop-while (cut eqv? #\space <>)
                                                         after)))))
                        `(,column 0 ,chars)))     ; unbreakable
                  `(,column 0 ,chars)))))))))

  (match (string-fold maybe-break
                      `(,column 0 ())
                      str)
    ((column newlines chars)
     (list->string (reverse chars)))))

\f
;;;
;;; Packages.
;;;

(define %text-width
  (make-parameter (terminal-columns)))

(set! (@@ (texinfo plain-text) wrap*)
      ;; XXX: Monkey patch this private procedure to let 'package->recutils'
      ;; parameterize the fill of description field correctly.
      (lambda strings
        (let ((indent (fluid-ref (@@ (texinfo plain-text) *indent*))))
          (fill-string (string-concatenate strings)
                       #:line-width (%text-width) #:initial-indent indent
                       #:subsequent-indent indent))))

(define (texi->plain-text str)
  "Return a plain-text representation of texinfo fragment STR."
  ;; 'texi-fragment->stexi' uses a string port so make sure it's a
  ;; Unicode-capable one (see <http://bugs.gnu.org/11197>.)
  (with-fluids ((%default-port-encoding "UTF-8"))
    (stexi->plain-text (texi-fragment->stexi str))))

(define (package-field-string package field-accessor)
  "Return a plain-text representation of PACKAGE field."
  (and=> (field-accessor package)
         (compose texi->plain-text P_)))

(define (package-description-string package)
  "Return a plain-text representation of PACKAGE description field."
  (package-field-string package package-description))

(define (package-synopsis-string package)
  "Return a plain-text representation of PACKAGE synopsis field."
  (package-field-string package package-synopsis))

(define (string->recutils str)
  "Return a version of STR where newlines have been replaced by newlines
followed by \"+ \", which makes for a valid multi-line field value in the
`recutils' syntax."
  (list->string
   (string-fold-right (lambda (chr result)
                        (if (eqv? chr #\newline)
                            (cons* chr #\+ #\space result)
                            (cons chr result)))
                      '()
                      str)))

(define* (package->recutils p port #:optional (width (%text-width))
                            #:key (extra-fields '()))
  "Write to PORT a `recutils' record of package P, arranging to fit within
WIDTH columns.  EXTRA-FIELDS is a list of symbol/value pairs to emit."
  (define width*
    ;; The available number of columns once we've taken into account space for
    ;; the initial "+ " prefix.
    (if (> width 2) (- width 2) width))

  (define (dependencies->recutils packages)
    (let ((list (string-join (delete-duplicates
                              (map package-full-name
                                   (sort packages package<?))) " ")))
      (string->recutils
       (fill-paragraph list width*
                       (string-length "dependencies: ")))))

  (define (package<? p1 p2)
    (string<? (package-full-name p1) (package-full-name p2)))

  ;; Note: Don't i18n field names so that people can post-process it.
  (format port "name: ~a~%" (package-name p))
  (format port "version: ~a~%" (package-version p))
  (format port "outputs: ~a~%" (string-join (package-outputs p)))
  (format port "systems: ~a~%"
          (string-join (package-transitive-supported-systems p)))
  (format port "dependencies: ~a~%"
          (match (package-direct-inputs p)
            (((labels inputs . _) ...)
             (dependencies->recutils (filter package? inputs)))))
  (format port "location: ~a~%"
          (or (and=> (package-location p) location->string)
              (G_ "unknown")))

  ;; Note: Starting from version 1.6 or recutils, hyphens are not allowed in
  ;; field identifiers.
  (format port "homepage: ~a~%" (package-home-page p))

  (format port "license: ~a~%"
          (match (package-license p)
            (((? license? licenses) ...)
             (string-join (map license-name licenses)
                          ", "))
            ((? license? license)
             (license-name license))
            (x
             (G_ "unknown"))))
  (format port "synopsis: ~a~%"
          (string-map (match-lambda
                        (#\newline #\space)
                        (chr       chr))
                      (or (and=> (package-synopsis-string p) P_)
                          "")))
  (format port "~a~%"
          (string->recutils
           (string-trim-right
            (parameterize ((%text-width width*))
              (texi->plain-text
               (string-append "description: "
                              (or (and=> (package-description p) P_)
                                  ""))))
            #\newline)))
  (for-each (match-lambda
              ((field . value)
               (let ((field (symbol->string field)))
                 (format port "~a: ~a~%"
                         field
                         (fill-paragraph (object->string value) width*
                                         (string-length field))))))
            extra-fields)
  (newline port))

(define (relevance obj regexps metrics)
  "Compute a \"relevance score\" for OBJ as a function of its number of
matches of REGEXPS and accordingly to METRICS.  METRICS is list of
field/weight pairs, where FIELD is a procedure that returns a string
describing OBJ, and WEIGHT is a positive integer denoting the weight of this
field in the final score.

A score of zero means that OBJ does not match any of REGEXPS.  The higher the
score, the more relevant OBJ is to REGEXPS."
  (define (score str)
    (let ((counts (filter-map (lambda (regexp)
                                (match (regexp-exec regexp str)
                                  (#f #f)
                                  (m  (match:count m))))
                              regexps)))
      ;; Compute a score that's proportional to the number of regexps matched
      ;; and to the number of matches for each regexp.
      (* (length counts) (reduce + 0 counts))))

  (fold (lambda (metric relevance)
          (match metric
            ((field . weight)
             (match (field obj)
               (#f  relevance)
               (str (+ relevance
                       (* (score str) weight)))))))
        0
        metrics))

(define %package-metrics
  ;; Metrics used to compute the "relevance score" of a package against a set
  ;; of regexps.
  `((,package-name . 4)
    (,package-synopsis-string . 3)
    (,package-description-string . 2)
    (,(lambda (type)
        (match (and=> (package-location type) location-file)
          ((? string? file) (basename file ".scm"))
          (#f "")))
     . 1)))

(define (package-relevance package regexps)
  "Return a score denoting the relevance of PACKAGE for REGEXPS.  A score of
zero means that PACKAGE does not match any of REGEXPS."
  (relevance package regexps %package-metrics))

(define (string->generations str)
  "Return the list of generations matching a pattern in STR.  This function
accepts the following patterns: \"1\", \"1,2,3\", \"1..9\", \"1..\", \"..9\"."
  (define (maybe-integer)
    (let ((x (string->number str)))
      (and (integer? x)
           x)))

  (define (maybe-comma-separated-integers)
    (let ((lst (delete-duplicates
                (map string->number
                     (string-split str #\,)))))
      (and (every integer? lst)
           lst)))

  (cond ((maybe-integer)
         =>
         list)
        ((maybe-comma-separated-integers)
         =>
         identity)
        ((string-match "^([0-9]+)\\.\\.([0-9]+)$" str)
         =>
         (lambda (match)
           (let ((s (string->number (match:substring match 1)))
                 (e (string->number (match:substring match 2))))
             (and (every integer? (list s e))
                  (<= s e)
                  (iota (1+ (- e s)) s)))))
        ((string-match "^([0-9]+)\\.\\.$" str)
         =>
         (lambda (match)
           (let ((s (string->number (match:substring match 1))))
             (and (integer? s)
                  `(>= ,s)))))
        ((string-match "^\\.\\.([0-9]+)$" str)
         =>
         (lambda (match)
           (let ((e (string->number (match:substring match 1))))
             (and (integer? e)
                  `(<= ,e)))))
        (else #f)))

(define (string->duration str)
  "Return the duration matching a pattern in STR.  This function accepts the
following patterns: \"1d\", \"1w\", \"1m\"."
  (define (hours->duration hours match)
    (make-time time-duration 0
               (* 3600 hours (string->number (match:substring match 1)))))

  (cond ((string-match "^([0-9]+)s$" str)
         =>
         (lambda (match)
           (make-time time-duration 0
                      (string->number (match:substring match 1)))))
        ((string-match "^([0-9]+)h$" str)
         =>
         (lambda (match)
           (hours->duration 1 match)))
        ((string-match "^([0-9]+)d$" str)
         =>
         (lambda (match)
           (hours->duration 24 match)))
        ((string-match "^([0-9]+)w$" str)
         =>
         (lambda (match)
           (hours->duration (* 24 7) match)))
        ((string-match "^([0-9]+)m$" str)
         =>
         (lambda (match)
           (hours->duration (* 24 30) match)))
        (else #f)))

(define* (matching-generations str profile
                               #:key (duration-relation <=))
  "Return the list of available generations matching a pattern in STR.  See
'string->generations' and 'string->duration' for the list of valid patterns.
When STR is a duration pattern, return all the generations whose ctime has
DURATION-RELATION with the current time."
  (define (valid-generations lst)
    (define (valid-generation? n)
      (any (cut = n <>) (generation-numbers profile)))

    (fold-right (lambda (x acc)
                  (if (valid-generation? x)
                      (cons x acc)
                      acc))
                '()
                lst))

  (define (filter-generations generations)
    (match generations
      (() '())
      (('>= n)
       (drop-while (cut > n <>)
                   (generation-numbers profile)))
      (('<= n)
       (valid-generations (iota n 1)))
      ((lst ..1)
       (valid-generations lst))
      (x #f)))

  (define (filter-by-duration duration)
    (define (time-at-midnight time)
      ;; Return TIME at midnight by setting nanoseconds, seconds, minutes, and
      ;; hours to zeros.
      (let ((d (time-utc->date time)))
         (date->time-utc
          (make-date 0 0 0 0
                     (date-day d) (date-month d)
                     (date-year d) (date-zone-offset d)))))

    (define generation-ctime-alist
      (map (lambda (number)
             (cons number
                   (time-second
                    (time-at-midnight
                     (generation-time profile number)))))
           (generation-numbers profile)))

    (match duration
      (#f #f)
      (res
       (let ((s (time-second
                 (subtract-duration (time-at-midnight (current-time))
                                    duration))))
         (delete #f (map (lambda (x)
                           (and (duration-relation s (cdr x))
                                (first x)))
                         generation-ctime-alist))))))

  (cond ((string->generations str)
         =>
         filter-generations)
        ((string->duration str)
         =>
         filter-by-duration)
        (else #f)))

(define (display-generation profile number)
  "Display a one-line summary of generation NUMBER of PROFILE."
  (unless (zero? number)
    (let ((header (format #f (G_ "Generation ~a\t~a") number
                          (date->string
                           (time-utc->date
                            (generation-time profile number))
                           "~b ~d ~Y ~T")))
          (current (generation-number profile)))
      (if (= number current)
          ;; TRANSLATORS: The word "current" here is an adjective for
          ;; "Generation", as in "current generation".  Use the appropriate
          ;; gender where applicable.
          (format #t (G_ "~a\t(current)~%") header)
          (format #t "~a~%" header)))))

(define (display-profile-content-diff profile gen1 gen2)
  "Display the changed packages in PROFILE GEN2 compared to generation GEN2."

  (define (equal-entry? first second)
    (string= (manifest-entry-item first) (manifest-entry-item second)))

  (define (display-entry entry prefix)
    (match entry
      (($ <manifest-entry> name version output location _)
       (format #t " ~a ~a\t~a\t~a\t~a~%" prefix name version output location))))

  (define (list-entries number)
    (manifest-entries (profile-manifest (generation-file-name profile number))))

  (define (display-diff profile old new)
    (display-generation profile new)
    (let ((added (lset-difference
                  equal-entry? (list-entries new) (list-entries old)))
          (removed (lset-difference
                    equal-entry? (list-entries old) (list-entries new))))
      (for-each (cut display-entry <> "+") added)
      (for-each (cut display-entry <> "-") removed)
      (newline)))

  (display-diff profile gen1 gen2))

(define (display-profile-content profile number)
  "Display the packages in PROFILE, generation NUMBER, in a human-readable
way."
  (for-each (match-lambda
              (($ <manifest-entry> name version output location _)
               (format #t "  ~a\t~a\t~a\t~a~%"
                       name version output location)))

            ;; Show most recently installed packages last.
            (reverse
             (manifest-entries
              (profile-manifest (generation-file-name profile number))))))

(define (display-generation-change previous current)
  (format #t (G_ "switched from generation ~a to ~a~%") previous current))

(define (roll-back* store profile)
  "Like 'roll-back', but display what is happening."
  (call-with-values
      (lambda ()
        (roll-back store profile))
    display-generation-change))

(define (switch-to-generation* profile number)
  "Like 'switch-generation', but display what is happening."
  (let ((previous (switch-to-generation profile number)))
    (display-generation-change previous number)))

(define (delete-generation* store profile generation)
  "Like 'delete-generation', but display what is going on."
  (format #t (G_ "deleting ~a~%")
          (generation-file-name profile generation))
  (delete-generation store profile generation))

(define* (package-specification->name+version+output spec
                                                     #:optional (output "out"))
  "Parse package specification SPEC and return three value: the specified
package name, version number (or #f), and output name (or OUTPUT).  SPEC may
optionally contain a version number and an output name, as in these examples:

  guile
  guile@2.0.9
  guile:debug
  guile@2.0.9:debug
"
  (let*-values (((name sub-drv)
                 (match (string-rindex spec #\:)
                   (#f    (values spec output))
                   (colon (values (substring spec 0 colon)
                                  (substring spec (+ 1 colon))))))
                ((name version)
                 (package-name->name+version name)))
    (values name version sub-drv)))

\f
;;;
;;; Command-line option processing.
;;;

(define (show-guix-usage)
  (format (current-error-port)
          (G_ "Try `guix --help' for more information.~%"))
  (exit 1))

(define (command-files)
  "Return the list of source files that define Guix sub-commands."
  (define directory
    (and=> (search-path %load-path "guix.scm")
           (compose (cut string-append <> "/guix/scripts")
                    dirname)))

  (define dot-scm?
    (cut string-suffix? ".scm" <>))

  (if directory
      (scandir directory dot-scm?)
      '()))

(define (commands)
  "Return the list of Guix command names."
  (map (compose (cut string-drop-right <> 4)
                basename)
       (command-files)))

(define (show-guix-help)
  (define (internal? command)
    (member command '("substitute" "authenticate" "offload"
                      "perform-download")))

  (format #t (G_ "Usage: guix COMMAND ARGS...
Run COMMAND with ARGS.\n"))
  (newline)
  (format #t (G_ "COMMAND must be one of the sub-commands listed below:\n"))
  (newline)
  ;; TODO: Display a synopsis of each command.
  (format #t "~{   ~a~%~}" (sort (remove internal? (commands))
                                 string<?))
  (show-bug-report-information))

(define program-name
  ;; Name of the command-line program currently executing, or #f.
  (make-parameter #f))

(define (run-guix-command command . args)
  "Run COMMAND with the given ARGS.  Report an error when COMMAND is not
found."
  (define module
    (catch 'misc-error
      (lambda ()
        (resolve-interface `(guix scripts ,command)))
      (lambda -
        (format (current-error-port)
                (G_ "guix: ~a: command not found~%") command)
        (show-guix-usage))))

  (let ((command-main (module-ref module
                                  (symbol-append 'guix- command))))
    (parameterize ((program-name command))
      ;; Disable canonicalization so we don't don't stat unreasonably.
      (with-fluids ((%file-port-name-canonicalization #f))
        (dynamic-wind
          (const #f)
          (lambda ()
            (apply command-main args))
          (lambda ()
            ;; Abuse 'exit-hook' (which is normally meant to be used by the
            ;; REPL) to run things like profiling hooks upon completion.
            (run-hook exit-hook)))))))

(define (run-guix . args)
  "Run the 'guix' command defined by command line ARGS.
Unlike 'guix-main', this procedure assumes that locale, i18n support,
and signal handling has already been set up."
  (define option? (cut string-prefix? "-" <>))

  ;; The default %LOAD-EXTENSIONS includes the empty string, which doubles the
  ;; number of 'stat' calls per entry in %LOAD-PATH.  Shamelessly remove it.
  (set! %load-extensions '(".scm"))

  (match args
    (()
     (format (current-error-port)
             (G_ "guix: missing command name~%"))
     (show-guix-usage))
    ((or ("-h") ("--help"))
     (show-guix-help))
    (("--version")
     (show-version-and-exit "guix"))
    (((? option? o) args ...)
     (format (current-error-port)
             (G_ "guix: unrecognized option '~a'~%") o)
     (show-guix-usage))
    (("help" command)
     (apply run-guix-command (string->symbol command)
            '("--help")))
    (("help" args ...)
     (show-guix-help))
    ((command args ...)
     (apply run-guix-command
            (string->symbol command)
            args))))

(define guix-warning-port
  (make-parameter (current-warning-port)))

(define (guix-main arg0 . args)
  (initialize-guix)
  (apply run-guix args))

;;; ui.scm ends here