derivations: 'derivation' and related procedures return a single value.

* guix/derivations.scm (derivation->output-path,
  derivation->output-paths): New procedures.
  (derivation-path->output-path): Use 'derivation->output-path'.
  (derivation-path->output-paths): Use 'derivation->output-paths'.
  (derivation): Accept 'derivation?' objects as inputs.  Return a single
  value.
  (build-derivations): New procedure.
  (compiled-modules): Use 'derivation->output-paths'.
  (build-expression->derivation)[source-path]: Add case for when the
  input matches 'derivation?'.
  [prologue]: Accept 'derivation?' objects in INPUTS.
  [mod-dir, go-dir]: Use 'derivation->output-path'.
* guix/download.scm (url-fetch): Adjust to the single-value return.
* guix/packages.scm (package-output): Use 'derivation->output-path'.
* guix/scripts/build.scm (guix-build): When the argument is
  'derivation-path?', pass it through 'read-derivation'.
  Use 'derivation-file-name' to print out the .drv file names, and to
  register them.  Use 'derivation->output-path' instead of
  'derivation-path->output-path'.
* guix/scripts/package.scm (roll-back): Adjust to the single-value
  return.
  (guix-package): Use 'derivation->output-path'.
* guix/ui.scm (show-what-to-build): Adjust to deal with 'derivation?'
  objects instead of .drv file names.
* gnu/system/grub.scm (grub-configuration-file): Use
  'derivation->output-path' instead of 'derivation-path->output-path'.
* gnu/system/vm.scm (qemu-image, system-qemu-image): Likewise.
* tests/builders.scm, tests/derivations.scm, tests/packages.scm,
  tests/store.scm, tests/union.scm: Adjust to the new calling
  convention.
* doc/guix.texi (Defining Packages, The Store, Derivations): Adjust
  accordingly.

1 files changed, 13 insertions, 19 deletions

diff --git a/guix/download.scm b/guix/download.scm
index fa76615ef2..8b1d15f273 100644
--- a/guix/download.scm
+++ b/guix/download.scm
@@ -25,7 +25,6 @@
   #:use-module ((guix build download) #:renamer (symbol-prefix-proc 'build:))
   #:use-module (guix utils)
   #:use-module (srfi srfi-1)
-  #:use-module (srfi srfi-11)
   #:use-module (srfi srfi-26)
   #:export (%mirrors
             url-fetch
@@ -212,27 +211,22 @@ must be a list of symbol/URL-list pairs."
         ((url ...)
          (any https? url)))))
 
-  (let*-values (((gnutls-drv-path gnutls-drv)
-                 (if need-gnutls?
-                     (gnutls-derivation store system)
-                     (values #f #f)))
-                ((gnutls)
-                 (and gnutls-drv
-                      (derivation-output-path
-                       (assoc-ref (derivation-outputs gnutls-drv)
-                                  "out"))))
-                ((env-vars)
-                 (if gnutls
-                     (let ((dir (string-append gnutls "/share/guile/site")))
-                       ;; XXX: `GUILE_LOAD_COMPILED_PATH' is overridden
-                       ;; by `build-expression->derivation', so we can't
-                       ;; set it here.
-                       `(("GUILE_LOAD_PATH" . ,dir)))
-                     '())))
+  (let* ((gnutls-drv (if need-gnutls?
+                         (gnutls-derivation store system)
+                         (values #f #f)))
+         (gnutls     (and gnutls-drv
+                          (derivation->output-path gnutls-drv "out")))
+         (env-vars   (if gnutls
+                         (let ((dir (string-append gnutls "/share/guile/site")))
+                           ;; XXX: `GUILE_LOAD_COMPILED_PATH' is overridden
+                           ;; by `build-expression->derivation', so we can't
+                           ;; set it here.
+                           `(("GUILE_LOAD_PATH" . ,dir)))
+                         '())))
     (build-expression->derivation store (or name file-name) system
                                   builder
                                   (if gnutls-drv
-                                      `(("gnutls" ,gnutls-drv-path))
+                                      `(("gnutls" ,gnutls-drv))
                                       '())
                                   #:hash-algo hash-algo
                                   #:hash hash