derivations: Add #:substitutable?, distinguished from #:local-build?.

Fixes <http://bugs.gnu.org/18747>.

* guix/derivations.scm (substitutable-derivation?): Rewrite to check for
  "allowSubstitutes".
  (derivation): Add #:substitutable? parameter.
  [user+system-env-vars]: Honor it.
  (build-expression->derivation): Add #:substitutable? and honor it.
* guix/gexp.scm (gexp->derivation): Likewise.
* tests/derivations.scm ("derivation-prerequisites-to-build and substitutes,
  non-substitutable build"): Use #:substitutable? instead of #:local-build?.
  ("substitutable-derivation?", "derivation-prerequisites-to-build and
  substitutes, local build"): New tests.
* guix/download.scm (url-fetch): Adjust comment.
* guix/git-download.scm (git-fetch): Likewise.
* guix/build-system/gnu.scm (gnu-build, gnu-cross-build): Use #:substitutable?
  instead of #:local-build?.
* doc/guix.texi (Derivations, G-Expressions): Adjust accordingly.

1 files changed, 37 insertions, 7 deletions

diff --git a/tests/derivations.scm b/tests/derivations.scm
index df5f07d117..f66ef5cdd7 100644
--- a/tests/derivations.scm
+++ b/tests/derivations.scm
@@ -188,10 +188,22 @@
 
 (test-assert "offloadable-derivation?"
   (and (offloadable-derivation? (derivation %store "foo" %bash '()))
+       (offloadable-derivation?               ;see <http://bugs.gnu.org/18747>
+        (derivation %store "foo" %bash '()
+                    #:substitutable? #f))
        (not (offloadable-derivation?
              (derivation %store "foo" %bash '()
                          #:local-build? #t)))))
 
+(test-assert "substitutable-derivation?"
+  (and (substitutable-derivation? (derivation %store "foo" %bash '()))
+       (substitutable-derivation?             ;see <http://bugs.gnu.org/18747>
+        (derivation %store "foo" %bash '()
+                    #:local-build? #f))
+       (not (substitutable-derivation?
+             (derivation %store "foo" %bash '()
+                         #:substitutable? #f)))))
+
 (test-assert "fixed-output-derivation?"
   (let* ((builder    (add-text-to-store %store "my-fixed-builder.sh"
                                         "echo -n hello > $out" '()))
@@ -614,14 +626,11 @@
              (null? download*)
              (null? build*))))))
 
-(test-assert "derivation-prerequisites-to-build and substitutes, local build"
+(test-assert "derivation-prerequisites-to-build and substitutes, non-substitutable build"
   (let* ((store  (open-connection))
-         (drv    (build-expression->derivation store "prereq-subst-local"
+         (drv    (build-expression->derivation store "prereq-no-subst"
                                                (random 1000)
-                                               ;; XXX: Adjust once
-                                               ;; <http://bugs.gnu.org/18747>
-                                               ;; is fixed.
-                                               #:local-build? #t))
+                                               #:substitutable? #f))
          (output (derivation->output-path drv)))
 
     ;; Make sure substitutes are usable.
@@ -631,13 +640,34 @@
       (let-values (((build download)
                     (derivation-prerequisites-to-build store drv)))
         ;; Despite being available as a substitute, DRV will be built locally
-        ;; due to #:local-build?.
+        ;; due to #:substitutable? #f.
         (and (null? download)
              (match build
                (((? derivation-input? input))
                 (string=? (derivation-input-path input)
                           (derivation-file-name drv)))))))))
 
+(test-assert "derivation-prerequisites-to-build and substitutes, local build"
+  (with-store store
+    (let* ((drv    (build-expression->derivation store "prereq-subst-local"
+                                                 (random 1000)
+                                                 #:local-build? #t))
+           (output (derivation->output-path drv)))
+
+      ;; Make sure substitutes are usable.
+      (set-build-options store #:use-substitutes? #t)
+
+      (with-derivation-narinfo drv
+        (let-values (((build download)
+                      (derivation-prerequisites-to-build store drv)))
+          ;; #:local-build? is not be synonymous with #:substitutable?, so we
+          ;; must be able to substitute DRV's output.
+          ;; See <http://bugs.gnu.org/18747>.
+          (and (null? build)
+               (match download
+                 (((? string? item))
+                  (string=? item (derivation->output-path drv))))))))))
+
 (test-assert "build-expression->derivation with expression returning #f"
   (let* ((builder  '(begin
                       (mkdir %output)