derivations: Raise an error for references to non-existent outputs.

Fixes <http://bugs.gnu.org/19630>.
Reported by Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de>.

* guix/derivations.scm (&derivation-error,
  &derivation-missing-output-error): New error conditions.
  (derivation->output-path): Raise a '&derivation-missing-output-error'
  if OUTPUT is not an output of DRV.
* guix/ui.scm (call-with-error-handling): Add case for
  'derivation-missing-output-error?'.
  (show-what-to-build): Check whether (derivation-outputs drv) is
  empty.
* tests/packages.scm ("reference to non-existent output"): Add test.

1 files changed, 11 insertions, 0 deletions

diff --git a/tests/packages.scm b/tests/packages.scm
index ef34e76380..65e5cc3cdd 100644
--- a/tests/packages.scm
+++ b/tests/packages.scm
@@ -268,6 +268,17 @@
       (package-derivation %store p)
       #f)))
 
+(test-assert "reference to non-existent output"
+  ;; See <http://bugs.gnu.org/19630>.
+  (let* ((dep (dummy-package "dep"))
+         (p   (dummy-package "p"
+                (inputs `(("dep" ,dep "non-existent"))))))
+    (guard (c ((derivation-missing-output-error? c)
+               (and (string=? (derivation-missing-output c) "non-existent")
+                    (equal? (package-derivation %store dep)
+                            (derivation-error-derivation c)))))
+      (package-derivation %store p))))
+
 (test-assert "trivial"
   (let* ((p (package (inherit (dummy-package "trivial"))
               (build-system trivial-build-system)