guix-package: Gracefully report non-existing outputs.

* guix-package.in (guix-package)[find-package](ensure-output): New
  procedure. Use it to validate SUB-DRV.

1 files changed, 10 insertions, 2 deletions

diff --git a/guix-package.in b/guix-package.in
index 053f8fbf83..58164c6e46 100644
--- a/guix-package.in
+++ b/guix-package.in
@@ -402,6 +402,14 @@ Install, remove, or upgrade PACKAGES in a single transaction.\n"))
     ;; sub-derivation name.
     (define request name)
 
+    (define (ensure-output p sub-drv)
+      (if (member sub-drv (package-outputs p))
+          p
+          (leave (_ "~a: error: package `~a' lacks output `~a'~%")
+                 (location->string (package-location p))
+                 (package-full-name p)
+                 sub-drv)))
+
     (let*-values (((name sub-drv)
                    (match (string-rindex name #\:)
                      (#f    (values name "out"))
@@ -411,7 +419,7 @@ Install, remove, or upgrade PACKAGES in a single transaction.\n"))
                    (package-name->name+version name)))
       (match (find-packages-by-name name version)
         ((p)
-         (list name (package-version p) sub-drv p))
+         (list name (package-version p) sub-drv (ensure-output p sub-drv)))
         ((p p* ...)
          (format (current-error-port)
                  (_ "warning: ambiguous package specification `~a'~%")
@@ -420,7 +428,7 @@ Install, remove, or upgrade PACKAGES in a single transaction.\n"))
                  (_ "warning: choosing ~a from ~a~%")
                  (package-full-name p)
                  (location->string (package-location p)))
-         (list name (package-version p) sub-drv p))
+         (list name (package-version p) sub-drv (ensure-output p sub-drv)))
         (()
          (leave (_ "~a: package not found~%") request)))))