packages: Raise an error condition a cross builder is needed but unavailable.

* guix/packages.scm (&package-cross-build-system-error): New condition type.
  (package-cross-derivation): Raise &package-cross-build-system-error
  when the build system doesn't support cross builds.
* guix/ui.scm (call-with-error-handling): Add
  package-cross-build-system-error? case.
* tests/packages.scm ("package-cross-derivation, no cross builder"): New test.

1 files changed, 11 insertions, 1 deletions

diff --git a/guix/packages.scm b/guix/packages.scm
index 9d11b468fb..4f8d87e53a 100644
--- a/guix/packages.scm
+++ b/guix/packages.scm
@@ -83,7 +83,9 @@
             package-error-package
             &package-input-error
             package-input-error?
-            package-error-invalid-input))
+            package-error-invalid-input
+            &package-cross-build-system-error
+            package-cross-build-system-error?))
 
 ;;; Commentary:
 ;;;
@@ -234,6 +236,9 @@ corresponds to the arguments expected by `set-path-environment-variable'."
   package-input-error?
   (input package-error-invalid-input))
 
+(define-condition-type &package-cross-build-system-error &package-error
+  package-cross-build-system-error?)
+
 
 (define (package-full-name package)
   "Return the full name of PACKAGE--i.e., `NAME-VERSION'."
@@ -412,6 +417,11 @@ system identifying string)."
                   (= build-system-cross-builder builder)
                   args inputs propagated-inputs native-inputs self-native-input?
                   outputs)
+               (unless builder
+                 (raise (condition
+                         (&package-cross-build-system-error
+                          (package package)))))
+
                (let* ((inputs     (package-transitive-target-inputs package))
                       (input-drvs (map (cut expand-input
                                             store package <>