packages: Implement `package-cross-derivation'.

* guix/packages.scm (package-transitive-target-inputs,
  package-transitive-native-inputs): New procedures.
  (package-derivation): Parametrize `%current-target-system'.
  (package-cross-derivation): Implement.
* guix/utils.scm (%current-target-system): New variable.
* tests/packages.scm ("package-cross-derivation"): New test.
* doc/guix.texi (Defining Packages): Document
  `package-cross-derivation'.

1 files changed, 8 insertions, 1 deletions

diff --git a/tests/packages.scm b/tests/packages.scm
index 1dd7b91ae8..b439183eba 100644
--- a/tests/packages.scm
+++ b/tests/packages.scm
@@ -94,7 +94,7 @@
                    ("d" ,d) ("d/x" "something.drv"))
                  (pk 'x (package-transitive-inputs e))))))
 
-(test-skip (if (not %store) 4 0))
+(test-skip (if (not %store) 5 0))
 
 (test-assert "return values"
   (let-values (((drv-path drv)
@@ -196,6 +196,13 @@
            (equal? x (collect (package-derivation %store b)))
            (equal? x (collect (package-derivation %store c)))))))
 
+(test-assert "package-cross-derivation"
+  (let-values (((drv-path drv)
+                (package-cross-derivation %store (dummy-package "p")
+                                          "mips64el-linux-gnu")))
+    (and (derivation-path? drv-path)
+         (derivation? drv))))
+
 (unless (false-if-exception (getaddrinfo "www.gnu.org" "80" AI_NUMERICSERV))
   (test-skip 1))
 (test-assert "GNU Make, bootstrap"