gexp: Allow use of high-level objects in #:references-graphs.

* guix/gexp.scm (lower-reference-graphs): New procedure.
  (gexp->derivation)[graphs-file-names]: New procedure.
  Use 'lower-reference-graphs', and augment #:inputs argument as a
  function of #:references-graphs.
* doc/guix.texi (G-Expressions): Adjust 'gexp->derivation' documentation
  accordingly.
* tests/gexp.scm ("gexp->derivation, store copy"): Remove reference to
  TWO in BUILD-DRV.  Use TWO directly in #:references-graphs argument.
  ("gexp->derivation #:references-graphs"): New test.
* gnu/system/vm.scm (qemu-image): Remove variable 'graph'; use INPUTS as
  the #:references-graphs argument to
  'expression->derivation-in-linux-vm'.

1 files changed, 16 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 1f192bf0a7..e0251f5ffd 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -2278,6 +2278,22 @@ search path to be copied in the store, compiled, and made available in
 the load path during the execution of @var{exp}---e.g., @code{((guix
 build utils) (guix build gnu-build-system))}.
 
+When @var{references-graphs} is true, it must be a list of tuples of one of the
+following forms:
+
+@example
+(@var{file-name} @var{package})
+(@var{file-name} @var{package} @var{output})
+(@var{file-name} @var{derivation})
+(@var{file-name} @var{derivation} @var{output})
+(@var{file-name} @var{store-item})
+@end example
+
+The right-hand-side of each element of @var{references-graphs} is automatically made
+an input of the build process of @var{exp}.  In the build environment, each
+@var{file-name} contains the reference graph of the corresponding item, in a simple
+text format.
+
 The other arguments are as for @code{derivation} (@pxref{Derivations}).
 @end deffn