remote: Build derivations appropriate for the remote's

* gnu/machine/ssh.scm (machine-ssh-configuration): Add 'system' field.
(managed-host-remote-eval): Pass 'system' field to 'remote-eval'.
(machine-check-building-for-appropriate-system): New variable.
(check-deployment-sanity): Add call to
'machine-check-building-for-appropriate-system'.
* doc/guix.texi (Invoking guix deploy): Describe new 'system' field.
* guix/ssh.scm (remote-system): New variable.
* guix/remote.scm (remote-eval): Use result of 'remote-system' when
lowering the G-Expression.
(remote-eval): Add 'system' keyword argument.
(trampoline): Return a <program-file> rather than a <scheme-file>.

2 files changed, 16 insertions, 5 deletions

diff --git a/guix/remote.scm b/guix/remote.scm
index 5fecd954e9..bcac64ea7a 100644
--- a/guix/remote.scm
+++ b/guix/remote.scm
@@ -24,6 +24,7 @@
   #:use-module (guix monads)
   #:use-module (guix modules)
   #:use-module (guix derivations)
+  #:use-module (guix utils)
   #:use-module (ssh popen)
   #:use-module (srfi srfi-1)
   #:use-module (ice-9 match)
@@ -71,7 +72,7 @@ prerequisites of EXP are already available on the host at SESSION."
   "Return a \"trampoline\" gexp that evaluates EXP and writes the evaluation
 result to the current output port using the (guix repl) protocol."
   (define program
-    (scheme-file "remote-exp.scm" exp))
+    (program-file "remote-exp.scm" exp))
 
   (with-imported-modules (source-module-closure '((guix repl)))
     #~(begin
@@ -89,6 +90,7 @@ result to the current output port using the (guix repl) protocol."
 (define* (remote-eval exp session
                       #:key
                       (build-locally? #t)
+                      (system (%current-system))
                       (module-path %load-path)
                       (socket-name "/var/guix/daemon-socket/socket"))
   "Evaluate EXP, a gexp, on the host at SESSION, an SSH session.  Ensure that
@@ -96,10 +98,12 @@ all the elements EXP refers to are built and deployed to SESSION beforehand.
 When BUILD-LOCALLY? is true, said dependencies are built locally and sent to
 the remote store afterwards; otherwise, dependencies are built directly on the
 remote store."
-  (mlet %store-monad ((lowered (lower-gexp (trampoline exp)
-                                           #:module-path %load-path))
-                      (remote -> (connect-to-remote-daemon session
-                                                           socket-name)))
+  (mlet* %store-monad ((lowered (lower-gexp (trampoline exp)
+                                            #:system system
+                                            #:guile-for-build #f
+                                            #:module-path %load-path))
+                       (remote -> (connect-to-remote-daemon session
+                                                            socket-name)))
     (define inputs
       (cons (lowered-gexp-guile lowered)
             (lowered-gexp-inputs lowered)))
diff --git a/guix/ssh.scm b/guix/ssh.scm
index ede00133c8..9b5ca68894 100644
--- a/guix/ssh.scm
+++ b/guix/ssh.scm
@@ -39,6 +39,7 @@
             remote-inferior
             remote-daemon-channel
             connect-to-remote-daemon
+            remote-system
             send-files
             retrieve-files
             retrieve-files*
@@ -282,6 +283,12 @@ be read.  When RECURSIVE? is true, the closure of FILES is exported."
                              ,(object->string
                                (object->string export))))))
 
+(define (remote-system session)
+  "Return the system type as expected by Nix, usually ARCHITECTURE-KERNEL, of
+the machine on the other end of SESSION."
+  (inferior-remote-eval '(begin (use-modules (guix utils)) (%current-system))
+                        session))
+
 (define* (send-files local files remote
                      #:key
                      recursive?