[bug#36872] [PATCH v2 1/2] remote: Build derivations appropriate for the remote's

[zerodaysfordays@sdf.lonestar.org (Jakob L. Kreuze)]

* guix/ssh.scm (remote-system): New variable.
* guix/remote.scm (remote-eval): Use result of 'remote-system' when
lowering the G-Expression.
(trampoline): Return a <program-file> rather than a <scheme-file>.
---
 guix/remote.scm | 13 ++++++++-----
 guix/ssh.scm    |  7 +++++++
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/guix/remote.scm b/guix/remote.scm
index 5fecd954e9..0a0bdaf30b 100644
--- a/guix/remote.scm
+++ b/guix/remote.scm
@@ -71,7 +71,7 @@ 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
@@ -96,10 +96,13 @@ 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 ((system -> (remote-system session))
+                       (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?
-- 
2.22.0