[bug#67598] [PATCH] gnu: services: guix: Allow gexps evaluating to a list of build-machines

[Saku Laesvuori]

* gnu/services/base.scm (guix-machines-files-installation): Handle
machines being a mixed list of build-machines and lists of
build-machines.
* doc/guix.texi: Document it.

Change-Id: Ie404562ca0b564413233c3a624046da831893dc3
---
This enables doing things like the DNS-SD example mentioned in '2.4.2
Using the Offload Facility' directly from the operating-system
declaration.

 doc/guix.texi         | 9 ++++++---
 gnu/services/base.scm | 8 +++++++-
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index 1fd2e21608..3e599742c3 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -19316,7 +19316,8 @@ Base Services
 @anchor{guix-configuration-build-machines}
 @item @code{build-machines} (default: @code{#f})
 This field must be either @code{#f} or a list of gexps evaluating to a
-@code{build-machine} record (@pxref{Daemon Offload Setup}).
+@code{build-machine} record or to a list of @code{build-machine} records
+(@pxref{Daemon Offload Setup}).
 
 When it is @code{#f}, the @file{/etc/guix/machines.scm} file is left
 untouched.  Otherwise, the list of of gexps is written to
@@ -19329,7 +19330,8 @@ Base Services
 (guix-configuration
   (build-machines
     (list #~(build-machine (name "foo.example.org") @dots{})
-          #~(build-machine (name "bar.example.org") @dots{}))))
+          #~(list (build-machine (name "bar.example.org") @dots{})
+                  (build-machine (name "foobaz.example.org") @dots{})))))
 @end lisp
 
 Additional build machines may be added @i{via} the @code{guix-extension}
@@ -19385,7 +19387,8 @@ Base Services
 A list of strings where each element is a substitute URL.
 
 @item @code{build-machines} (default: @code{'()})
-A list of gexps that evaluate to @code{build-machine} records
+A list of gexps that evaluate to @code{build-machine} records or to a list of
+@code{build-machine} records.
 (@pxref{Daemon Offload Setup}).
 
 Using this field, a service may add new build machines to receive builds
diff --git a/gnu/services/base.scm b/gnu/services/base.scm
index 82c6940780..beb710f95c 100644
--- a/gnu/services/base.scm
+++ b/gnu/services/base.scm
@@ -1765,7 +1765,13 @@ (define (guix-machines-files-installation machines)
             (mkdir-p (dirname machines-file)))
 
         ;; Installed the declared machines file.
-        (symlink #+(scheme-file "machines.scm" machines)
+        (symlink #+(scheme-file "machines.scm"
+                                `(apply append
+                                        (map (lambda (entry)
+                                               (if (list? entry)
+                                                 entry
+                                                 (list entry)))
+                                             ,machines)))
                  machines-file))))
 
 (define-record-type* <guix-configuration>

base-commit: cd46757c1a0f886848fbb6828c028dd2a2532767
-- 
2.41.0