services: 'instantiate-missing-services' reaches fixed point.

Fixes a bug whereby services indirectly depended on would not be
automatically instantiated.

* gnu/services.scm (instantiate-missing-services): Loop back when the
length of ADJUSTED is greater than that of INSTANCES.
* tests/services.scm ("instantiate-missing-services, indirect"): New test.

1 files changed, 17 insertions, 7 deletions

diff --git a/gnu/services.scm b/gnu/services.scm
index 49cf01a4f8..f151bbaa9d 100644
--- a/gnu/services.scm
+++ b/gnu/services.scm
@@ -732,13 +732,23 @@ instantiated; other missing services lead to a
            instances
            (service-type-extensions (service-kind svc))))
 
-  (let ((instances (fold (lambda (service result)
-                           (vhash-consq (service-kind service) service
-                                        result))
-                         vlist-null services)))
-    (fold2 adjust-service-list
-           services instances
-           services)))
+  (let loop ((services services))
+    (define instances
+      (fold (lambda (service result)
+              (vhash-consq (service-kind service) service
+                           result))
+            vlist-null services))
+
+    (define adjusted
+      (fold2 adjust-service-list
+             services instances
+             services))
+
+    ;; If we instantiated services, they might in turn depend on missing
+    ;; services.  Loop until we've reached fixed point.
+    (if (= (length adjusted) (vlist-length instances))
+        adjusted
+        (loop adjusted))))
 
 (define* (fold-services services
                         #:key (target-type system-service-type))