services: home: Use pairs instead of lists.

* gnu/services/guix.scm: Use pairs instead of lists.
* doc/guix.texi: Update accordingly.
* gnu/tests/guix.scm: Update accordingly.

Change-Id: I0b8d3fa5b214add89bdb84a11fa20d1b319435f0

doc/guix.texi

@@ -39607,7 +39607,7 @@ the value is a home-environment configuration.
 
 (operating-system
   (services (append (list (service guix-home-service-type
-                                   `(("alice" ,my-home))))
+                                   `(("alice" . ,my-home))))
                     %base-services)))
 @end lisp
 
@@ -39616,7 +39616,7 @@ environments, as in this example:
 
 @lisp
 (simple-service 'my-extra-home home-service-type
-                `(("bob" ,my-extra-home))))
+                `(("bob" . ,my-extra-home))))
 @end lisp
 @end defvar
 

gnu/services/guix.scm

@@ -696,7 +696,7 @@ ca-certificates.crt file in the system profile."
 
 (define (guix-home-shepherd-service config)
   (map (match-lambda
-         ((user he)
+         (((? string? user) . (? home-environment? he))
           (shepherd-service
            (documentation "Activate Guix Home.")
            (requirement '(user-processes))
@@ -710,7 +710,9 @@ ca-certificates.crt file in the system profile."
                      (list (string-append "HOME=" (passwd:dir (getpw #$user)))
                            "GUIX_SYSTEM_IS_RUNNING_HOME_ACTIVATE=t")
                      #:group (group:name (getgrgid (passwd:gid (getpw #$user))))))
-           (stop #~(make-kill-destructor)))))
+           (stop #~(make-kill-destructor))))
+         (e (error "Invalid value for guix-home, it should be in a form of
+(\"user-name\" . home-environment), but the following value is provided:\n" e)))
        config))
 
 (define guix-home-service-type

gnu/tests/guix.scm

@@ -271,7 +271,7 @@ host	all	all	::1/128 	trust"))))))
 (define %guix-home-service-os
   (simple-operating-system
    (service guix-home-service-type
-            `(("alice" ,%guix-home-service-he)))))
+            `(("alice" . ,%guix-home-service-he)))))
 
 (define (run-guix-home-service-test)
   (define os