file-systems: 'uuid' raises a syntax error for invalid UUIDs.

* gnu/system/file-systems.scm (uuid): Call 'syntax-violation' when
  'string->uuid' returns #f.
* tests/file-systems.scm ("uuid, syntax error"): New test.

gnu/system/file-systems.scm

@@ -153,8 +153,10 @@ UUID representation."
       ((_ str)
        (string? (syntax->datum #'str))
        ;; A literal string: do the conversion at expansion time.
-       (with-syntax ((bv (string->uuid (syntax->datum #'str))))
-         #''bv))
+       (let ((bv (string->uuid (syntax->datum #'str))))
+         (unless bv
+           (syntax-violation 'uuid "invalid UUID" s))
+         (datum->syntax #'str bv)))
       ((_ str)
        #'(string->uuid str)))))
 

tests/file-systems.scm

@@ -40,6 +40,16 @@
     (bytevector=? (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")
                   (string->uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb"))))
 
+(test-assert "uuid, syntax error"
+  (catch 'syntax-error
+    (lambda ()
+      (eval '(uuid "foobar") (current-module))
+      #f)
+    (lambda (key proc message location form . args)
+      (and (eq? proc 'uuid)
+           (string-contains message "invalid UUID")
+           (equal? form '(uuid "foobar"))))))
+
 (test-end)