cache: Work around 'time-monotonic' bug in Guile 2.2.2.

* guix/cache.scm (time-monotonic) [guile-2.2]: New variable.
* tests/cache.scm (time-monotonic) [guile-2.2]: Likewise.
* guix/build/download.scm (time-monotonic) [guile-2.2]: Adjust comment:
it's a 2.2.2 bug.

guix/build/download.scm

@@ -142,9 +142,8 @@ Otherwise return STORE-PATH."
 
 (cond-expand
   (guile-2.2
-   ;; Guile 2.2.0 to 2.2.2 included has a bug whereby 'time-monotonic' objects
-   ;; have seconds and nanoseconds swapped (fixed in Guile commit 886ac3e).
-   ;; Work around it.
+   ;; Guile 2.2.2 has a bug whereby 'time-monotonic' objects have seconds and
+   ;; nanoseconds swapped (fixed in Guile commit 886ac3e).  Work around it.
    (define time-monotonic time-tai))
   (else #t))
 

guix/cache.scm

@@ -33,6 +33,13 @@
 ;;;
 ;;; Code:
 
+(cond-expand
+  (guile-2.2
+   ;; Guile 2.2.2 has a bug whereby 'time-monotonic' objects have seconds and
+   ;; nanoseconds swapped (fixed in Guile commit 886ac3e).  Work around it.
+   (define time-monotonic time-tai))
+  (else #t))
+
 (define (obsolete? date now ttl)
   "Return #t if DATE is obsolete compared to NOW + TTL seconds."
   (time>? (subtract-duration now (make-time time-duration 0 ttl))

tests/cache.scm

@@ -24,6 +24,13 @@
   #:use-module ((guix utils) #:select (call-with-temporary-directory))
   #:use-module (ice-9 match))
 
+(cond-expand
+  (guile-2.2
+   ;; Guile 2.2.2 has a bug whereby 'time-monotonic' objects have seconds and
+   ;; nanoseconds swapped (fixed in Guile commit 886ac3e).  Work around it.
+   (define time-monotonic time-tai))
+  (else #t))
+
 (test-begin "cache")
 
 (test-equal "remove-expired-cache-entries"