refresh: Make --list-updaters fast if web.cvs.savannah.gnu.org is broken.

--list-updaters loops through all packages and all updaters to see whether they
match. The gnu-ftp updater used to use official-gnu-packages to fetch a list of
packages from web.cvs.savannah.gnu.org. official-gnu-packages only caches the
result if it succeeds; but does not cache upon a timout or 5xx status.
official-gnu-packages times out after a minute and is called for all 30k+
packages. refresh --list-updaters could therefore take 30000 minutes. Now
--list-updaters uses official-gnu-packages* (from lint.scm) that memoizes the
result also on failure, thereby limiting the time to 1 minute.

* guix/gnu-maintenance.scm: Add official-gnu-packages* from guix/lint.scm.
Call official-gnu-packages* from gnu-package?
* guix/lint.scm: Move official-gnu-packages* to guix/gnu-maintenance.scm

Change-Id: I5e2e094bfb1042b03db47e119ced0e94b49b417c
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Merges: #4949

guix/gnu-maintenance.scm

@@ -61,6 +61,7 @@
             gnu-package-download-url
 
             official-gnu-packages
+            official-gnu-packages*
             find-package
             gnu-package?
 
@@ -181,6 +182,13 @@ to fetch the list of GNU packages over HTTP."
          (close-port port)
          lst)))
 
+(define official-gnu-packages*
+  (mlambda ()
+    "A memoizing version of 'official-gnu-packages' that returns the empty
+list when something goes wrong, such as a networking issue."
+    (let ((gnus (false-if-exception (official-gnu-packages))))
+      (or gnus '()))))
+
 (define (find-package name)
   "Find GNU package called NAME and return it.  Return #f if it was not
 found."
@@ -189,7 +197,6 @@ found."
         (official-gnu-packages)))
 
 (define gnu-package?
-  (let ((official-gnu-packages (memoize official-gnu-packages)))
   (mlambdaq (package)
     "Return true if PACKAGE is a GNU package.  This procedure may access the
 network to check in GNU's database."
@@ -231,9 +238,9 @@ network to check in GNU's database."
                ((gnu) #t)
                ((non-gnu) #f)
                (else
-                  (and (member name (map gnu-package-name (official-gnu-packages)))
+                (and (member name (map gnu-package-name (official-gnu-packages*)))
                      #t)))))
-            (_ #f))))))
+          (_ #f)))))
 
 
 ;;;

guix/lint.scm

@@ -1237,13 +1237,6 @@ upstream status")
                       '()
                       str)))
 
-(define official-gnu-packages*
-  (mlambda ()
-    "A memoizing version of 'official-gnu-packages' that returns the empty
-list when something goes wrong, such as a networking issue."
-    (let ((gnus (false-if-exception (official-gnu-packages))))
-      (or gnus '()))))
-
 (define (check-gnu-synopsis+description package)
   "Make sure that, if PACKAGE is a GNU package, it uses the synopsis and
 descriptions maintained upstream."