bug#44650: Do not suggest `guix pull --news' after first pull

["pelzflorian (Florian Pelz)" <pelzflorian@pelzflorian.de>]

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After doing a `guix pull` on the new VM image
<https://alpha.gnu.org/gnu/guix/guix-system-vm-image-1.2.0rc1.x86_64-linux.xz>,
the following is displayed:

> hint: Run `guix pull --news' to read all the news.
> 
> hint: After setting `PATH', run `hash guix' to make sure your shell refers to `/home/guest/.config/guix/current/bin/guix'.

The former `guix pull --news` is without effect (it is the very first
time I did a `guix pull`).  It is a no-op.  Users should not get the
suggestion to run `guix pull --news`.


Within (guix scripts pull)’ build-and-install procedure, the value of
(display-channel-news-headlines profile) is <unspecified>.

The attached patch changes it to return #f.  I have verified running
`guix pull --news' is not suggested anymore with it (although I have
not tested if news are still displayed).

It would perhaps be nicer if the news since version 1.2.0 were
displayed, but I do not know how to make it so.  I guess since the
original guix package must come from the guix package in (gnu packages
package-management), it is impossible to determine the version from
which news should be computed.

Regards,
Florian

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From 8da37dc91f2f82da5f1da0ed2b6f0c0602599e5c Mon Sep 17 00:00:00 2001
From: Florian Pelz <pelzflorian@pelzflorian.de>
Date: Sat, 14 Nov 2020 23:36:52 +0100
Subject: [PATCH] pull: Do not suggest running `guix pull --news' on the first
 run.

* guix/scripts/pull.scm (display-channel-news-headlines): If there
are no news to display, return false instead of <unspecified>.
---
 guix/scripts/pull.scm | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/guix/scripts/pull.scm b/guix/scripts/pull.scm
index bb1b560a22..38405fb79d 100644
--- a/guix/scripts/pull.scm
+++ b/guix/scripts/pull.scm
@@ -385,7 +385,7 @@ previous generation.  Return true if there are news to display."
     (and=> (relative-generation profile -1)
            (cut generation-file-name profile <>)))
 
-  (when previous
+  (if previous
     (let ((old-channels (profile-channels previous))
           (new-channels (profile-channels profile)))
       ;; Find the channels present in both PROFILE and PREVIOUS, and print
@@ -405,7 +405,8 @@ previous generation.  Return true if there are news to display."
                                                       #:concise? #t)))
                     channels))
 
-             (any ->bool more?))))))
+             (any ->bool more?))))
+    #f))
 
 (define (display-news profile)
   ;; Display profile news, with the understanding that this process represents
-- 
2.29.1