From 0489ee1e567a8a7674fab9b27014b2c3f7383004 Mon Sep 17 00:00:00 2001
From: Kévin Le Gouguec <kevin.legouguec@gmail.com>
Date: Mon, 3 Nov 2025 07:48:38 +0100
Subject: Hide current elpa directory behind a symlink
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Simplifies rollbacks: revert symlink to previous directory.

Also,

* make directory names more intuitive: use $(date) for the _new_
directory, instead of the old one;
* write update patches to the new directory, instead of the old one;
* tee update summary to the new directory, so that it survives the
transient shell the update was run from.

Also, ask the augurs why 'test' has both -h and -L for symbolic links,

https://pubs.opengroup.org/onlinepubs/9799919799/utilities/test.html

and get no answer 🤷
---
 .local/bin/emacs-update-packages | 32 ++++++++++++++++++++------------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/.local/bin/emacs-update-packages b/.local/bin/emacs-update-packages
index 2f162a5..ecf5267 100755
--- a/.local/bin/emacs-update-packages
+++ b/.local/bin/emacs-update-packages
@@ -8,7 +8,15 @@
 set -euo pipefail
 test "${DEBUG:-}" && set -x
 
-BKPDIR=.elpa.$(date +%F-%T)
+cd ~/.config/emacs
+
+test -L elpa || {
+    echo >&2 "'elpa' directory must be a symlink."
+    exit 1
+}
+
+OLDELPADIR=$(readlink elpa)
+NEWELPADIR=.elpa.$(date +%F-%T)
 
 read-packages ()
 {
@@ -57,8 +65,8 @@ compare-packages ()
             # Make a patch for later review.
             (
                 set +e
-                diff > ${BKPDIR}/update-${pkg}.patch \
-                    -ru ${BKPDIR}/${pkg}-${oldv} elpa/${pkg}-${newv}
+                diff > ${NEWELPADIR}/update-${pkg}.patch \
+                    -ru ${OLDELPADIR}/${pkg}-${oldv} ${NEWELPADIR}/${pkg}-${newv}
 
 
                 diffstatus=$?
@@ -73,15 +81,15 @@ compare-packages ()
     done
 }
 
-(
-    cd ~/.config/emacs
-    cp -a elpa ${BKPDIR}
+cp -a ${OLDELPADIR} ${NEWELPADIR}
+
+declare -A OLDPACKAGES NEWPACKAGES
 
-    declare -A OLDPACKAGES NEWPACKAGES
+read-packages OLDPACKAGES
+ln -fsT ${NEWELPADIR} elpa
 
-    read-packages OLDPACKAGES
-    emacs -f package-upgrade-all -f package-autoremove
-    read-packages NEWPACKAGES
+emacs -f package-upgrade-all -f package-autoremove
+read-packages NEWPACKAGES
 
-    enum-packages | compare-packages | column -ts$'\t'
-)
+enum-packages | compare-packages | column -ts$'\t' |
+    tee ${NEWELPADIR}/update.sum
-- 
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