From c12431446666cd09ceceb0d9fa9f1c73113b4d9c Mon Sep 17 00:00:00 2001
From: Kévin Le Gouguec <kevin.legouguec@gmail.com>
Date: Sat, 23 Aug 2025 23:11:36 +0200
Subject: Change Emacs ELPA update script

Be cautiously optimistic: hope that the update process will work; stop
"generate dummy config & install everything from scratch" shenanigans.

(Do create a backup folder tho, just in case)

Also, compute patches for perusal.
---
 .local/bin/emacs-update-packages | 104 +++++++++++++++++++++++++++------------
 1 file changed, 72 insertions(+), 32 deletions(-)

diff --git a/.local/bin/emacs-update-packages b/.local/bin/emacs-update-packages
index 28d231d..2f162a5 100755
--- a/.local/bin/emacs-update-packages
+++ b/.local/bin/emacs-update-packages
@@ -1,47 +1,87 @@
 #!/bin/bash
 
+# Backup package-user-dir, update packages, compute diffs.
+#
+# Might be worth re-implementing as advice for package.el commands:
+# would avoid the "sacrificial" Emacs sessions…
+
 set -euo pipefail
-set -x
+test "${DEBUG:-}" && set -x
+
+BKPDIR=.elpa.$(date +%F-%T)
 
-backup-elpa ()
+read-packages ()
 {
-    (
-        cd ~/.emacs.d
-
-        # Make a timestamped snapshot for archival.
-        tar czf elpa.$(date +%F).tgz elpa
-
-        # Move directory out of Emacs's sight.  We could remove it
-        # altogether since we have the archived snapshot; keep it
-        # around for the very minor convenience gain.
-        rm -rf elpa.bkp
-        mv -T elpa elpa.bkp
-    )
+    local -n pkgarray=$1
+
+    local pkgel name version
+    for pkgel in elpa/*/*-pkg.el
+    do
+        # Extract NAME & VERSION out of elpa/NAME-VERSION/NAME-pkg.el.
+        pkgel=${pkgel#elpa/}
+
+        name=${pkgel}
+        name=${name##*/}
+        name=${name%-pkg.el}
+
+        version=${pkgel}
+        version=${version%/${name}-pkg.el}
+        version=${version#${name}-}
+
+        pkgarray[${name}]=${version}
+    done
 }
 
-gen-dotemacs ()
+enum-packages ()
 {
-    # --batch will not read my configuration.  Fall back to print-like
-    # functions, redirecting to 'external-debugging-output,
-    # redirecting stderr to stdout, and kill-emacs.
-    emacs 2>&1 \
-          --eval '(pp `(use-package package
-                        :custom
-                        (package-archives '\''(,@package-archives))
-                        (package-selected-packages '\''(,@package-selected-packages)))
-                      '\''external-debugging-output)' \
-          --funcall kill-emacs
+    IFS=$'\n' eval '
+        echo "${!OLDPACKAGES[*]}"
+        echo "${!NEWPACKAGES[*]}"
+    ' | sort -u
 }
 
+compare-packages ()
+{
+    local pkg oldv newv
 
-cd ~
+    while read pkg
+    do
+        oldv=${OLDPACKAGES[${pkg}]:-}
+        newv=${NEWPACKAGES[${pkg}]:-}
+
+        test "${oldv}" = "${newv}" &&
+            # No changes, skip.
+            continue
+
+        test "${oldv}" -a "${newv}" &&
+            # Make a patch for later review.
+            (
+                set +e
+                diff > ${BKPDIR}/update-${pkg}.patch \
+                    -ru ${BKPDIR}/${pkg}-${oldv} elpa/${pkg}-${newv}
+
+
+                diffstatus=$?
+                case ${diffstatus}
+                in
+                    0|1) exit 0 ;;
+                    *)   exit ${diffstatus} ;;
+                esac
+            )
+
+        echo -e "${pkg}\t${oldv:-[NEW]}\t${newv:-[REMOVED]}"
+    done
+}
 
-gen-dotemacs > .emacs.upgrade
+(
+    cd ~/.config/emacs
+    cp -a elpa ${BKPDIR}
 
-backup-elpa
-mv .emacs .emacs.bkp
+    declare -A OLDPACKAGES NEWPACKAGES
 
-cp .emacs.upgrade .emacs
-emacs --funcall package-install-selected-packages
+    read-packages OLDPACKAGES
+    emacs -f package-upgrade-all -f package-autoremove
+    read-packages NEWPACKAGES
 
-mv .emacs.bkp .emacs
+    enum-packages | compare-packages | column -ts$'\t'
+)
-- 
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