pkgs/clerie-update-nixfiles: implement merge that properly overrides target with the full state of the update branch

pkgs/clerie-update-nixfiles/clerie-update-nixfiles.sh

@@ -6,6 +6,41 @@ xgit() {
 	git -c "user.name=Flake Update Bot" -c "user.email=flake-update-bot@clerie.de" -c "core.pager=cat" "$@"
 }
 
+xgit_merge_theirs() {
+  # base branch is the one currently checked out
+
+  # this is the branch we want to merge into the base branch
+  OTHER_BRANCH="$1"
+
+  # merge commit message
+  COMMIT_MESSAGE="$2"
+
+  # this branch gets used while merging
+  TEMP_BRANCH="tempbranch"
+
+  # create a merge commit between base branch and other branch, so it shows up correctly in git log
+  # we use `ours` so we make sure there are no merge conflicts
+  git merge -s ours "${OTHER_BRANCH}" -m "${COMMIT_MESSAGE}"
+
+  # save our newly created merge commit in a seperate branch
+  git branch "${TEMP_BRANCH}"
+
+  # export contents of other branch to current working directory
+  # this will change the last commit of our base branch too
+  git reset --hard "${OTHER_BRANCH}"
+
+  # return to our merge commit from the base branch
+  # but without touching the current working directory
+  git reset --soft "${TEMP_BRANCH}"
+
+  # Add the changes to our merge commit
+  git commit --amend --no-edit
+
+  # we are now on our base branch again
+  # so we can delete the temp branch
+  git branch -D "${TEMP_BRANCH}"
+}
+
 NOW="$(date --utc +%Y-%m-%d-%H-%M)"
 
 xgit status || xgit clone gitea@git.clerie.de:clerie/nixfiles.git .
@@ -43,7 +78,7 @@ xgit push --set-upstream origin "${UPDATE_BRANCH}"
 
 echo "[!] Merge ${UPDATE_BRANCH} into updated-inputs"
 xgit checkout updated-inputs
-xgit merge -s ort -X theirs "${UPDATE_BRANCH}" -m "Update from ${UPDATE_BRANCH}"
+xgit_merge_theirs "${UPDATE_BRANCH}" "Update from ${UPDATE_BRANCH}"
 
 echo "[!] Publish updated-inputs"
 xgit push origin updated-inputs