Check for hardcoded versions

Fix issue 11

upgrade.sh

@@ -171,6 +171,20 @@ check_mrtest() {
 	err_exit "Run 'mrtest zap' first"
 }
 
+check_hardcoded_versions() {
+	local pattern='[=><]'
+	if ! grep -q "$pattern" /etc/apk/world; then
+		return
+	fi
+
+	warn "Found hardcoded versions /etc/apk/world:"
+	grep "$pattern" /etc/apk/world
+	warn "Remove them first, e.g. by editing /etc/apk/world and running"
+	warn "'apk fix'. This is for advanced users, if you don't know what"
+	warn "you are doing, better make a backup first and ask for help."
+	err_exit "Fix hardcoded versions first"
+}
+
 get_channel_current() {
 	# shellcheck disable=SC2155
 	local ret="$(grep '^VERSION="' /etc/os-release  | cut -d '"' -f 2)"
@@ -498,6 +512,7 @@ init_log "$0" "$@"
 check_is_pmos
 check_boot_size
 check_mrtest
+check_hardcoded_versions
 get_channels
 check_channels_valid
 check_channels_is_downgrade