refactor(_known_hosts_real,tar,upgradepkg): use "set" as positive flag

Author: akinomyoga

bash_completion

@@ -1970,8 +1970,14 @@ _known_hosts_real()
                 configfile=$OPTARG
                 ;;
             p) prefix=$OPTARG ;;
-            4) ipv4=1 ;;
-            6) ipv6=1 ;;
+            4)
+                # shellcheck disable=SC2209
+                ipv4=set
+                ;;
+            6)
+                # shellcheck disable=SC2209
+                ipv6=set
+                ;;
             *)
                 echo "bash_completion: $FUNCNAME: usage error" >&2
                 return 1

completions/tar

@@ -675,7 +675,8 @@ __tar_posix_prev_handle()
 
 _posix_tar()
 {
-    local long_opts short_opts basic_tar="" \
+    # shellcheck disable=SC2209
+    local long_opts short_opts basic_tar=set \
         long_arg_none="" long_arg_opt long_arg_req="" \
         short_arg_none short_arg_opt short_arg_req \
         tar_mode tar_mode_arg old_opt_progress=0 \
@@ -691,7 +692,6 @@ _posix_tar()
 
     _comp_initialize -s -- "$@" || return
 
-    basic_tar=yes
     tar_mode=none
 
     # relatively compatible modes are {c,t,x}

completions/upgradepkg

@@ -17,7 +17,8 @@ _upgradepkg()
         local nofiles="" IFS=$'\n'
         compopt -o filenames
         COMPREPLY=($(compgen -P "$prev%" -f -X "!*.@(t[bgxl]z)" -- "$cur"))
-        [[ ${COMPREPLY-} ]] || nofiles=1
+        # shellcheck disable=SC2209
+        [[ ${COMPREPLY-} ]] || nofiles=set
         COMPREPLY+=($(compgen -P "$prev%" -S '/' -d -- "$cur"))
         [[ $nofiles ]] && compopt -o nospace
         return