refactor(completions/*): avoid [[ -v var ]] for localvar_inherit

When the assigned values are ensured to be non-empty strings, [[ -v
var ]] is converted to [[ $var ]].  Otherwise, another local variable
`has_var` is added to manage the assigned state, and [[ -v var ]] is
converted to [[ $has_var ]].  I here did not consider whether the
empty value of $var actually makes a sense or not.

Author: akinomyoga

completions/_adb

@@ -25,16 +25,16 @@ _comp_cmd_adb()
             ;;
     esac
 
-    local cmd i
-    unset -v cmd # workaround for localvar_inherit
+    local cmd has_cmd="" i
     for ((i = 1; i < cword; i++)); do
         if [[ ${words[i]} != -* && ${words[i - 1]} != -[sp] ]]; then
             cmd="${words[i]}"
+            has_cmd=yes
             break
         fi
     done
 
-    if [[ ! -v cmd ]]; then
+    if [[ ! $has_cmd ]]; then
         local tmp=()
         if [[ ! $cur || $cur == -* ]]; then
             tmp+=($(compgen -W '$(_parse_help "$1" help)' -- "$cur"))

completions/_chsh

@@ -8,14 +8,13 @@ _comp_cmd_chsh()
     local cur prev words cword comp_args
     _comp_initialize -- "$@" || return
 
-    local word chroot
-    unset -v chroot # workaround for localvar_inherit
+    local word chroot="" has_chroot=""
     for word in "${words[@]}"; do
-        if [[ -v chroot ]]; then
+        if [[ $has_chroot ]]; then
             chroot=$word
             break
         fi
-        [[ $word != -@(R|-root) ]] || chroot=
+        [[ $word != -@(R|-root) ]] || has_chroot=yes
     done
 
     case $prev in

completions/_op

@@ -30,28 +30,28 @@ _comp_cmd_op()
     local cur prev words cword split comp_args
     _comp_initialize -s -- "$@" || return
 
-    local command i
-    unset -v command # workaround for localvar_inherit
+    local command has_command="" i
     for ((i = 1; i < cword; i++)); do
         case ${words[i]} in
             --help | --version) return ;;
             -*) ;;
             *)
                 command=${words[i]}
+                has_command=yes
                 break
                 ;;
         esac
     done
 
-    if [[ ! -v command && $cur == -* ]]; then
+    if [[ ! $has_command && $cur == -* ]]; then
         COMPREPLY=($(compgen -W '$(_parse_usage "$1" --help)' -- "$cur"))
         [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
         return
     fi
 
-    [[ -v command ]] && _comp_cmd_op__command_options "$1" && return
+    [[ $has_command ]] && _comp_cmd_op__command_options "$1" && return
 
-    if [[ ! -v command || $command == "$prev" ]]; then
+    if [[ ! $has_command || $command == "$prev" ]]; then
         COMPREPLY=($(compgen -W '$(_op_commands "$1" ${command-})' -- "$cur"))
         [[ ${COMPREPLY-} ]] && return
     fi

completions/_udevadm

@@ -8,11 +8,11 @@ _comp_cmd_udevadm()
     local cur prev words cword split comp_args
     _comp_initialize -s -- "$@" || return
 
-    local i udevcmd
-    unset -v udevcmd # workaround for localvar_inherit
+    local i udevcmd has_udevcmd=""
     for ((i = 1; i < cword; i++)); do
         if [[ ${words[i]} != -* ]]; then
             udevcmd=${words[i]}
+            has_udevcmd=yes
             break
         fi
     done
@@ -54,7 +54,7 @@ _comp_cmd_udevadm()
 
     $split && return
 
-    if [[ ! -v udevcmd ]]; then
+    if [[ ! $has_udevcmd ]]; then
         case $cur in
             -*)
                 COMPREPLY=($(compgen -W '--help --version --debug' -- "$cur"))

completions/_yum

@@ -42,16 +42,15 @@ _comp_cmd_yum()
     local cur prev words cword split comp_args
     _comp_initialize -s -- "$@" || return
 
-    local special i
-    unset -v special # workaround for localvar_inherit
+    local special="" i
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
         if [[ ${words[i]} == @(install|update|upgrade|remove|erase|deplist|info) ]]; then
             special=${words[i]}
             break
         fi
     done
 
-    if [[ -v special ]]; then
+    if [[ $special ]]; then
         # TODO: install|update|upgrade should not match *src.rpm
         if [[ $cur == @(*/|[.~])* &&
             $special == @(deplist|install|update|upgrade) ]]; then

completions/apt-build

@@ -5,16 +5,15 @@ _apt_build()
     local cur prev words cword comp_args
     _comp_initialize -- "$@" || return
 
-    local special i
-    unset -v special # workaround for localvar_inherit
+    local special="" i
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
         if [[ ${words[i]} == @(install|remove|source|info|clean) ]]; then
             special=${words[i]}
             break
         fi
     done
 
-    if [[ -v special ]]; then
+    if [[ $special ]]; then
         case $special in
             install | source | info)
                 COMPREPLY=($(_comp_xfunc apt-cache packages))

completions/apt-cache

@@ -28,8 +28,7 @@ _apt_cache()
     local cur prev words cword comp_args
     _comp_initialize -- "$@" || return
 
-    local special ispecial
-    unset -v special # workaround for localvar_inherit
+    local special="" ispecial
     if [[ $cur != show ]]; then
         for ((ispecial = 1; ispecial < ${#words[@]} - 1; ispecial++)); do
             if [[ ${words[ispecial]} == @(add|depends|dotty|madison|policy|rdepends|show?(pkg|src|)) ]]; then
@@ -39,7 +38,7 @@ _apt_cache()
         done
     fi
 
-    if [[ -v special && $ispecial -lt $cword ]]; then
+    if [[ $special && $ispecial -lt $cword ]]; then
         case $special in
             add)
                 _filedir
@@ -85,7 +84,7 @@ _apt_cache()
             --full --all-versions --no-all-versions --generate --no-generate
             --names-only --all-names --recurse --installed --with-source --help
             --version --config-file --option' -- "$cur"))
-    elif [[ ! -v special ]]; then
+    elif [[ ! $special ]]; then
         COMPREPLY=($(compgen -W 'gencaches showpkg stats showsrc dump
             dumpavail unmet show search depends rdepends pkgnames dotty xvcg
             policy madison' -- "$cur"))

completions/apt-get

@@ -20,16 +20,15 @@ _apt_get()
     local cur prev words cword comp_args package
     _comp_initialize -n ':=' -- "$@" || return
 
-    local special i
-    unset -v special # workaround for localvar_inherit
+    local special="" i
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
         if [[ ${words[i]} == @(install|remove|auto?(-)remove|purge|source|build-dep|download|changelog) ]]; then
             special=${words[i]}
             break
         fi
     done
 
-    if [[ -v special ]]; then
+    if [[ $special ]]; then
         case $special in
             remove | auto?(-)remove | purge)
                 _comp_xfunc_apt_get_installed_packages

completions/apt-mark

@@ -5,16 +5,15 @@ _comp_cmd_apt_mark()
     local cur prev words cword split comp_args
     _comp_initialize -s -- "$@" || return
 
-    local special i
-    unset -v special # workaround for localvar_inherit
+    local special="" i
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
         if [[ ${words[i]} == @(auto|manual|minimize-manual|showauto|showmanual|hold|unhold|showhold|install|remove|deinstall|purge|showinstall|showremove|showpurge) ]]; then
             special=${words[i]}
             break
         fi
     done
 
-    if [[ -v special ]]; then
+    if [[ $special ]]; then
         case $special in
             auto | manual | unhold)
                 local -A showcmds=([auto]=manual [manual]=auto [unhold]=hold)

completions/aptitude

@@ -18,16 +18,15 @@ _aptitude()
     local cur prev words cword comp_args
     _comp_initialize -- "$@" || return
 
-    local special i
-    unset -v special # workaround for localvar_inherit
+    local special="" i
     for ((i = 1; i < ${#words[@]} - 1; i++)); do
         if [[ ${words[i]} == @(@(|re)install|@(|un)hold|@(|un)markauto|@(dist|full|safe)-upgrade|download|show|forbid-version|purge|remove|changelog|why@(|-not)|keep@(|-all)|build-dep|@(add|remove)-user-tag|versions) ]]; then
             special=${words[i]}
             break
         fi
     done
 
-    if [[ -v special ]]; then
+    if [[ $special ]]; then
         case $special in
             install | hold | markauto | unmarkauto | dist-upgrade | full-upgrade | \
                 safe-upgrade | download | show | changelog | why | why-not | build-dep | \