always use [[ ... ]] and not [ ... ] in bash completions

shell/completion.bash

@@ -35,9 +35,9 @@ fi
 bind '"\e[0n": redraw-current-line'
 
 __fzf_comprun() {
-  if [ "$(type -t _fzf_comprun 2>&1)" = function ]; then
+  if [[ "$(type -t _fzf_comprun 2>&1)" = function ]]; then
     _fzf_comprun "$@"
-  elif [ -n "$TMUX_PANE" ] && { [ "${FZF_TMUX:-0}" != 0 ] || [ -n "$FZF_TMUX_OPTS" ]; }; then
+  elif [[ -n "$TMUX_PANE" ]] && { [[ "${FZF_TMUX:-0}" != 0 ]] || [[ -n "$FZF_TMUX_OPTS" ]]; }; then
     shift
     fzf-tmux ${FZF_TMUX_OPTS:--d${FZF_TMUX_HEIGHT:-40%}} -- "$@"
   else
@@ -140,14 +140,14 @@ _fzf_handle_dynamic_completion() {
   orig_cmd="$1"
   orig_var="_fzf_orig_completion_$cmd"
   orig="${!orig_var##*#}"
-  if [ -n "$orig" ] && type "$orig" > /dev/null 2>&1; then
+  if [[ -n "$orig" ]] && type "$orig" > /dev/null 2>&1; then
     $orig "$@"
-  elif [ -n "$_fzf_completion_loader" ]; then
+  elif [[ -n "$_fzf_completion_loader" ]]; then
     orig_complete=$(complete -p "$orig_cmd" 2> /dev/null)
     _completion_loader "$@"
     ret=$?
     # _completion_loader may not have updated completion for the command
-    if [ "$(complete -p "$orig_cmd" 2> /dev/null)" != "$orig_complete" ]; then
+    if [[ "$(complete -p "$orig_cmd" 2> /dev/null)" != "$orig_complete" ]]; then
       __fzf_orig_completion < <(complete -p "$orig_cmd" 2> /dev/null)
       if [[ "$__fzf_nospace_commands" = *" $orig_cmd "* ]]; then
         eval "${orig_complete/ -F / -o nospace -F }"
@@ -171,17 +171,17 @@ __fzf_generic_path_completion() {
 
     [[ $base = *"/"* ]] && dir="$base"
     while true; do
-      if [ -z "$dir" ] || [ -d "$dir" ]; then
+      if [[ -z "$dir" ]] || [[ -d "$dir" ]]; then
         leftover=${base/#"$dir"}
         leftover=${leftover/#\/}
-        [ -z "$dir" ] && dir='.'
-        [ "$dir" != "/" ] && dir="${dir/%\//}"
+        [[ -z "$dir" ]] && dir='.'
+        [[ "$dir" != "/" ]] && dir="${dir/%\//}"
         matches=$(eval "$1 $(printf %q "$dir")" | FZF_DEFAULT_OPTS="--height ${FZF_TMUX_HEIGHT:-40%} --reverse --bind=ctrl-z:ignore $FZF_DEFAULT_OPTS $FZF_COMPLETION_OPTS $2" __fzf_comprun "$4" -q "$leftover" | while read -r item; do
           printf "%q$3 " "$item"
         done)
         matches=${matches% }
         [[ -z "$3" ]] && [[ "$__fzf_nospace_commands" = *" ${COMP_WORDS[0]} "* ]] && matches="$matches "
-        if [ -n "$matches" ]; then
+        if [[ -n "$matches" ]]; then
           COMPREPLY=( "$matches" )
         else
           COMPREPLY=( "$cur" )
@@ -234,7 +234,7 @@ _fzf_complete() {
 
     selected=$(FZF_DEFAULT_OPTS="--height ${FZF_TMUX_HEIGHT:-40%} --reverse --bind=ctrl-z:ignore $FZF_DEFAULT_OPTS $FZF_COMPLETION_OPTS $str_arg" __fzf_comprun "${rest[0]}" "${args[@]}" -q "$cur" | $post | tr '\n' ' ')
     selected=${selected% } # Strip trailing space not to repeat "-o nospace"
-    if [ -n "$selected" ]; then
+    if [[ -n "$selected" ]]; then
       COMPREPLY=("$selected")
     else
       COMPREPLY=("$cur")
@@ -330,7 +330,7 @@ __fzf_defc() {
   opts="$3"
   orig_var="_fzf_orig_completion_${cmd//[^A-Za-z0-9_]/_}"
   orig="${!orig_var}"
-  if [ -n "$orig" ]; then
+  if [[ -n "$orig" ]]; then
     printf -v def "$orig" "$func"
     eval "$def"
   else