style(bash-v2): various cleanups (spf13#1702)

* use arithmetic evaluation in numeric context

* remove unnecessary $ from array index variables

* [[ ]] over [ ], == over =, remove unnecessary quoting

* use ${foo-} rather than ${foo:-} in emptiness check

The result of the expansion is null no matter if the variable is unset
or null in both cases; the former form is arguably easier on the eye.

* remove unnecessary trailing linefeed removal

No longer needed as of f464d6c, saves
a subshell.

* use herestring in activehelp extraction

Herestrings read cleaner than process substitutions, and work in posix
mode (but we do and will have some process substitutions so this doesn't
matter much). Both approaches may end up using temporary files.

bash_completionsV2.go

@@ -38,7 +38,7 @@ func genBashComp(buf io.StringWriter, name string, includeDesc bool) {
 
 __%[1]s_debug()
 {
-    if [[ -n ${BASH_COMP_DEBUG_FILE:-} ]]; then
+    if [[ -n ${BASH_COMP_DEBUG_FILE-} ]]; then
         echo "$*" >> "${BASH_COMP_DEBUG_FILE}"
     fi
 }
@@ -65,7 +65,7 @@ __%[1]s_get_completion_results() {
     lastChar=${lastParam:$((${#lastParam}-1)):1}
     __%[1]s_debug "lastParam ${lastParam}, lastChar ${lastChar}"
 
-    if [ -z "${cur}" ] && [ "${lastChar}" != "=" ]; then
+    if [[ -z ${cur} && ${lastChar} != = ]]; then
         # If the last parameter is complete (there is a space following it)
         # We add an extra empty parameter so we can indicate this to the go method.
         __%[1]s_debug "Adding extra empty parameter"
@@ -75,7 +75,7 @@ __%[1]s_get_completion_results() {
     # When completing a flag with an = (e.g., %[1]s -n=<TAB>)
     # bash focuses on the part after the =, so we need to remove
     # the flag part from $cur
-    if [[ "${cur}" == -*=* ]]; then
+    if [[ ${cur} == -*=* ]]; then
         cur="${cur#*=}"
     fi
 
@@ -87,7 +87,7 @@ __%[1]s_get_completion_results() {
     directive=${out##*:}
     # Remove the directive
     out=${out%%:*}
-    if [ "${directive}" = "${out}" ]; then
+    if [[ ${directive} == "${out}" ]]; then
         # There is not directive specified
         directive=0
     fi
@@ -102,21 +102,21 @@ __%[1]s_process_completion_results() {
     local shellCompDirectiveFilterFileExt=%[6]d
     local shellCompDirectiveFilterDirs=%[7]d
 
-    if [ $((directive & shellCompDirectiveError)) -ne 0 ]; then
+    if (((directive & shellCompDirectiveError) != 0)); then
         # Error code.  No completion.
         __%[1]s_debug "Received error from custom completion go code"
         return
     else
-        if [ $((directive & shellCompDirectiveNoSpace)) -ne 0 ]; then
-            if [[ $(type -t compopt) = "builtin" ]]; then
+        if (((directive & shellCompDirectiveNoSpace) != 0)); then
+            if [[ $(type -t compopt) == builtin ]]; then
                 __%[1]s_debug "Activating no space"
                 compopt -o nospace
             else
                 __%[1]s_debug "No space directive not supported in this version of bash"
             fi
         fi
-        if [ $((directive & shellCompDirectiveNoFileComp)) -ne 0 ]; then
-            if [[ $(type -t compopt) = "builtin" ]]; then
+        if (((directive & shellCompDirectiveNoFileComp) != 0)); then
+            if [[ $(type -t compopt) == builtin ]]; then
                 __%[1]s_debug "Activating no file completion"
                 compopt +o default
             else
@@ -130,7 +130,7 @@ __%[1]s_process_completion_results() {
     local activeHelp=()
     __%[1]s_extract_activeHelp
 
-    if [ $((directive & shellCompDirectiveFilterFileExt)) -ne 0 ]; then
+    if (((directive & shellCompDirectiveFilterFileExt) != 0)); then
         # File extension filtering
         local fullFilter filter filteringCmd
 
@@ -143,13 +143,12 @@ __%[1]s_process_completion_results() {
         filteringCmd="_filedir $fullFilter"
         __%[1]s_debug "File filtering command: $filteringCmd"
         $filteringCmd
-    elif [ $((directive & shellCompDirectiveFilterDirs)) -ne 0 ]; then
+    elif (((directive & shellCompDirectiveFilterDirs) != 0)); then
         # File completion for directories only
 
-        # Use printf to strip any trailing newline
         local subdir
-        subdir=$(printf "%%s" "${completions[0]}")
-        if [ -n "$subdir" ]; then
+        subdir=${completions[0]}
+        if [[ -n $subdir ]]; then
             __%[1]s_debug "Listing directories in $subdir"
             pushd "$subdir" >/dev/null 2>&1 && _filedir -d && popd >/dev/null 2>&1 || return
         else
@@ -164,7 +163,7 @@ __%[1]s_process_completion_results() {
     __%[1]s_handle_special_char "$cur" =
 
     # Print the activeHelp statements before we finish
-    if [ ${#activeHelp[*]} -ne 0 ]; then
+    if ((${#activeHelp[*]} != 0)); then
         printf "\n";
         printf "%%s\n" "${activeHelp[@]}"
         printf "\n"
@@ -188,17 +187,17 @@ __%[1]s_extract_activeHelp() {
     local endIndex=${#activeHelpMarker}
 
     while IFS='' read -r comp; do
-        if [ "${comp:0:endIndex}" = "$activeHelpMarker" ]; then
+        if [[ ${comp:0:endIndex} == $activeHelpMarker ]]; then
             comp=${comp:endIndex}
             __%[1]s_debug "ActiveHelp found: $comp"
-            if [ -n "$comp" ]; then
+            if [[ -n $comp ]]; then
                 activeHelp+=("$comp")
             fi
         else
             # Not an activeHelp line but a normal completion
             completions+=("$comp")
         fi
-    done < <(printf "%%s\n" "${out}")
+    done <<<"${out}"
 }
 
 __%[1]s_handle_completion_types() {
@@ -254,7 +253,7 @@ __%[1]s_handle_standard_completion_case() {
     done < <(printf "%%s\n" "${completions[@]}")
 
     # If there is a single completion left, remove the description text
-    if [ ${#COMPREPLY[*]} -eq 1 ]; then
+    if ((${#COMPREPLY[*]} == 1)); then
         __%[1]s_debug "COMPREPLY[0]: ${COMPREPLY[0]}"
         comp="${COMPREPLY[0]%%%%$tab*}"
         __%[1]s_debug "Removed description from single completion, which is now: ${comp}"
@@ -271,8 +270,8 @@ __%[1]s_handle_special_char()
     if [[ "$comp" == *${char}* && "$COMP_WORDBREAKS" == *${char}* ]]; then
         local word=${comp%%"${comp##*${char}}"}
         local idx=${#COMPREPLY[*]}
-        while [[ $((--idx)) -ge 0 ]]; do
-            COMPREPLY[$idx]=${COMPREPLY[$idx]#"$word"}
+        while ((--idx >= 0)); do
+            COMPREPLY[idx]=${COMPREPLY[idx]#"$word"}
         done
     fi
 }
@@ -298,7 +297,7 @@ __%[1]s_format_comp_descriptions()
 
             # Make sure we can fit a description of at least 8 characters
             # if we are to align the descriptions.
-            if [[ $maxdesclength -gt 8 ]]; then
+            if ((maxdesclength > 8)); then
                 # Add the proper number of spaces to align the descriptions
                 for ((i = ${#comp} ; i < longest ; i++)); do
                     comp+=" "
@@ -310,8 +309,8 @@ __%[1]s_format_comp_descriptions()
 
             # If there is enough space for any description text,
             # truncate the descriptions that are too long for the shell width
-            if [ $maxdesclength -gt 0 ]; then
-                if [ ${#desc} -gt $maxdesclength ]; then
+            if ((maxdesclength > 0)); then
+                if ((${#desc} > maxdesclength)); then
                     desc=${desc:0:$(( maxdesclength - 1 ))}
                     desc+="…"
                 fi
@@ -332,9 +331,9 @@ __start_%[1]s()
     # Call _init_completion from the bash-completion package
     # to prepare the arguments properly
     if declare -F _init_completion >/dev/null 2>&1; then
-        _init_completion -n "=:" || return
+        _init_completion -n =: || return
     else
-        __%[1]s_init_completion -n "=:" || return
+        __%[1]s_init_completion -n =: || return
     fi
 
     __%[1]s_debug