How can I invoke another program's bash completion handler for a single subcommand of my program?

Question

Context

I have an arduino-cli wrapper script named ino that reads target/build configuration from:

1. JSON files located in the sketch directory
2. Command-line flags/arguments

It then constructs and exec's the corresponding arduino-cli command-line.

Problem

As a convenience wrapper script, ino isn't intended to support every feature of arduino-cli. So for those tasks that ino doesn't automate, the user can instead invoke arduino-cli indirectly using the cli subcommand of ino.

For example, if the user types the following commands:

% ino cli update
% ino cli core list --all

The ino script will take everything following cli and simply append them to the arduino-cli executable. So they would be equivalent to the following commands:

% arduino-cli update
% arduino-cli core list --all

Since arduino-cli has nice bash completion for all of its subcommands and flags, I would like to hijack the same completion functionality for my ino cli subcommand.

What I've tried

1. The accepted answers here:

   • How do I autocomplete nested, multi-level subcommands?
   • Multi Level Bash Completion
     • These helped me understand how to identify the current subcommand and discriminate the completion results based upon it.
     • However, I couldn't figure out how to then invoke the arduino-cli completion handler using the remaining args.

2. Completion handler derived from accepted answer here:

   • How do I get bash completion for command aliases?
     • See my ino completion handler based on that answer below (Reference 1).
     • This question/answer isn't quite the same, because they can basically just install a completion handler on their alias. I'm needing to "install" one on an argument to a command/alias.
     • This almost seems to work. Try it with xtrace option enabled (set -x), and you can see the arduino-cli command-line is appearing in the args ... but following ino at position $0.
       • E.g., given ino cli core list --all to the wrapper handler, the arduino-cli handler receives ino arduino-cli core list --all. Not sure how to get rid of $0!

Reference

• ino completion wrapper derived from alias-based wrappers

joinstr() {
    local d=${1-} f=${2-}
    shift 2 && printf %s "$f" "${@/#/$d}"
}

complete-subcmd() {
    [[ ${#} -gt 2 ]] || {
        printf "usage:\n\tcomplete-subcmd src-command... -- comp-func dst-command...\n"
        return 1
    }
    # parse the command-line by splitting it into two command-lines
    # of variable length, src-command and dst-command:
    #   1. src-command is the trigger that invokes the real completion
    #      handler, comp-func.
    #   2. dst-command is the leading args of the command-line passed
    #      to the real completion handler, comp-func, to produce the
    #      resulting completion choices.
    unset -v dstparse
    local -a srccmd dstcmd
    local func
    while [[ ${#} -gt 0 ]]; do
        case "${1}" in
        --) 
            # when we reach the delimiter, also shift in comp-func as 
            # the next argument (the real completion handler).
            dstparse=1
            shift
            func=${1:-}
            ;;
        *)
            # if we aren't processing the delimiter, then all other
            # args are appended to either src-command or dst-command.
            if [[ -z ${dstparse} ]]; then
                srccmd+=( "${1}" )
            else
                dstcmd+=( "${1}" )
            fi
            ;;
        esac
        shift
    done
    # if the completer is dynamic and not yet loaded, try to load it
    # automatically using the given command
    if [[ $( type -t "${func}" ) != function ]]; then
        type -p _completion_loader &> /dev/null &&
            _completion_loader "${dstcmd[@]}"
    fi
    local wrap=$( joinstr _ "${srccmd[@]}" | tr -d -c '[A-Za-z_]' )
    # replace our args with dst-command followed by whatever remains
    # from the invoking command-line.
    eval "
        function _${wrap} {
            (( COMP_CWORD+=$(( ${#dstcmd[@]} )) ))
            COMP_WORDS=( "${dstcmd[@]}" \${COMP_WORDS[@]:1} )
            "${func}"
            return 0
        }
    "
    # install this wrapper handler on the first word in src-command
    complete -F "_${wrap}" "${srccmd[0]}"
}

complete-subcmd ino cli -- __start_arduino-cli arduino-cli

• completion.bash from arduino-cli

# bash completion V2 for arduino-cli                          -*- shell-script -*-

__arduino-cli_debug()
{
    if [[ -n ${BASH_COMP_DEBUG_FILE:-} ]]; then
        echo "$*" >> "${BASH_COMP_DEBUG_FILE}"
    fi
}

# Macs have bash3 for which the bash-completion package doesn't include
# _init_completion. This is a minimal version of that function.
__arduino-cli_init_completion()
{
    COMPREPLY=()
    _get_comp_words_by_ref "$@" cur prev words cword
}

# This function calls the arduino-cli program to obtain the completion
# results and the directive.  It fills the 'out' and 'directive' vars.
__arduino-cli_get_completion_results() {
    local requestComp lastParam lastChar args

    # Prepare the command to request completions for the program.
    # Calling ${words[0]} instead of directly arduino-cli allows to handle aliases
    args=("${words[@]:1}")
    requestComp="${words[0]} __completeNoDesc ${args[*]}"

    lastParam=${words[$((${#words[@]}-1))]}
    lastChar=${lastParam:$((${#lastParam}-1)):1}
    __arduino-cli_debug "lastParam ${lastParam}, lastChar ${lastChar}"

    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.
        __arduino-cli_debug "Adding extra empty parameter"
        requestComp="${requestComp} ''"
    fi

    # When completing a flag with an = (e.g., arduino-cli -n=<TAB>)
    # bash focuses on the part after the =, so we need to remove
    # the flag part from $cur
    if [[ "${cur}" == -*=* ]]; then
        cur="${cur#*=}"
    fi

    __arduino-cli_debug "Calling ${requestComp}"
    # Use eval to handle any environment variables and such
    out=$(eval "${requestComp}" 2>/dev/null)

    # Extract the directive integer at the very end of the output following a colon (:)
    directive=${out##*:}
    # Remove the directive
    out=${out%:*}
    if [ "${directive}" = "${out}" ]; then
        # There is not directive specified
        directive=0
    fi
    __arduino-cli_debug "The completion directive is: ${directive}"
    __arduino-cli_debug "The completions are: ${out[*]}"
}

__arduino-cli_process_completion_results() {
    local shellCompDirectiveError=1
    local shellCompDirectiveNoSpace=2
    local shellCompDirectiveNoFileComp=4
    local shellCompDirectiveFilterFileExt=8
    local shellCompDirectiveFilterDirs=16

    if [ $((directive & shellCompDirectiveError)) -ne 0 ]; then
        # Error code.  No completion.
        __arduino-cli_debug "Received error from custom completion go code"
        return
    else
        if [ $((directive & shellCompDirectiveNoSpace)) -ne 0 ]; then
            if [[ $(type -t compopt) = "builtin" ]]; then
                __arduino-cli_debug "Activating no space"
                compopt -o nospace
            else
                __arduino-cli_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
                __arduino-cli_debug "Activating no file completion"
                compopt +o default
            else
                __arduino-cli_debug "No file completion directive not supported in this version of bash"
            fi
        fi
    fi

    if [ $((directive & shellCompDirectiveFilterFileExt)) -ne 0 ]; then
        # File extension filtering
        local fullFilter filter filteringCmd

        # Do not use quotes around the $out variable or else newline
        # characters will be kept.
        for filter in ${out[*]}; do
            fullFilter+="$filter|"
        done

        filteringCmd="_filedir $fullFilter"
        __arduino-cli_debug "File filtering command: $filteringCmd"
        $filteringCmd
    elif [ $((directive & shellCompDirectiveFilterDirs)) -ne 0 ]; then
        # File completion for directories only

        # Use printf to strip any trailing newline
        local subdir
        subdir=$(printf "%s" "${out[0]}")
        if [ -n "$subdir" ]; then
            __arduino-cli_debug "Listing directories in $subdir"
            pushd "$subdir" >/dev/null 2>&1 && _filedir -d && popd >/dev/null 2>&1 || return
        else
            __arduino-cli_debug "Listing directories in ."
            _filedir -d
        fi
    else
        __arduino-cli_handle_standard_completion_case
    fi

    __arduino-cli_handle_special_char "$cur" :
    __arduino-cli_handle_special_char "$cur" =
}

__arduino-cli_handle_standard_completion_case() {
    local tab comp
    tab=$(printf '\t')

    local longest=0
    # Look for the longest completion so that we can format things nicely
    while IFS='' read -r comp; do
        # Strip any description before checking the length
        comp=${comp%%$tab*}
        # Only consider the completions that match
        comp=$(compgen -W "$comp" -- "$cur")
        if ((${#comp}>longest)); then
            longest=${#comp}
        fi
    done < <(printf "%s\n" "${out[@]}")

    local completions=()
    while IFS='' read -r comp; do
        if [ -z "$comp" ]; then
            continue
        fi

        __arduino-cli_debug "Original comp: $comp"
        comp="$(__arduino-cli_format_comp_descriptions "$comp" "$longest")"
        __arduino-cli_debug "Final comp: $comp"
        completions+=("$comp")
    done < <(printf "%s\n" "${out[@]}")

    while IFS='' read -r comp; do
        COMPREPLY+=("$comp")
    done < <(compgen -W "${completions[*]}" -- "$cur")

    # If there is a single completion left, remove the description text
    if [ ${#COMPREPLY[*]} -eq 1 ]; then
        __arduino-cli_debug "COMPREPLY[0]: ${COMPREPLY[0]}"
        comp="${COMPREPLY[0]%% *}"
        __arduino-cli_debug "Removed description from single completion, which is now: ${comp}"
        COMPREPLY=()
        COMPREPLY+=("$comp")
    fi
}

__arduino-cli_handle_special_char()
{
    local comp="$1"
    local char=$2
    if [[ "$comp" == *${char}* && "$COMP_WORDBREAKS" == *${char}* ]]; then
        local word=${comp%"${comp##*${char}}"}
        local idx=${#COMPREPLY[*]}
        while [[ $((--idx)) -ge 0 ]]; do
            COMPREPLY[$idx]=${COMPREPLY[$idx]#"$word"}
        done
    fi
}

__arduino-cli_format_comp_descriptions()
{
    local tab
    tab=$(printf '\t')
    local comp="$1"
    local longest=$2

    # Properly format the description string which follows a tab character if there is one
    if [[ "$comp" == *$tab* ]]; then
        desc=${comp#*$tab}
        comp=${comp%%$tab*}

        # $COLUMNS stores the current shell width.
        # Remove an extra 4 because we add 2 spaces and 2 parentheses.
        maxdesclength=$(( COLUMNS - longest - 4 ))

        # Make sure we can fit a description of at least 8 characters
        # if we are to align the descriptions.
        if [[ $maxdesclength -gt 8 ]]; then
            # Add the proper number of spaces to align the descriptions
            for ((i = ${#comp} ; i < longest ; i++)); do
                comp+=" "
            done
        else
            # Don't pad the descriptions so we can fit more text after the completion
            maxdesclength=$(( COLUMNS - ${#comp} - 4 ))
        fi

        # 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 $maxdesclength ]; then
                desc=${desc:0:$(( maxdesclength - 1 ))}
                desc+="…"
            fi
            comp+="  ($desc)"
        fi
    fi

    # Must use printf to escape all special characters
    printf "%q" "${comp}"
}

__start_arduino-cli()
{
    local cur prev words cword split

    COMPREPLY=()

    # 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
    else
        __arduino-cli_init_completion -n "=:" || return
    fi

    __arduino-cli_debug
    __arduino-cli_debug "========= starting completion logic =========="
    __arduino-cli_debug "cur is ${cur}, words[*] is ${words[*]}, #words[@] is ${#words[@]}, cword is $cword"

    # The user could have moved the cursor backwards on the command-line.
    # We need to trigger completion from the $cword location, so we need
    # to truncate the command-line ($words) up to the $cword location.
    words=("${words[@]:0:$cword+1}")
    __arduino-cli_debug "Truncated words[*]: ${words[*]},"

    local out directive
    __arduino-cli_get_completion_results
    __arduino-cli_process_completion_results
}

if [[ $(type -t compopt) = "builtin" ]]; then
    complete -o default -F __start_arduino-cli arduino-cli
else
    complete -o default -o nospace -F __start_arduino-cli arduino-cli
fi

# ex: ts=4 sw=4 et filetype=sh

Answer 1

UPDATE2:

After I posted this I checked your links and after seeing the accepted answer here, I was thinking I am just old and forget that I just copied this code from that link, and it wasn't me who wrote it. Even the example used there is the same, but investigating the code further, it looks I did write this and used a different approach, and maybe this will help you understand what's going on. As I mentioned at the bottom UPDATE1 section: you need to tune the COMP variables then call the original function

---

Original:

I wrote an 'alias wrapper' script a couple of years ago. The idea is to use the original bash completion with aliases even with parameters. For example:

    alias apti='apt-get install'
    source alias-completion-wrapper _apt_get apti apt-get install
    #here _apt_get is the original completion function

Now you can use tab to complete the package name after apti just like after apt-get install

#alias-completion-wrapper
#Example: . alias-completion-wrapper _apt_get apti apt-get install

comp_function_name="$1"
ali="$2"
shift 2
x="$@"
function_name=`echo _$@ |tr ' ' _`
function="
    function $function_name {
       _completion_loader $1
       (( COMP_CWORD += $# - 1 ))
       COMP_WORDS=( $@ \"\${COMP_WORDS[@]:1}\")
       COMP_LINE=\"\${COMP_WORDS[@]}\"
       let COMP_POINT=\${COMP_POINT}-${#ali}+${#x}
       $comp_function_name
       return 0
    }"
eval "$function"
complete -F $function_name $ali
unset function function_name ali x

To be honest, I can't remember how it works and I didn't commented the script :) But I think you will be able to tune this for your needs.

---

UPDATE1:

As I investigated the code a bit, it looks like the idea is to tune the COMP variables, then call the original function :)

---

UPDATE3:

I had some time, so the modification you need are:

This ${COMP_WORDS[@]} contains the current command line. ${COMP_WORDS[@]:1} cuts off the first word, which is originally the alias/command. As you want to use it after a parameter you have to cut off the parameter too.

COMP_WORDS=( $@ \"\${COMP_WORDS[@]:2}\")

I don't see COMP_LINE and COMP_POINT in the other solution, but as I can recall without those, it doesn't worked well in certain circumstances. So I suppose you need:

COMP_LINE=\"\${COMP_WORDS[@]:1}\"

And here ${#ali} is the length of the command. You need to replace this with the length of your command with the parameter. eg,:"xcmd prm" -> 8 (count the space too)

let COMP_POINT=\${COMP_POINT}-${#ali}+${#x}

Not sure about (( COMP_CWORD += $# - 1 )) either remove the -1 or use -2 or leave it as it is :)

After the modifications, just change the eval to echo and remove the complete -F line. And source the script as described. This way it will echo the function what you can insert into your completion script.