how to re-use existing completion with recent bash-completion?

how to re-use existing completion (for example for git) with recent versions of package bash-completion

Add the following lines to your ~/.bashrc:

_completion_loader git
eval $(complete -p git | perl -pe 's/(\s)git$/$1git.home/')

Explanation:

bash-completion uses a dynamic loading of completions since 1.90. So, the git compspec unavailable before your typing git,Space,Tab.

Try:

bash
complete -p git # bash: complete: git: no completion specification
git<space><tab>
complete -p git # complete -o bashdefault -o default -o nospace -F __git_wrap__git_main git

_completion_loader git imitates git,Space,Tab (i.e. loads a compspec for git)

complete -p git | perl -pe 's/(\s)git$/$1git.home/' builds a compspec for git.home (replaces git to git.home in a git's compspec)

eval execute the resulting compspec.

Type git.home,Space,pTab. You should see:

popt   pull   push

But git.home log,Space,Tab produces:

fatal: Not a git repository (or any of the parent directories): .git HEAD

This message is a result of the git completion bug. There is a fix in the upstream: completion: silence "fatal: Not a git repository" error

Looks like another question:)

_githome(){ 
   GIT_DIR=$HOME/.git.home
   complete -o default -o nospace -F _git git.home
 }

doesn't work as expected. You set GIT_DIR for current session. Try with your solution:

bash
git clone git://git.debian.org/git/bash-completion/bash-completion.git ~/bash-completion
cd ~/bash-completion
git log<space><tab> # completion for current repo
git.home log<space><tab> # completion for GIT_DIR
git log<space><tab> # completion for GIT_DIR

updated

solution for alias git.home, which operates with ~/.git.home as repo.

partially based on this answer.

add to ~/.bashrc:

alias git.home='git --git-dir=$HOME/.git.home/'

_completion_loader git
eval "$(complete -p git | sed -r 's/(\s)git$/\1git.home/')"

eval "$(type __gitdir | 
  sed '1d;1,/if/s|if|if [[ "$COMP_LINE" == "git.home "* ]]; then\necho "$HOME/.git.home"\nelif|')"

---

explanation of last eval (for other lines see answer):

we are patching the function __gitdir(), which returns a path to the git repo dir. from:

$ type __gitdir | head -n 4
__gitdir is a function
__gitdir () 
{ 
    if [ -z "${1-}" ]; then

to:

$ type __gitdir | head -n 7
__gitdir is a function
__gitdir () 
{ 
    if [[ "$COMP_LINE" == "git.home "* ]]; then
        echo "$HOME/.git.home";
    else
        if [ -z "${1-}" ]; then

i.e., if command starts with a "git.home ", function returns $HOME/.git.home.