ks/precompute-completion

Hi,

As a distro user, I don’t think I would be able to use it until there is a command to update the installed completion, to call after adding a new git command to my $PATH. This could mean:

 - git-completion.bash.generate learns to read the .in file and
   write the completion script to arbitrary paths (or just always
   uses stdin and stdout?)

 - distros install git-completion.bash.{generate,in} to /usr/share/git-core

 - distros install a simple completion script to /etc/bash_completion.d
   that passes the buck, e.g.

-- %< -- # bash completion support for core Git. # # Run update-git-completion to generate these files. # __git_user_completion=~/.cache/git-core/git-completion.bash __git_system_completion=/var/cache/git-core/git-completion.bash

if test -r "$__git_user_completion"
then
	. "$__git_user_completion"
elif test -r "$__git_system_completion"
then
	. "$__git_system_completion"
fi
-- >% --

 - new update-git-completion script, something like this:

-- %< --
#!/bin/sh
USAGE="update-git-completion {--system | --user | <filename>}"
datadir=/usr/share/git-core
die() {
	echo >&2 "$*"
	exit 1
}

if ! test $# -eq 1
then
	die "usage: $USAGE"
fi

if test "$1" = "--system"
then
	output=/var/cache/git-core/git-completion.bash
elif test "$1" = "--user"
then
	output=$HOME/.cache/git-core/git-completion.bash
else
	output=$1
fi

rm -f "$output+" || die "cannot remove $output+"
sh "$datadir"/git-completion.bash.generate \
	< "$datadir"/git-completion.bash.in \
	> "$output+" || die "failed to generate completion script"
bash -n "$output+" || {
	rm -f "$output+"
	die "generated script fails syntax check"
}
mv -f "$output+" "$output" || {
	rm -f "$output+"
	die "failed to install completion script"
}
-- >% --

Thoughts?