ftplugin/gitcommit.vim: Experiment providing a custom mapping

Experiment with providing a custom mapping for our Git SHA completion
function. We use <C-x><C-s>.

The custom mapping should set our function as the custom `completefunc`,
call the user completion function by programmatically running
`<C-x><C-u>`, and then unset and restore the previous `completefunc`
value.

This allows us to not clobber a user-defined completion function and
also give ourselves a special custom <C-x> mapping.

Just experimenting for now. Figured out how to get this to work using a
test `ASDF` function along with these resources:
* http://stackoverflow.com/questions/15643234/remapping-tab-completions-in-vim
* https://github.com/ervandew/supertab/blob/master/plugin/supertab.vim
* http://stackoverflow.com/questions/6926034/creating-a-mapping-for-insert-mode-but-not-for-autocomplete-submode

It works. The only problem is that we can't restore the old
`completefunc` value. Thinking about ways to do this, and for now my
most promising idea is to use the `CursorMovedI` autocommand.

1 files changed, 18 insertions, 1 deletions

diff --git a/ftplugin/gitcommit.vim b/ftplugin/gitcommit.vim
index daed923..19577d2 100644
--- a/ftplugin/gitcommit.vim
+++ b/ftplugin/gitcommit.vim
@@ -21,4 +21,21 @@ function! GitSHAComplete(findstart, base)
 	return matches
 endfunction
 
-set completefunc=GitSHAComplete
+function! StartGitSHACompletion()
+	let old_completefunc = &completefunc
+
+	set completefunc=GitSHAComplete
+	return "\<C-x>\<C-u>"
+
+	let &completefunc = old_completefunc
+endfunction
+
+function! ASDF()
+	return "\<C-p>"
+endfunction
+
+" inoremap <expr> <C-x><C-s> StartGitSHACompletion()
+" inoremap <C-x><C-s> <C-r>=StartGitSHACompletion()<CR>
+inoremap <expr> <C-x><C-s> StartGitSHACompletion()
+
+inoremap <C-v> <C-r>=ASDF()<CR>