vimscript for Ultisnips+Deoplete compatibility - vim

Question

I'm wondering how to write a function that overloads <TAB>.
First it would do a check to see if there is a snippet that needs to be completed, and if there is a snippet, then expand it.
Otherwise, I would like the function to do a check to see if there is a space before the cursor (or we are on new line) before Tab is pressed. If so, then it should do regular <tab>.
Otherwise, I'd like for it to call
deoplete#manual_complete()
Unless there is already a menu open, in which case, I should be able to tab through it.
Here was my attempt (Which fails completely) and some settings for reference:
let g:ulti_expand_or_jump_res = 0 "default value, just set once
function! Ulti_ExpandOrJump_and_getRes()
call UltiSnips#ExpandSnippetOrJump()
return g:ulti_expand_or_jump_res
endfunction
inoremap <silent><expr> <tab>
\ (Ulti_ExpandOrJump_and_getRes() > 0) ? "\<C-y>"
\ : pumvisible() ? "\<C-n>" :
\ <SID>check_back_space() ? "\<TAB>" :
\ deoplete#manual_complete()
function! s:check_back_space() abort "{{{
let col = col('.') - 1
return !col || getline('.')[col - 1] =~ '\s'
endfunction "}}}
Oddly enough, when I press tab, the bottom right of vim reads that I have typed "^I", which is very strange behavior.
The reason I do not have the ultisnips expand trigger as "tab" is that it disables the use of tab for deoplete (for whatever reason.)

Answer 1

I believe the main issue you're running into is that UltiSnips#ExpandSnippetOrJump() will try to move the cursor and that's a problem from an <expr> mapping in insert mode. Using <C-R>=...<CR> instead should make it work. (At least that's what the example in UltiSnips documentation uses.)
I'd also recommend using a single function to handle all Tab cases instead of a rather long one-liner. That way you can use ifs and document each case specifically.
I also think for the case you expand or jump on UltiSnips, you want to expand to nothing rather than a <C-y>, right?
Putting it all together:
function! HandleTab() abort
" First, try to expand or jump on UltiSnips.
call UltiSnips#ExpandSnippetOrJump()
if g:ulti_expand_or_jump_res > 0
return ""
endif
" Then, check if we're in a completion menu
if pumvisible()
return "\<C-n>"
endif
" Then check if we're indenting.
let col = col('.') - 1
if !col || getline('.')[col - 1] =~ '\s'
return "\<Tab>"
endif
" Finally, trigger deoplete completion.
return deoplete#manual_complete()
endfunction
inoremap <silent> <Tab> <C-R>=HandleTab()<CR>
You might want to review the order of the checks. It seems to me that checking for pumvisible() should be first. Also, checking whether you're indenting is probably cheaper than checking for an UltiSnips expansion, though I guess you could be jumping through fields when you have a space... Anyways, it should be easy to tweak this to make it work.