custom snippet extender Ultisnips

Question

Suppose I have a snippet:

snippet prg 
    !This is file : `!v expand('%:t:r')`
    ! Author= `!v expand($USER)`
    ! Started at: `date +%d.%m.%y`
    ! Last Modified : Sun 16 Jun 2019 12:30:58 IST
    !
    Program  ${1:<++`!v expand('%:t:r')`}
    Implicit None
    ${2}
    End Program  ${1/([^\n$]+).*/$1/}
endsnippet
...

and in vimrc, i have: let g:UltiSnipsExpandTrigger="<c-a>"

which is working fine.

Now, besides this, I am trying to have a keymap, like say, "prg in insertmode, which will expand this snippet for me. eg:

inoremap "prg :some_magic_(expand_snippet_prg)

any idea how to do this?

Answer 1

Use remap to trigger expansion

imap "prg prg<c-a>

or

exe printf('imap "prg prg%s',  g:UltiSnipsExpandTrigger)

But not this:

imap <expr> "prg 'prg' . g:UltiSnipsExpandTrigger

g:UltiSnipsExpandTrigger is a variable, map won't figure out special key code of it's value for you.

Manual expansion

inoremap "prg prg<c-r>=UltiSnips#ExpandSnippet()<cr>

You can't use <expr> here, as <expr> can't change buffer text.

You dont need to call expand on enviroment variable, $USER is enough.