How to print a message after `autocmd` is done

Question

I'm using ctags to generate tag file so that I can jump to declaration or to definition while working with C/C++ project.

To make ctags work automatically while entering vim, I add such a line in my .vimrc:

autocmd VimEnter * silent! !eval 'ctags -R --c++-kinds=+p --fields=+iaS --extra=+q --language-force=C++ -o newtags; mv newtags .tags;' &

As you see, this command won't block because of &.

Now, I want to make sure that a message will be printed at the bottom of the window of vim after this command is done. How could I do this?

Answer 1

Try it as a background job (:help job). Maybe like this:

function CtagsExit(cwd, job_id, exit_code)
    if a:exit_code == 0
        call rename(a:cwd . '/newtags', a:cwd . '/.tags')
        echo "Ctags finished with 0"
    else
        echo "Ctags finished with " . a:exit_code . " (execute :messages to see output)"
    endif
endfunction

function CtagsOutput(channel, data)
    echomsg a:data
endfunction

function CtagsStartup()
    let cmdline='ctags -R --c++-kinds=+p --fields=+iaS --extra=+q --language-force=C++ -o newtags'
    let options = {
                \   'in_io': "null",
                \   'out_cb': "CtagsOutput",
                \   'err_cb': "CtagsOutput",
                \   'exit_cb': function('CtagsExit', [ getcwd() ])
                \ }
    call job_start(cmdline, options)
endfunction

autocmd VimEnter * call CtagsStartup()

Update: Handle changing directory while ctags is running. Update 2: Handle output.