execute() error neovim with substitute command

user_13394797 0
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I can't seem to figure out how to set a variable equal to the number of matches in a file.

I have tried this

let a=execute('%s/<++>//ne')

but it won't work (throws this error:

Error detected while processing function myfunctions#Tab:
line    2:
E523: Not allowed here

). I want a variable with the number of matches for a regular expression and I can't seem to find a way to use the execute() function with the substitute command. (execute('%s/test//ne') throws an error too).

EDIT: I am trying to run this inside a function that is called as an <expr> mapping. The full function body is this (control characters properly inserted):

function! myfunctions#Tab()
    let a=execute('%s/<++>//ne')
    if a > 0
        return "/<++>^M:noh^Mc4l"
    else
        return "^I"
    endif
endfunction

The goal is to insert a tab if the pattern <++> doesn't exist, and if it does, then find it and replace it. I mapped it like this:

inoremap <expr> <tab> myfunctions#Tab()
neovim vim
1 Answers

The reason why you're hitting this error is that a function called in an <expr> mapping is restricted and can't modify the current buffer.

From :help :map-expression:

Be very careful about side effects! The expression is evaluated while obtaining characters, you may very well make the command dysfunctional.

For this reason the following is blocked:

  • Changing the buffer text textlock.
  • Editing another buffer.
  • The :normal command.
  • Moving the cursor is allowed, but it is restored afterwards.

What is triggering this situation is your :s command. Even though you're using the /n flag, which does not modify the buffer, the :s command generally introduces modification and as such is completely blocked under textlock.

If what you're trying to do is jump to the next <++> on tab, then the best option is to use the search() function, which will move your cursor to the next match and return the line number (non-zero) if a match was found.

Since an <expr> mapping doesn't preserve cursor movement, you should use a normal mapping instead.

This gets tricky quickly though... It turns out this is one of the hardest mappings to get right...

But the gist of it is: you'll want to escape Insert mode temporarily with CTRL-\ CTRL-O and call your function. There, you can do your search(). If the search matches, you'll need to call :stopinsert to interrupt the temporary escape from Insert mode (essentially making it permanent). Then you can run the c4l command, but you need to do so using feedkeys(), since it will leave you in Normal mode at the end.

If there's no match and you want a tab character inserted, you can then use feedkeys() to insert the tab character.

Putting it all together:

function! myfunctions#Tab()
  if search('<++>')
    stopinsert
    call feedkeys('c4l', 'n')
  else
    call feedkeys("\t", 'n')
  endif
endfunction

inoremap <silent> <Tab> <C-\><C-o>:call myfunctions#Tab()<CR>
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