How to add a fallback when :b buffer change fails

Question

I have 2 ways to open a file for editing:

1. :b <filename> to switch to an opened buffer -- imagine that I have a lot of folders containing index.html so by using :b I know I am working on the one that I should be working on.

2. Fuzzy File Search (:FZF) just in case I haven't opened the file or I have killed the buffer with :bd.

My question: Is there a way to automate, such that if :b <filename> fails (E94: No matching buffer), nvim will call :FZF and use <filename> to search?

P.S. It'd be best if I used :b107 and I mistyped the number, FZF will not be triggered. (distinguishing cases whether I use :b with string or number)

Answer 1

You can't change the way the :b command works, but you can create an alternative :B command, and then create an abbreviation to always use the :B command when you type :b.

The below works by first trying using the :b command, and if the E94 error is thrown, doing a :FZF instead:

function! BWithFallback(buffer_name) abort
  " Check if the input is a number or a string
  if a:buffer_name =~# '^\d\+$'
    execute 'b' a:buffer_name
  else
    try
      " Try opening the buffer
      execute 'b' a:buffer_name
    catch /E94/
      " If the buffer didn't exist, try doing a fuzzy file search
      " using the command provided by the OP.
      execute 'FZF -q' a:buffer_name
    endtry
  endif
endfunction

" Create new :B command. You could also use -complete=file if you prefer
command! -nargs=1 -complete=buffer B call BWithFallback('<args>')

" When you type :b, replace it with :B
cnoreabbrev <expr> b (getcmdtype() == ':' && getcmdline() ==# 'b') ? 'B' : b