vim-airline customization: parse substring from current branch name

Question

We're formatting our branch name like feature/HD-1234_tiny_description where "1234" refers to a Jira ticket number. I'd like to only display this number in vim-airline (along with vim-fugitive)

According to the docs:

vim-airline will display the branch-indicator together with the branch name in the statusline, if one of the following plugins is installed:

• fugitive.vim https://github.com/tpope/vim-fugitive
• ...

if a string is provided, it should be the name of a function that takes a string and returns the desired value

let g:airline#extensions#branch#format = 'CustomBranchName'
function! CustomBranchName(name)
    return '[' . a:name . ']'
endfunctionlet

So I'm naively tried

let g:airline#extensions#branch#format = 'JiraTicketNumber'
function! JiraTicketNumber(name)
  return matchstr(name, '/feature\/hd[-_]{1}(\d{4})/i')[1]
endfunction

which returns an error undefined variable : name (roughly translated).

Could anyone give me an helping hand ?

---

Ideally I'd like to return the ticket number only if the branch name starts by "feature" (so fix/... and chore/... would be simply truncated via let g:airline#extensions#branch#format = 1)

Should this work ?

let g:airline#extensions#branch#format = 'JiraTicketNumber'
function! JiraTicketNumber(name)
  if name =~ 'feature'
    return matchstr(name, '/feature\/hd[-_]{1}(\d{4})/i')[1]
  else
    return name
  endif
endfunction

Answer 1

Notice that in the example they use a:name to refer to the argument; in VimScript prior to vim9script you must prefix arguments with a: because you reference them in the "argument namespace" (actually a dictionary).

Try (where I've also touched up the pattern, the =~[#] operator, and used the matchlist function)

let g:airline#extensions#branch#format = 'JiraTicketNumber'
function JiraTicketNumber(name) abort
  if a:name =~# 'feature'
    return matchlist(a:name, 'feature\/HD[-_]\(\d\{4}\)')[1]
  else
    return a:name
  endif
endfunction