branch: configure what additional checks to run

Allow to customize, whether to check the untracked status of a file or
whether the current repository is clean.

fixes #1910

autoload/airline/extensions/branch.vim

@@ -180,6 +180,7 @@ function! s:update_untracked()
   endif
 
   let needs_update = 1
+  let vcs_checks   = get(g:, "airline#extensions#branch#vcs_checks", ["untracked", "dirty"])
   for vcs in keys(s:vcs_config)
     if file =~ s:vcs_config[vcs].exclude
       " Skip check for files that live in the exclude directory
@@ -202,9 +203,13 @@ function! s:update_untracked()
     " invalidated again before s:update_untracked is called, then we lose the
     " result of the previous call, i.e. the head string is not updated. It
     " doesn't happen often in practice, so we let it be.
+    if index(vcs_checks, 'untracked') > -1
       call airline#async#vcs_untracked(config, file, vcs)
+    endif
     " Check clean state of repo
+    if index(vcs_checks, 'dirty') > -1
       call airline#async#vcs_clean(config.dirty, file, vcs)
+    endif
   endfor
 endfunction
 

doc/airline.txt

@@ -514,6 +514,16 @@ characters.
     endif
     return b:perforce_client
   endfunction
+>
+* configure additional vcs checks to run
+  By default, vim-airline will check if the current edited file is untracked
+  in the repository. If so, it will append the `g:airline_symbols.notexists`
+  symbol to the branch name.
+  In addition, it will check if the repository is clean, else it will append
+  the `g:airline_symbols.dirty` symbol to the branch name (if the current file
+  is not untracked). Configure, by setting the following variable: >
+
+  let g:airline#extensions#branch#vcs_checks = ['untracked', 'dirty']
 <
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 vim-bufferline <https://github.com/bling/vim-bufferline>