Add extension for fern.vim

autoload/airline/extensions.vim

@@ -165,6 +165,11 @@ function! airline#extensions#load()
     call add(s:loaded_ext, 'gina')
   endif
 
+  if get(g:, 'fern_loaded', 0) && get(g:, 'airline#extensions#fern#enabled', 1)
+    call airline#extensions#fern#init(s:ext)
+    call add(s:loaded_ext, 'fern')
+  endif
+
   if exists(':NetrwSettings')
     call airline#extensions#netrw#init(s:ext)
     call add(s:loaded_ext, 'netrw')

autoload/airline/extensions/fern.vim

@@ -0,0 +1,36 @@
+" MIT License. Copyright (c) 2013-2020
+" Plugin: https://github.com/lambdalisue/fern.vim
+" vim: et ts=2 sts=2 sw=2
+
+scriptencoding utf-8
+if !get(g:, 'fern_loaded', 0)
+  finish
+endif
+
+function! airline#extensions#fern#apply(...) abort
+  if (&ft =~# 'fern')
+    let spc = g:airline_symbols.space
+    let fri = fern#fri#parse(expand('%f'))
+
+    call a:1.add_section('airline_a', spc.'fern'.spc)
+    if exists('*airline#extensions#branch#get_head')
+      call a:1.add_section('airline_b', spc.'%{airline#extensions#branch#get_head()}'.spc)
+    else
+      call a:1.add_section('airline_b', '')
+    endif
+    if !(fri.authority =~# '^drawer')
+      let abspath = substitute(fri.path, 'file://', '', '')
+      call a:1.add_section('airline_c', spc.fnamemodify(abspath, ':~'))
+      call a:1.split()
+      if len(get(g:, 'fern#comparators', {}))
+        call a:1.add_section('airline_y', spc.'%{fern#comparator}'.spc)
+      endif
+    endif
+    return 1
+  endif
+endfunction
+
+function! airline#extensions#fern#init(ext) abort
+  let g:fern_force_overwrite_statusline = 0
+  call a:ext.add_statusline_func('airline#extensions#fern#apply')
+endfunction