From 6c704f4b780e2b687dd21b24a19f598dde06dc22 Mon Sep 17 00:00:00 2001
From: Neil Lambert <contact@neillambert.com>
Date: Wed, 30 Oct 2024 13:21:02 -0400
Subject: [PATCH] fix vim-airline/fern does not update the branch name as you
 navigate through fern, and theme fern inactive windows too (#2698)

Co-authored-by: Neil Lambert <nlambert@pm.me>
---
 autoload/airline/extensions/fern.vim | 57 ++++++++++++++++++----------
 1 file changed, 37 insertions(+), 20 deletions(-)

diff --git a/autoload/airline/extensions/fern.vim b/autoload/airline/extensions/fern.vim
index 8b5562af..a1878e32 100644
--- a/autoload/airline/extensions/fern.vim
+++ b/autoload/airline/extensions/fern.vim
@@ -7,30 +7,47 @@ if !get(g:, 'loaded_fern', 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
+function! airline#extensions#fern#apply_active(...) abort
+  " check if current buffer is both fern and active
+  if (&ft =~# 'fern') && a:2.active ==# '1'
+    call airline#extensions#fern#configure_sections(a:1, a:2)
     return 1
   endif
 endfunction
 
+
+function! airline#extensions#fern#apply_inactive(...) abort
+  " check if referenced buffer is both fern and inactive
+  if getbufvar(a:2.bufnr, '&filetype') ==# 'fern' && a:2.active ==# '0'
+    call airline#extensions#fern#configure_sections(a:1, a:2)
+    return 1
+  endif
+endfunction
+
+function! airline#extensions#fern#configure_sections(win, context) abort
+  let spc = g:airline_symbols.space
+  let fri = fern#fri#parse(bufname(a:context.bufnr))
+  let abspath = substitute(fri.path, 'file://', '', '')
+  call a:win.add_section('airline_a', spc.'fern'.spc)
+  if exists('*airline#extensions#branch#get_head')
+    " because fern navigation changes an internal _fri_ and not the working directory
+    " we need to give it some help so the branch name gets updated
+    execute 'lcd' abspath 
+    call a:win.add_section('airline_b', spc.'%{airline#extensions#branch#get_head()}'.spc)
+  else
+    call a:win.add_section('airline_b', '')
+  endif
+  if !(fri.authority =~# '^drawer')
+    call a:win.add_section('airline_c', spc.fnamemodify(abspath, ':~'))
+    call a:win.split()
+    if len(get(g:, 'fern#comparators', {}))
+      call a:win.add_section('airline_y', spc.'%{fern#comparator}'.spc)
+    endif
+  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')
+  call a:ext.add_statusline_func('airline#extensions#fern#apply_active')
+  call a:ext.add_inactive_statusline_func('airline#extensions#fern#apply_inactive')
 endfunction