Respect drawer width applied manually when restore the width

Close #309

Author: lambdalisue

autoload/fern/internal/drawer/auto_resize.vim

@@ -5,22 +5,35 @@ function! fern#internal#drawer#auto_resize#init() abort
 
   augroup fern_internal_drawer_init
     autocmd! * <buffer>
-    autocmd BufEnter <buffer> call s:resize()
-    autocmd BufLeave <buffer> call s:resize()
+    autocmd BufEnter <buffer> call s:load_width()
+    autocmd BufLeave <buffer> call s:save_width()
   augroup END
 endfunction
 
 if has('nvim')
-  function! s:is_relative() abort
+  function! s:should_ignore() abort
     return nvim_win_get_config(win_getid()).relative !=# ''
   endfunction
-
-  function! s:resize() abort
-    if s:is_relative()
-      return
-    endif
-    call fern#internal#drawer#resize()
-  endfunction
 else
-  let s:resize = funcref('fern#internal#drawer#resize')
+  function! s:should_ignore() abort
+    return 0
+  endfunction
 endif
+
+function! s:save_width() abort
+  if s:should_ignore()
+    return
+  endif
+  let t:fern_drawer_auto_resize_width = winwidth(0)
+endfunction
+
+function! s:load_width() abort
+  if s:should_ignore()
+    return
+  endif
+  if !exists('t:fern_drawer_auto_resize_width')
+    call fern#internal#drawer#resize()
+  else
+    execute 'vertical resize' t:fern_drawer_auto_resize_width
+  endif
+endfunction

doc/fern.txt

@@ -422,8 +422,7 @@ VARIABLE						*fern-variable*
 	Default: 0
 
 *g:fern#disable_drawer_auto_resize*
-	Set 1 to disable automatically resize drawer on |BufEnter| and
-	|BufLeave| autocmd.
+	Set 1 to disable automatically resize drawer on |BufEnter| autocmd.
 
 	Note that this feature is automatically disabled on floating windows
 	of Neovim to avoid unwilling resize reported as #294