allow to show the statusline on top

This is an experimental feature that allows to display the statusline in
the tabline. It might still be a bit rough, but seems to work so far.

Remaining problem:
- Mode changes are not immediately detected, only after moving the
  cursor

fixes #1388
closes #1867

autoload/airline/extensions/branch.vim

@@ -88,7 +88,8 @@ function! s:update_git_branch()
 
   let s:vcs_config['git'].branch = exists("*FugitiveHead") ?
         \ FugitiveHead(s:sha1size) : fugitive#head(s:sha1size)
-  if s:vcs_config['git'].branch is# 'master' && winwidth(0) < 81
+  if s:vcs_config['git'].branch is# 'master' &&
+        \ airline#util#winwidth() < 81
     " Shorten default a bit
     let s:vcs_config['git'].branch='mas'
   endif

autoload/airline/extensions/default.vim

@@ -19,7 +19,7 @@ let s:layout = get(g:, 'airline#extensions#default#layout', [
 
 function! s:get_section(winnr, key, ...)
   if has_key(s:section_truncate_width, a:key)
-    if winwidth(a:winnr) < s:section_truncate_width[a:key]
+    if airline#util#winwidth(a:winnr) < s:section_truncate_width[a:key]
       return ''
     endif
   endif

autoload/airline/extensions/hunks.vim

@@ -66,7 +66,7 @@ function! airline#extensions#hunks#get_hunks()
   " Cache values, so that it isn't called too often
   if exists("b:airline_hunks") &&
     \ get(b:,  'airline_changenr', 0) == b:changedtick &&
-    \ winwidth(0) == get(s:, 'airline_winwidth', 0) &&
+    \ airline#util#winwidth() == get(s:, 'airline_winwidth', 0) &&
     \ get(b:, 'source_func', '') isnot# 's:get_hunks_signify' &&
     \ get(b:, 'source_func', '') isnot# 's:get_hunks_gitgutter' &&
     \ get(b:, 'source_func', '') isnot# 's:get_hunks_empty' &&
@@ -77,14 +77,14 @@ function! airline#extensions#hunks#get_hunks()
   let string = ''
   if !empty(hunks)
     for i in [0, 1, 2]
-      if (s:non_zero_only == 0 && winwidth(0) > 100) || hunks[i] > 0
+      if (s:non_zero_only == 0 && airline#util#winwidth() > 100) || hunks[i] > 0
         let string .= printf('%s%s ', s:hunk_symbols[i], hunks[i])
       endif
     endfor
   endif
   let b:airline_hunks = string
   let b:airline_changenr = b:changedtick
-  let s:airline_winwidth = winwidth(0)
+  let s:airline_winwidth = airline#util#winwidth()
   return string
 endfunction
 

autoload/airline/extensions/nrrwrgn.vim

@@ -19,7 +19,7 @@ function! airline#extensions#nrrwrgn#apply(...)
       let dict=nrrwrgn#NrrwRgnStatus()
       let vmode = { 'v': 'Char ', 'V': 'Line ', '': 'Block '}
       let mode = dict.visual ? vmode[dict.visual] : vmode['V']
-      let winwidth = winwidth(0)
+      let winwidth = airline#util#winwidth()
       if winwidth < 80
         let mode = mode[0]
       endif

autoload/airline/extensions/po.vim

@@ -13,7 +13,7 @@ function! airline#extensions#po#shorten()
       let b:airline_po_stats = b:airline_po_stats[0:(w:displayed_po_limit - 2)].(&encoding==?'utf-8' ? '…' : '.'). ']'
     endif
   endif
-  if strlen(get(b:, 'airline_po_stats', '')) >= 30 && winwidth(0) < 150
+  if strlen(get(b:, 'airline_po_stats', '')) >= 30 && airline#util#winwidth() < 150
     let fuzzy = ''
     let untranslated = ''
     let messages = ''
@@ -35,8 +35,8 @@ endfunction
 
 function! airline#extensions#po#on_winenter()
   " only reset cache, if the window size changed
-  if get(b:, 'airline_winwidth', 0) != winwidth(0)
-    let b:airline_winwidth = winwidth(0)
+  if get(b:, 'airline_winwidth', 0) != airline#util#winwidth()
+    let b:airline_winwidth = airline#util#winwidth()
     " needs re-formatting
     unlet! b:airline_po_stats
   endif

autoload/airline/extensions/tabline.vim

@@ -33,6 +33,11 @@ function! s:toggle_off()
 endfunction
 
 function! s:toggle_on()
+  if get(g:, 'airline_statusline_ontop', 0)
+    call airline#extensions#tabline#enable()
+    let &tabline='%!airline#statusline('.winnr().')'
+    return
+  endif
   call airline#extensions#tabline#autoshow#on()
   call airline#extensions#tabline#tabs#on()
   call airline#extensions#tabline#buffers#on()
@@ -58,12 +63,25 @@ function! s:update_tabline()
     return
   endif
   call airline#util#doautocmd('BufMRUChange')
+  call airline#extensions#tabline#redraw()
+endfunction
+
+function! airline#extensions#tabline#redraw()
   " sometimes, the tabline is not correctly updated see #1580
   " so force redraw here
   if exists(":redrawtabline") == 2
     redrawtabline
   else
-    let &tabline = &tabline
+  " Have to set a property equal to itself to get airline to re-eval.
+  " Setting `let &tabline=&tabline` destroys the cursor position so we
+  " need something less invasive.
+    let &ro = &ro
+  endif
+endfunction
+
+function! airline#extensions#tabline#enable()
+  if &lines > 3
+    set showtabline=2
   endif
 endfunction
 

autoload/airline/extensions/tabline/autoshow.vim

@@ -24,9 +24,7 @@ function! airline#extensions#tabline#autoshow#on()
   augroup airline_tabline_autoshow
     autocmd!
     if s:buf_min_count <= 0 && s:tab_min_count <= 1
-      if &lines > 3
-        set showtabline=2
-      endif
+      call airline#extensions#tabline#enable()
     else
       if s:show_buffers == 1
         autocmd BufEnter  * call <sid>show_tabline(s:buf_min_count, len(airline#extensions#tabline#buflist#list()))

autoload/airline/extensions/wordcount/formatters/default.vim

@@ -24,7 +24,7 @@ else
 endif
 
 function! airline#extensions#wordcount#formatters#default#to_string(wordcount)
-  if winwidth(0) >= 80
+  if airline#util#winwidth() >= 80
     if a:wordcount > 999
       " Format number according to locale, e.g. German: 1.245 or English: 1,245
       let wordcount = substitute(a:wordcount, '\d\@<=\(\(\d\{3\}\)\+\)$', s:decimal_group.'&', 'g')