whitespace: support multiline statusline for warnings

Add a new airline_section_warning2 that displays whitespace warnings on
a second statusline line when Vim supports the statuslineopt option
(Vim 9.2.0083+) and g:airline_multiline is set. The second line only
appears when there are actual whitespace issues, avoiding an empty
second line when the buffer is clean.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

autoload/airline.vim

@@ -6,7 +6,7 @@ scriptencoding utf-8
 let g:airline_statusline_funcrefs = get(g:, 'airline_statusline_funcrefs', [])
 let g:airline_inactive_funcrefs = get(g:, 'airline_inactive_statusline_funcrefs', [])
 
-let s:sections = ['a','b','c','gutter','x','y','z', 'error', 'warning']
+let s:sections = ['a','b','c','gutter','x','y','z', 'error', 'warning', 'warning2']
 let s:contexts = {}
 let s:core_funcrefs = [
       \ function('airline#extensions#apply'),

autoload/airline/extensions/default.vim

@@ -11,10 +11,11 @@ let s:section_truncate_width = get(g:, 'airline#extensions#default#section_trunc
       \ 'z': 45,
       \ 'warning': 80,
       \ 'error': 80,
+      \ 'warning2': 80,
       \ })
 let s:layout = get(g:, 'airline#extensions#default#layout', [
       \ [ 'a', 'b', 'c' ],
-      \ [ 'x', 'y', 'z', 'warning', 'error' ]
+      \ [ 'x', 'y', 'z', 'warning', 'error', 'warning2' ]
       \ ])
 
 function! s:get_section(winnr, key, ...)
@@ -32,9 +33,24 @@ function! s:get_section(winnr, key, ...)
   return empty(text) ? '' : prefix.text.suffix
 endfunction
 
+function! s:eval_section_empty(content)
+  let exprlist = []
+  call substitute(a:content, '%{\([^}]*\)}', '\=add(exprlist, submatch(1))', 'g')
+  for expr in exprlist
+    try
+      if !empty(eval(expr))
+        return 0
+      endif
+    catch
+      return 0
+    endtry
+  endfor
+  return 1
+endfunction
+
 function! s:build_sections(builder, context, keys)
   for key in a:keys
-    if (key == 'warning' || key == 'error') && !a:context.active
+    if (key == 'warning' || key == 'error' || key == 'warning2') && !a:context.active
       continue
     endif
     call s:add_section(a:builder, a:context, key)
@@ -49,21 +65,30 @@ if s:section_use_groups && (v:version >= 704 || (v:version >= 703 && has('patch8
           \ (v:version == 704 && !has("patch1511"))
     " i have no idea why the warning section needs special treatment, but it's
     " needed to prevent separators from showing up
-    if ((a:key == 'error' || a:key == 'warning') && empty(s:get_section(a:context.winnr, a:key)))
+    if ((a:key == 'error' || a:key == 'warning' || a:key == 'warning2')
+          \ && empty(s:get_section(a:context.winnr, a:key)))
       return
     endif
-    if condition
-      call a:builder.add_raw('%(')
-    endif
-    call a:builder.add_section('airline_'.a:key, s:get_section(a:context.winnr, a:key))
-    if condition
-      call a:builder.add_raw('%)')
+    if a:key == 'warning2' && airline#util#has_multiline()
+      let section = s:get_section(a:context.winnr, a:key)
+      if !s:eval_section_empty(section)
+        call a:builder.add_raw('%@%#airline_warning#'.section)
+      endif
+    else
+      if condition
+        call a:builder.add_raw('%(')
+      endif
+      call a:builder.add_section('airline_'.a:key, s:get_section(a:context.winnr, a:key))
+      if condition
+        call a:builder.add_raw('%)')
+      endif
     endif
   endfunction
 else
   " older version don't like the use of %(%)
   function! s:add_section(builder, context, key)
-    if ((a:key == 'error' || a:key == 'warning') && empty(s:get_section(a:context.winnr, a:key)))
+    if ((a:key == 'error' || a:key == 'warning')
+          \ && empty(s:get_section(a:context.winnr, a:key)))
       return
     endif
     if a:key == 'warning'

autoload/airline/extensions/whitespace.vim

@@ -161,6 +161,9 @@ function! airline#extensions#whitespace#check()
       endif
     endif
   endif
+  if airline#util#has_multiline()
+    return b:airline_whitespace_check
+  endif
   return airline#util#shorten(b:airline_whitespace_check, 120, 9)
 endfunction
 
@@ -178,8 +181,16 @@ function! airline#extensions#whitespace#toggle()
 
   if exists("g:airline#extensions#whitespace#enabled")
     let g:airline#extensions#whitespace#enabled = s:enabled
-    if s:enabled && match(g:airline_section_warning, '#whitespace#check') < 0
-      let g:airline_section_warning .= airline#section#create(['whitespace'])
+    if s:enabled
+      if airline#util#has_multiline() && exists('g:airline_section_warning2')
+        if match(g:airline_section_warning2, '#whitespace#check') < 0
+          let g:airline_section_warning2 .= airline#section#create(['whitespace'])
+        endif
+      else
+        if match(g:airline_section_warning, '#whitespace#check') < 0
+          let g:airline_section_warning .= airline#section#create(['whitespace'])
+        endif
+      endif
       call airline#update_statusline()
     endif
   endif
@@ -211,7 +222,7 @@ function! s:ws_refresh()
     return
   endif
   unlet! b:airline_whitespace_check
-  if get(g:, 'airline_skip_empty_sections', 0)
+  if get(g:, 'airline_skip_empty_sections', 0) || airline#util#has_multiline()
     exe ':AirlineRefresh!'
   endif
   let b:airline_ws_changedtick = b:changedtick

autoload/airline/init.vim

@@ -294,7 +294,16 @@ function! airline#init#sections()
   if !exists('g:airline_section_error')
     let g:airline_section_error = airline#section#create(['ycm_error_count', 'syntastic-err', 'eclim', 'neomake_error_count', 'ale_error_count', 'lsp_error_count', 'nvimlsp_error_count', 'languageclient_error_count', 'coc_error_count', 'vim9lsp_error_count'])
   endif
-  if !exists('g:airline_section_warning')
-    let g:airline_section_warning = airline#section#create(['ycm_warning_count',  'syntastic-warn', 'neomake_warning_count', 'ale_warning_count', 'lsp_warning_count', 'nvimlsp_warning_count', 'languageclient_warning_count', 'whitespace', 'coc_warning_count', 'vim9lsp_warning_count'])
+  if airline#util#has_multiline()
+    if !exists('g:airline_section_warning')
+      let g:airline_section_warning = airline#section#create(['ycm_warning_count',  'syntastic-warn', 'neomake_warning_count', 'ale_warning_count', 'lsp_warning_count', 'nvimlsp_warning_count', 'languageclient_warning_count', 'coc_warning_count', 'vim9lsp_warning_count'])
+    endif
+    if !exists('g:airline_section_warning2')
+      let g:airline_section_warning2 = airline#section#create(['whitespace'])
+    endif
+  else
+    if !exists('g:airline_section_warning')
+      let g:airline_section_warning = airline#section#create(['ycm_warning_count',  'syntastic-warn', 'neomake_warning_count', 'ale_warning_count', 'lsp_warning_count', 'nvimlsp_warning_count', 'languageclient_warning_count', 'whitespace', 'coc_warning_count', 'vim9lsp_warning_count'])
+    endif
   endif
 endfunction

autoload/airline/util.vim

@@ -250,3 +250,9 @@ function! airline#util#has_vim9_script()
     \ get(g:, "airline_experimental", 0))
 endfunction
 
+function! airline#util#has_multiline()
+  " Returns true, if Vim supports multiline statusline (Vim 9.2.0083)
+  return (exists("+statuslineopt") &&
+    \ get(g:, "airline_multiline", 0))
+endfunction
+

doc/airline.txt

@@ -57,6 +57,8 @@ this: >
 +---------------------------------------------------------------------------+
 | A | B |                     C                          X | Y | Z |  [...] |
 +---------------------------------------------------------------------------+
+| [...]                                                                     |
++---------------------------------------------------------------------------+
 
 The statusline is the colored line at the bottom, which contains the sections
 (possibly in different colors):
@@ -82,6 +84,7 @@ section  meaning (example)~
 <
   [...]  additional sections (warning/errors/statistics)
          from external plugins (e.g. YCM/syntastic/...)
+         Can be shown on a second line optionally.
 
 For a better look, those sections can be colored differently, depending on
 the mode and whether the current file is 'modified'
@@ -124,6 +127,9 @@ values):
   " Currently: Enable Vim9 Script implementation
   let g:airline_experimental = 1
 
+* enable multiline feature (requires Vim 9.2.0083) >
+  let g:airline_multiline = 1
+
 * the separator used on the left side >
   let g:airline_left_sep='>'
 <
@@ -445,6 +451,7 @@ window.
                                  languageclient_error_count)
   let g:airline_section_warning (ycm_warning_count, syntastic-warn,
                                  languageclient_warning_count, whitespace)
+  let g:airline_section_warning2 (whitespace) [optional]
 
   " [*] This section needs at least the fugitive extension or else
   "     it will remain empty

plugin/airline.vim

@@ -203,6 +203,9 @@ function! s:airline_toggle()
         endif
       endif
     endif
+    if airline#util#has_multiline() && &statuslineopt !~ 'maxheight:'
+      set statuslineopt+=maxheight:2
+    endif
     if s:airline_initialized
       call s:on_window_changed('Init')
     endif