scrollbar: add an ascii scrollbar extension

autoload/airline/extensions.vim

@@ -262,6 +262,11 @@ function! airline#extensions#load()
     call add(s:loaded_ext, 'bookmark')
   endif
 
+  if get(g:, 'airline#extensions#scrollbar#enabled', 1)
+    call airline#extensions#scrollbar#init(s:ext)
+    call add(s:loaded_ext, 'scrollbar')
+  endif
+
   if get(g:, 'airline#extensions#csv#enabled', 1)
         \ && (get(g:, 'loaded_csv', 0) || exists(':Table'))
     call airline#extensions#csv#init(s:ext)

autoload/airline/extensions/scrollbar.vim

@@ -0,0 +1,36 @@
+" MIT License. Copyright (c) 2013-2021
+" vim: et ts=2 sts=2 sw=2 et
+
+scriptencoding utf-8
+
+function! airline#extensions#scrollbar#calculate() abort
+  if winwidth(0) > 200 && get(w:, 'airline_active', 0)
+    let overwrite = 0
+    if &encoding ==? 'utf-8' && !get(g:, 'airline_symbols_ascii', 0)
+      let [left, right, middle] = [ '|', '|', '█']
+      let overwrite = 1
+    else
+      let [left, right, middle] = [ '[', ']', '-']
+    endif
+    let spc = get(g:, 'airline_symbols.space', ' ')
+    let width = 20 " max width, plus one border and indicator
+    let perc = (line('.') + 0.0) / (line('$') + 0.0)
+    let before = float2nr(round(perc * width))
+    if before > 0 && line('.') == 1
+      let before = 0
+      let left = (overwrite ? '' : left)
+    endif
+    let after  = width - before
+    if (after <= 1 && line('.') == line('$'))
+      let after = 0
+      let right = (overwrite ? '' : right)
+    endif
+    return left . repeat(spc,  before) . middle . repeat(spc, (width-before)) . right
+  else
+    return ''
+  endif
+endfunction
+
+function! airline#extensions#scrollbar#init(ext) abort
+  call airline#parts#define_function('scrollbar', 'airline#extensions#scrollbar#calculate')
+endfunction

autoload/airline/init.vim

@@ -186,10 +186,11 @@ function! airline#init#bootstrap()
         \ 'syntastic-err', 'eclim', 'whitespace','windowswap',
         \ 'ycm_error_count', 'ycm_warning_count', 'neomake_error_count',
         \ 'neomake_warning_count', 'ale_error_count', 'ale_warning_count',
-        \ 'lsp_error_count', 'lsp_warning_count',
+        \ 'lsp_error_count', 'lsp_warning_count', 'scrollbar',
         \ 'nvimlsp_error_count', 'nvimlsp_warning_count',
         \ 'languageclient_error_count', 'languageclient_warning_count',
         \ 'coc_warning_count', 'coc_error_count', 'vista', 'battery'])
+
   call airline#parts#define_text('bookmark', '')
   call airline#parts#define_text('capslock', '')
   call airline#parts#define_text('gutentags', '')
@@ -225,7 +226,7 @@ function! airline#init#sections()
     let g:airline_section_gutter = airline#section#create(['%='])
   endif
   if !exists('g:airline_section_x')
-    let g:airline_section_x = airline#section#create_right(['coc_current_function', 'bookmark', 'tagbar', 'vista', 'gutentags', 'gen_tags', 'omnisharp', 'grepper', 'filetype'])
+    let g:airline_section_x = airline#section#create_right(['coc_current_function', 'bookmark', 'scrollbar', 'tagbar', 'vista', 'gutentags', 'gen_tags', 'omnisharp', 'grepper', 'filetype'])
   endif
   if !exists('g:airline_section_y')
     let g:airline_section_y = airline#section#create_right(['ffenc'])