Add convenience function for automatically opening Tagbar

autoload/tagbar.vim

@@ -1390,7 +1390,7 @@ function! s:ToggleWindow()
         return
     endif
 
-    call s:OpenWindow(0)
+    call s:OpenWindow('')
 endfunction
 
 " s:OpenWindow() {{{2
@@ -2935,6 +2935,38 @@ function! s:CheckMouseClick()
     endif
 endfunction
 
+" s:DetermineFiletype() {{{2
+function! s:DetectFiletype(bufnr)
+    " Filetype has already been detected for loaded buffers, but not
+    " necessarily for unloaded ones
+    let ftype = getbufvar(a:bufnr, '&filetype')
+
+    if bufloaded(a:bufnr)
+        return ftype
+    endif
+
+    if ftype != ''
+        return ftype
+    endif
+
+    " Unloaded buffer with non-detected filetype, need to detect filetype
+    " manually
+    let bufname = bufname(a:bufnr)
+
+    let eventignore_save = &eventignore
+    set eventignore=FileType
+    let filetype_save = &filetype
+
+    exe 'doautocmd filetypedetect BufRead ' . bufname
+    let ftype = &filetype
+
+    let &filetype = filetype_save
+    let &eventignore = eventignore_save
+
+    return ftype
+endfunction
+
+
 " TagbarBalloonExpr() {{{2
 function! TagbarBalloonExpr()
     let taginfo = s:GetTagInfo(v:beval_lnum, 1)
@@ -3035,5 +3067,21 @@ function! tagbar#RestoreSession()
     call s:RestoreSession()
 endfunction
 
+" Automatically open Tagbar if one of the open buffers contains a supported
+" file
+function! tagbar#autoopen()
+    call s:Init()
+
+    for bufnr in range(1, bufnr('$'))
+        if buflisted(bufnr)
+            let ftype = s:DetectFiletype(bufnr)
+            if s:IsValidFile(bufname(bufnr), ftype)
+                call s:OpenWindow('')
+                return
+            endif
+        endif
+    endfor
+endfunction
+
 " Modeline {{{1
 " vim: ts=8 sw=4 sts=4 et foldenable foldmethod=marker foldcolumn=1

doc/tagbar.txt

@@ -536,19 +536,32 @@ See |:highlight| for more information.
 ------------------------------------------------------------------------------
 AUTOMATICALLY OPENING TAGBAR				*tagbar-autoopen*
 
-If you want Tagbar to open automatically, for example on Vim startup or for
-specific filetypes, there are various ways to do it. For example, to always
-open Tagbar on Vim startup you can put this into your vimrc file:
->
-    autocmd VimEnter * nested TagbarOpen
-<
-If you want to have it start for specific filetypes put
->
-    TagbarOpen
-<
-into a corresponding filetype plugin (see |filetype-plugin|).
+Since there are several different situations in which you might want to open
+Tagbar automatically there is no single option to enable automatic opening.
+Instead, autocommands can be used together with a convenience function that
+opens Tagbar only if a supported file is open(ed).
 
-Check out |autocmd.txt| if you want it to automatically open in more
+If you want to open Tagbar automatically on Vim startup no matter what put
+this into your vimrc:
+>
+    autocmd VimEnter * nested :TagbarOpen
+<
+If you want to open it only if you're opening Vim with a supported file/files
+use this instead:
+>
+    autocmd VimEnter * nested :call tagbar#autoopen()
+<
+For opening Tagbar also if you open a supported file in an already running
+Vim:
+>
+    autocmd FileType * nested :call tagbar#autoopen()
+<
+And if you only want to open Tagbar only for specific filetypes, not for all
+of the supported ones:
+>
+    autocmd FileType c,cpp nested :TagbarOpen
+<
+Check out |autocmd.txt| if you want it to open automatically in more
 complicated cases.
 
 ==============================================================================