Move some tests to autoload

autoload/tagbar.vim

@@ -18,10 +18,53 @@
 "              use of this software.
 " ============================================================================
 
+scriptencoding utf-8
+
 " Initialization {{{1
 
 " Basic init {{{2
 
+if v:version < 700
+    echomsg 'Tagbar: Vim version is too old, Tagbar requires at least 7.0'
+    finish
+endif
+
+if !exists('g:tagbar_ctags_bin')
+    if executable('ctags-exuberant')
+        let g:tagbar_ctags_bin = 'ctags-exuberant'
+    elseif executable('exuberant-ctags')
+        let g:tagbar_ctags_bin = 'exuberant-ctags'
+    elseif executable('exctags')
+        let g:tagbar_ctags_bin = 'exctags'
+    elseif executable('ctags')
+        let g:tagbar_ctags_bin = 'ctags'
+    elseif executable('ctags.exe')
+        let g:tagbar_ctags_bin = 'ctags.exe'
+    elseif executable('tags')
+        let g:tagbar_ctags_bin = 'tags'
+    else
+        echomsg 'Tagbar: Exuberant ctags not found, skipping plugin'
+        finish
+    endif
+else
+    let g:tagbar_ctags_bin = expand(g:tagbar_ctags_bin)
+    if !executable(g:tagbar_ctags_bin)
+        echomsg 'Tagbar: Exuberant ctags not found in specified place,'
+              \ 'skipping plugin'
+        finish
+    endif
+endif
+
+redir => s:ftype_out
+silent filetype
+redir END
+if s:ftype_out !~# 'detection:ON'
+    echomsg 'Tagbar: Filetype detection is turned off, skipping plugin'
+    unlet s:ftype_out
+    finish
+endif
+unlet s:ftype_out
+
 if has('multi_byte') && has('unix') && &encoding == 'utf-8' &&
  \ (empty(&termencoding) || &termencoding == 'utf-8')
     let s:icon_closed = '▶'
@@ -45,6 +88,8 @@ let s:access_symbols = {
     \ 'private'   : '-'
 \ }
 
+let g:loaded_tagbar = 1
+
 " s:InitTypes() {{{2
 function! s:InitTypes()
     let s:known_types = {}
@@ -2782,4 +2827,4 @@ function! tagbar#RestoreSession()
 endfunction
 
 " Modeline {{{1
-" vim: ts=8 sw=4 sts=4 et foldenable foldmethod=marker foldcolumn=1
+" vim: ts=8 sw=4 sts=4 et foldenable foldmethod=marker foldcolumn=1