Allow configuring zoom, closes #189

autoload/tagbar.vim

@@ -1929,12 +1929,21 @@ endfunction
 " s:ZoomWindow() {{{2
 function! s:ZoomWindow() abort
     if s:is_maximized
-        execute 'vert resize ' . g:tagbar_width
+        execute 'vertical resize ' . g:tagbar_width
         execute s:winrestcmd
         let s:is_maximized = 0
     else
         let s:winrestcmd = winrestcmd()
-        vert resize
+        if g:tagbar_zoomwidth == 1
+            vertical resize
+        elseif g:tagbar_zoomwidth == 0
+            let func = exists('*strdisplaywidth') ? 'strdisplaywidth' : 'strlen'
+            let maxline = max(map(getline(line('w0'), line('w$')),
+                                \ func . '(v:val)'))
+            execute 'vertical resize ' . maxline
+        elseif g:tagbar_zoomwidth > 1
+            execute 'vertical resize ' . g:tagbar_zoomwidth
+        endif
         let s:is_maximized = 1
     endif
 endfunction

doc/tagbar.txt

@@ -398,6 +398,22 @@ Example:
         let g:tagbar_width = 30
 <
 
+                                                          *g:tagbar_zoomwidth*
+g:tagbar_zoomwidth~
+Default: 1
+
+Width of the Tagbar window when zoomed.
+
+Possible values are:
+  1: Use the maximum width available.
+  0: Use the width of the longest currently visible tag.
+  >1: Use this width in characters.
+
+Example:
+>
+        let g:tagbar_zoomwidth = 0
+<
+
                                                           *g:tagbar_autoclose*
 g:tagbar_autoclose~
 Default: 0

plugin/tagbar.vim

@@ -65,6 +65,7 @@ let s:options = [
     \ ['sort', 1],
     \ ['systemenc', &encoding],
     \ ['width', 40],
+    \ ['zoomwidth', 1],
 \ ]
 
 for [opt, val] in s:options