Make auto_tags preserve existing tag section structure

autoload/vimwiki/tags.vim

@@ -360,22 +360,28 @@ function! vimwiki#tags#generate_tags(create, ...) abort
 
     " make a dictionary { tag_name: [tag_links, ...] }
     let tags_entries = {}
+    for tagname in self.specific_tags
+      let tags_entries[tagname] = []
+    endfor
+
     for entries in values(metadata)
       for entry in entries
         if has_key(tags_entries, entry.tagname)
           call add(tags_entries[entry.tagname], [entry.link, entry.description])
         else
+          if need_all_tags
             let tags_entries[entry.tagname] = [[entry.link, entry.description]]
           endif
+        endif
       endfor
       unlet entry " needed for older vims with sticky type checking since name is reused
     endfor
 
+    let tagnames = need_all_tags ? sort(keys(tags_entries)) : self.specific_tags
     let lines = []
     let bullet = repeat(' ', vimwiki#lst#get_list_margin()).vimwiki#lst#default_symbol().' '
     let current_dir = vimwiki#base#current_subdir()
-    for tagname in sort(keys(tags_entries))
-      if need_all_tags || index(self.specific_tags, tagname) != -1
+    for tagname in tagnames
       if len(lines) > 0
         call add(lines, '')
       endif
@@ -418,7 +424,6 @@ function! vimwiki#tags#generate_tags(create, ...) abort
           call add(lines, bullet . substitute(link_tpl, '__LinkUrl__', taglink, ''))
         endif
       endfor
-      endif
     endfor
 
     return lines

test/tag_update_existing_heading.vader

@@ -0,0 +1,63 @@
+# Test how vimwiki#tags#generate_tags behaves when updating existing tag link sections
+
+Before (Setup test wiki files):
+  call writefile([":usedtag:", ":othertag:"], expand("~/testmarkdown/Test-Tag-tagged.md"))
+  edit ~/testmarkdown/Test-Tag-links.md
+
+After (Cleanup files):
+  %delete
+  call system("rm $HOME/testmarkdown/.vimwiki_tags")
+  call system("rm $HOME/testmarkdown/Test-Tag-tagged.md")
+  call system("rm $HOME/testmarkdown/Test-Tag-links.md")
+
+
+Do (Create preexisting tag links with unused tag):
+  I
+  # Generated Tags\<CR>
+  \<CR>
+  ## unusedtag\<CR>
+  \<CR>
+  ## usedtag\<CR>
+  \<ESC>
+  :VimwikiRebuildTags!\<CR>
+  :call vimwiki#tags#generate_tags(0)\<CR>
+
+Expect (Keeps unused tag header):
+  # Generated Tags
+
+  ## unusedtag
+
+
+  ## usedtag
+
+  - [Test-Tag-tagged](Test-Tag-tagged)
+
+Do (Create preexisting tag subheadings out of alphabetical order):
+  I
+  # Generated Tags\<CR>
+  \<CR>
+  ## z\<CR>
+  \<CR>
+  ## usedtag\<CR>
+  \<CR>
+  ## a\<CR>
+  \<CR>
+  # Other Stuff
+  \<ESC>
+  :VimwikiRebuildTags!\<CR>
+  :call vimwiki#tags#generate_tags(0)\<CR>
+
+Expect (Existing tag subheading order is preserved):
+  # Generated Tags
+
+  ## z
+
+
+  ## usedtag
+
+  - [Test-Tag-tagged](Test-Tag-tagged)
+
+  ## a
+
+
+  # Other Stuff