Implement :VimwikiSearchTags to look up tag instances in a wiki

autoload/vimwiki/base.vim

@@ -2109,6 +2109,15 @@ endfunction " }}}
 
 " Command completion functions {{{
 
+" vimwiki#base#complete_tags
+function! vimwiki#base#complete_tags(ArgLead, CmdLine, CursorPos) abort " {{{
+  " We can safely ignore args if we use -custom=complete option, Vim engine
+  " will do the job of filtering.
+  let metadata = vimwiki#base#load_tags_metadata()
+  let taglist = vimwiki#base#get_tags(metadata)
+  return join(taglist, "\n")
+endfunction " }}}
+
 " vimwiki#base#complete_links_escaped
 function! vimwiki#base#complete_links_escaped(ArgLead, CmdLine, CursorPos) abort " {{{
   " We can safely ignore args if we use -custom=complete option, Vim engine

doc/vimwiki.txt

@@ -708,6 +708,10 @@ il                      A single list item.
     Iterates over all files in a current wiki and rebuilds tags metadata (to
     enable tags related commands).
 
+*:VimwikiSearchTags*
+    Searches over the pages in current wiki and finds all locations of a given
+    tag.  Supports |cmdline-completion|.
+
 ==============================================================================
 5. Wiki syntax                                                *vimwiki-syntax*
 

ftplugin/vimwiki.vim

@@ -304,6 +304,8 @@ command! -buffer VimwikiDiaryPrevDay call vimwiki#diary#goto_prev_day()
 
 " tags commands
 command! -buffer VimwikiRebuildTags call vimwiki#base#update_tags(1)
+command! -buffer -nargs=* -complete=custom,vimwiki#base#complete_tags
+      \ VimwikiSearchTags VimwikiSearch /:<args>:/
 
 " COMMANDS }}}