Build OTP tags and add to vim tags path

Author: NelsonVides

README.md

@@ -62,6 +62,27 @@ Or within Vim by executing the following command:
 Note that for the latter command, the current working directory will be used
 (`:help pwd` to find out more).
 
+### Generate OTP tags
+
+Often, you might be curious about the implementation of that function from the
+OTP libraries, but `CTRL-t` is not taking you there. We have a solution for
+this:
+
+    call AsyncBuildOtpTags()
+
+This command will find the path to your otp installation, and inside its `lib/`
+folder, it will build a tags file called `otptags`. The next thing you need, is
+to make vim aware of this. That's where the next function comes in place:
+
+    call GetOtpTagsPath()
+
+This will return the path to the generated `otptags` file, wherever this file
+lives. Extract it, and add it to your tags by doing
+
+    let &tags.="," . otptags_path
+
+Where otptags\_path is the expanded path returned previously.
+
 ### Options
 
 #### `g:erlang_tags_ignore`

plugin/vim-erlang-tags.vim

@@ -22,6 +22,7 @@ endif
 autocmd FileType erlang call VimErlangTagsDefineMappings()
 
 let s:exec_script = expand('<sfile>:p:h') . "/../bin/vim_erlang_tags.erl"
+let s:otppath_cmd = 'erl -noinput -eval ''io:format("~ts", [code:lib_dir()]), init:stop().'''
 
 function! s:GetExecuteCmd()
     let script_opts = ""
@@ -42,6 +43,17 @@ function! s:GetExecuteCmd()
     return s:exec_script . script_opts
 endfunction
 
+function! GetOtpTagsPath()
+    let otppath = system(s:otppath_cmd)
+    let otptags = otppath . "/otptags"
+    return otptags
+endfunction
+
+function! AsyncBuildOtpTags()
+    let cmd = '(OTPPATH=`' . s:otppath_cmd . '` && ' . s:exec_script . ' -i $OTPPATH -o $OTPPATH/otptags)'
+    call system(cmd . " &")
+endfunction
+
 function! VimErlangTags(...)
     let param = join(a:000, " ")
     let exec_cmd = s:GetExecuteCmd()
@@ -104,7 +116,7 @@ if !exists("s:os")
 endif
 
 " https://vim.fandom.com/wiki/Autocmd_to_update_ctags_file
-function! DelTagOfFile(file)
+function! s:DelTagOfFile(file)
   let fullpath = a:file
   let cwd = getcwd()
   let tagfilename = cwd . "/tags"