make gtags.vim work for any dir

[Andrey Butirsky]

Hello,

Vim is capable to handle tags even if your current directory is not
within the project, because it can deal with the path of
the current file:
http://vimdoc.sourceforge.net/htmldoc/tagsrch.html#tags-option

I tried to achieve similar capability for GNU GLOBAL.
Here is what I've got:

--- /usr/share/gtags/gtags.vim  2018-07-19 08:25:46.000000000 +0300
+++ /home/bam/.vim/plugin/gtags.vim     2019-01-22 06:13:10.221680075 +0300
@@ -212,7 +212,7 @@
 "
 let s:global_command = $GTAGSGLOBAL
 if s:global_command == ''
-        let s:global_command = "global"
+        let s:global_command = "'cd ' . expand('%:h:S') . ' && global -a'"
 endif
 " Open the Gtags output window.  Set this variable to zero, to not open
 " the Gtags output window by default.  You can open it manually by using
@@ -400,7 +400,7 @@
     if l:isfile == 1
         let l:cmd = s:global_command . ' ' . l:option . ' ' .
g:Gtags_Shell_Quote_Char . a:pattern . g:Gtags_Shell_Quote_Char
     else
-        let l:cmd = s:global_command . ' ' . l:option . 'e ' .
g:Gtags_Shell_Quote_Char . a:pattern . g:Gtags_Shell_Quote_Char
+        exe 'let l:cmd =' s:global_command ". ' ' . l:option . 'e ' .
g:Gtags_Shell_Quote_Char . a:pattern . g:Gtags_Shell_Quote_Char"
     endif
 
     let l:result = system(l:cmd)


Would love to hear your suggestions/comments!