add hook after treesitter update

lua/plugins/treesitter.lua

@@ -1,3 +1,16 @@
+-- This hook checks for a treesitter update, verifies that the plugin
+-- is active and runs TSUpdate
+-- !! It needs to be defined before vim.pack.add to work
+vim.api.nvim_create_autocmd('PackChanged', {
+    callback = function(ev)
+        local name, kind = ev.data.spec.name, ev.data.kind
+        if name == 'nvim-treesitter' and kind == 'update' then
+            if not ev.data.active then vim.cmd.packadd('nvim-treesitter') end
+            vim.cmd('TSUpdate')
+        end
+    end
+})
+
 vim.pack.add({
     { src = 'https://github.com/nvim-treesitter/nvim-treesitter',             name = 'treesitter',            branch = 'main' },
     { src = 'https://github.com/nvim-treesitter/nvim-treesitter-context',     name = 'treesitter-context' },