Go to the autoload function definition in VimL.
gf-autoload is a Vim plugin to extend gf and other commands.
With this plugin, you can open the file and locate the cursor to the function definition from the autoload function identifier under the cursor.
(Additional) the functionality of jumping to the script-local function definition is also provided.
Type gf on foo#bar() or s:foo() (<SID>foo()) function.