fix: builtin only have entries for extension functions (#1587)

* fix: `builtin` only have entries for extension functions

* fix: add check for underscore and explanation of which functions included

lua/telescope/_extensions/init.lua

@@ -43,6 +43,9 @@ extensions.manager = setmetatable({}, {
 ---
 ---         Only the items in `exports` will be exposed on the  resulting
 ---         module that users can access via require('telescope').extensions.foo
+---         Also, any top-level key-value pairs in exports where the value is a function and the
+---         key doesn't start with an underscore will be included when calling the `builtin` picker
+---         with the `include_extensions` option enabled.
 ---
 ---         Other things in the module will not be accessible. This is the public API
 ---         for your extension. Consider not breaking it a lot :laugh:

lua/telescope/builtin/internal.lua

@@ -55,6 +55,8 @@ internal.builtin = function(opts)
     title = "Telescope Pickers"
     for ext, funcs in pairs(require("telescope").extensions) do
       for func_name, func_obj in pairs(funcs) do
+        -- Only include exported functions whose name doesn't begin with an underscore
+        if type(func_obj) == "function" and string.sub(func_name, 0, 1) ~= "_" then
           local debug_info = debug.getinfo(func_obj)
           table.insert(objs, {
             filename = string.sub(debug_info.source, 2),
@@ -63,6 +65,7 @@ internal.builtin = function(opts)
         end
       end
     end
+  end
 
   pickers.new(opts, {
     prompt_title = title,