feat: v0.1 of extensions (#278)

lua/telescope/_extensions/init.lua

@@ -0,0 +1,62 @@
+local extensions = {}
+
+extensions._loaded = {}
+extensions._config = {}
+
+extensions.manager = setmetatable({}, {
+  __index = function(t, k)
+    -- See if this extension exists.
+    local ok, ext = pcall(require, 'telescope._extensions.' .. k)
+    if not ok then
+      error("This extenion doesn't exist or is not installed: " .. k .. "\n" .. ext)
+    end
+
+    if ext.setup then
+      ext.setup(extensions._config[k] or {}, require('telescope.config').values)
+    end
+
+    t[k] = ext.exports or {}
+
+    return t[k]
+  end,
+})
+
+--- Register an extension module.
+---
+--- Extensions have several important keys.
+---     - setup:
+---         function(ext_config, config) -> nil
+---
+---         Called when first loading the extension.
+---         The first parameter is the config passed by the user
+---             in telescope setup. The second parameter is the resulting
+---             config.values after applying the users setup defaults.
+---
+---         It is acceptable for a plugin to override values in config,
+---         as some plugins will be installed simply to manage some setup,
+---         install some sorter, etc.
+---
+---     - exports:
+---         table
+---
+---         Only the items in `exports` will be exposed on the  resulting
+---         module that users can access via require('telescope').extensions.foo
+---
+---         Other things in the module will not be accessible. This is the public API
+---         for your extension. Consider not breaking it a lot :laugh:
+---
+--- TODO:
+---     - actions
+extensions.register = function(mod)
+  return mod
+end
+
+extensions.load = function(name)
+  return extensions.manager[name]
+end
+
+extensions.set_config = function(extensions_config)
+  extensions._config = extensions_config or {}
+end
+
+return extensions