cache.lua: add type anotations for function and cache

modules/cache.lua

@@ -9,6 +9,10 @@ local utils = require 'mp.utils'
 local g = require 'modules.globals'
 local fb_utils = require 'modules.utils'
 
+---Returns an array of keys in a table.
+---@generic T
+---@param t table<T,any>
+---@return T[]
 local function get_keys(t)
     local keys = {}
     for key in pairs(t) do
@@ -17,6 +21,15 @@ local function get_keys(t)
     return keys
 end
 
+---@class CacheRef
+---@field directory string
+---@field ref State?
+
+---@class Cache
+---@field traversal_stack CacheRef[]
+---@field history CacheRef[]
+---@field cache table<string,State>
+---@field dangling_refs Set<string>
 local cache = {
     cache = setmetatable({}, {__mode = 'kv'}),
     traversal_stack = {},
@@ -41,16 +54,18 @@ function cache:print_debug_info()
     msg.debug(utils.to_string(fb_utils.list.map(self.history, function(ref) return ref.directory end)))
 end
 
-function cache:replace_dangling_refs(directory, ref)
+---@param directory string
+---@param state State
+function cache:replace_dangling_refs(directory, state)
     for _, v in ipairs(self.traversal_stack) do
         if v.directory == directory then
-            v.ref = ref
+            v.ref = state
             self.dangling_refs[directory] = nil
         end
     end
     for _, v in ipairs(self.history) do
         if v.directory == directory then
-            v.ref = ref
+            v.ref = state
             self.dangling_refs[directory] = nil
         end
     end
@@ -71,8 +86,10 @@ function cache:add_current_state()
     end
 end
 
--- Creates a reference to the cache of a particular directory to prevent it
--- from being garbage collected.
+---Creates a reference to the cache of a particular directory to prevent it
+---from being garbage collected.
+---@param directory string
+---@return CacheRef
 function cache:get_cache_ref(directory)
    return {
         directory = directory,
@@ -91,10 +108,14 @@ function cache:append_history()
     if (history_size + 1) > 100 then table.remove(self.history, 1) end
 end
 
+---@param directory string
+---@return boolean
 function cache:in_cache(directory)
     return self.cache[directory] ~= nil
 end
 
+---@param directory string
+---@return boolean
 function cache:apply(directory)
     directory = directory or g.state.directory
     local t = self.cache[directory]