neovim/runtime/lua/vim/_meta.lua

-- prevents luacheck from making lints for setting things on vim
local vim = assert(vim)

local a = vim.api
local validate = vim.validate

local SET_TYPES = setmetatable({
  SET    = 0,
  LOCAL  = 1,
  GLOBAL = 2,
}, { __index = error })

local options_info = {}
for _, v in pairs(a.nvim_get_all_options_info()) do
  options_info[v.name] = v
  if v.shortname ~= "" then options_info[v.shortname] = v end
end

local is_global_option = function(info) return info.scope == "global" end
local is_buffer_option = function(info) return info.scope == "buf" end
local is_window_option = function(info) return info.scope == "win" end

local get_scoped_options = function(scope)
  local result = {}
  for name, option_info in pairs(options_info) do
    if option_info.scope == scope then
      result[name] = true
    end
  end

  return result
end

local buf_options = get_scoped_options("buf")
local glb_options = get_scoped_options("global")
local win_options = get_scoped_options("win")

local function make_meta_accessor(get, set, del, validator)
  validator = validator or function() return true end

  validate {
    get = {get, 'f'};
    set = {set, 'f'};
    del = {del, 'f', true};
    validator = {validator, 'f'};
  }

  local mt = {}
  function mt:__newindex(k, v)
    if not validator(k) then
      return
    end

    if del and v == nil then
      return del(k)
    end
    return set(k, v)
  end
  function mt:__index(k)
    if not validator(k) then
      return
    end

    return get(k)
  end
  return setmetatable({}, mt)
end

vim.env = make_meta_accessor(function(k)
  local v = vim.fn.getenv(k)
  if v == vim.NIL then
    return nil
  end
  return v
end, vim.fn.setenv)

do -- buffer option accessor
  local function new_buf_opt_accessor(bufnr)
    local function get(k)
      if bufnr == nil and type(k) == "number" then
        return new_buf_opt_accessor(k)
      end

      return a.nvim_buf_get_option(bufnr or 0, k)
    end

    local function set(k, v)
      return a.nvim_buf_set_option(bufnr or 0, k, v)
    end

    return make_meta_accessor(get, set, nil, function(k)
      if type(k) == 'string' then
        if win_options[k] then
          error(string.format([['%s' is a window option, not a buffer option. See ":help %s"]], k, k))
        elseif glb_options[k] then
          error(string.format([['%s' is a global option, not a buffer option. See ":help %s"]], k, k))
        end
      end

      return true
    end)
  end

  vim.bo = new_buf_opt_accessor(nil)
end

do -- window option accessor
  local function new_win_opt_accessor(winnr)
    local function get(k)
      if winnr == nil and type(k) == "number" then
        return new_win_opt_accessor(k)
      end
      return a.nvim_win_get_option(winnr or 0, k)
    end

    local function set(k, v)
      return a.nvim_win_set_option(winnr or 0, k, v)
    end

    return make_meta_accessor(get, set, nil, function(k)
      if type(k) == 'string' then
        if buf_options[k] then
          error(string.format([['%s' is a buffer option, not a window option. See ":help %s"]], k, k))
        elseif glb_options[k] then
          error(string.format([['%s' is a global option, not a window option. See ":help %s"]], k, k))
        end
      end

      return true
    end)
  end

  vim.wo = new_win_opt_accessor(nil)
end

--[[
Local window setter

buffer options: does not get copied when split
  nvim_set_option(buf_opt, value) -> sets the default for NEW buffers
    this sets the hidden global default for buffer options

  nvim_buf_set_option(...) -> sets the local value for the buffer

  set opt=value, does BOTH global default AND buffer local value
  setlocal opt=value, does ONLY buffer local value

window options: gets copied
  does not need to call nvim_set_option because nobody knows what the heck this does⸮
  We call it anyway for more readable code.


    Command                 global value       local value
      :set option=value         set             set
 :setlocal option=value          -              set
:setglobal option=value         set              -
--]]
local function set_scoped_option(k, v, set_type)
  local info = options_info[k]

  -- Don't let people do setlocal with global options.
  --    That is a feature that doesn't make sense.
  if set_type == SET_TYPES.LOCAL and is_global_option(info) then
    error(string.format("Unable to setlocal option: '%s', which is a global option.", k))
  end

  -- Only `setlocal` skips setting the default/global value
  --    This will more-or-less noop for window options, but that's OK
  if set_type ~= SET_TYPES.LOCAL then
    a.nvim_set_option(k, v)
  end

  if is_window_option(info) then
    if set_type ~= SET_TYPES.GLOBAL then
      a.nvim_win_set_option(0, k, v)
    end
  elseif is_buffer_option(info) then
    if set_type == SET_TYPES.LOCAL
        or (set_type == SET_TYPES.SET and not info.global_local) then
      a.nvim_buf_set_option(0, k, v)
    end
  end
end

--[[
Local window getter

    Command                 global value       local value
      :set option?               -               display
 :setlocal option?               -               display
:setglobal option?              display             -
--]]
local function get_scoped_option(k, set_type)
  local info = assert(options_info[k], "Must be a valid option: " .. tostring(k))

  if set_type == SET_TYPES.GLOBAL or is_global_option(info) then
    return a.nvim_get_option(k)
  end

  if is_buffer_option(info) then
    local was_set, value = pcall(a.nvim_buf_get_option, 0, k)
    if was_set then return value end

    if info.global_local then
      return a.nvim_get_option(k)
    end

    error("buf_get: This should not be able to happen, given my understanding of options // " .. k)
  end

  if is_window_option(info) then
    local ok, value = pcall(a.nvim_win_get_option, 0, k)
    if ok then
      return value
    end

    local global_ok, global_val = pcall(a.nvim_get_option, k)
    if global_ok then
      return global_val
    end

    error("win_get: This should never happen. File an issue and tag @tjdevries")
  end

  error("This fallback case should not be possible. " .. k)
end

-- vim global option
--  this ONLY sets the global option. like `setglobal`
vim.go = make_meta_accessor(a.nvim_get_option, a.nvim_set_option)

-- vim `set` style options.
--  it has no additional metamethod magic.
vim.o = make_meta_accessor(
  function(k) return get_scoped_option(k, SET_TYPES.SET) end,
  function(k, v) return set_scoped_option(k, v, SET_TYPES.SET) end
)

---@brief [[
--- vim.opt, vim.opt_local and vim.opt_global implementation
---
--- To be used as helpers for working with options within neovim.
--- For information on how to use, see :help vim.opt
---
---@brief ]]

--- Preserves the order and does not mutate the original list
local remove_duplicate_values = function(t)
  local result, seen = {}, {}
  if type(t) == "function" then error(debug.traceback("asdf")) end
  for _, v in ipairs(t) do
    if not seen[v] then
      table.insert(result, v)
    end

    seen[v] = true
  end

  return result
end

-- TODO(tjdevries): Improve option metadata so that this doesn't have to be hardcoded.
--                  Can be done in a separate PR.
local key_value_options = {
  fillchars = true,
  listchars = true,
  winhl     = true,
}

---@class OptionType
--- Option Type Enum
local OptionTypes = setmetatable({
  BOOLEAN = 0,
  NUMBER  = 1,
  STRING  = 2,
  ARRAY   = 3,
  MAP     = 4,
  SET     = 5,
}, {
  __index = function(_, k) error("Not a valid OptionType: " .. k) end,
  __newindex = function(_, k) error("Cannot set a new OptionType: " .. k) end,
})

--- Convert a vimoption_T style dictionary to the correct OptionType associated with it.
---@return OptionType
local get_option_type = function(name, info)
  if info.type == "boolean" then
    return OptionTypes.BOOLEAN
  elseif info.type == "number" then
    return OptionTypes.NUMBER
  elseif info.type == "string" then
    if not info.commalist and not info.flaglist then
      return OptionTypes.STRING
    end

    if key_value_options[name] then
      assert(info.commalist, "Must be a comma list to use key:value style")
      return OptionTypes.MAP
    end

    if info.flaglist then
      return OptionTypes.SET
    elseif info.commalist then
      return OptionTypes.ARRAY
    end

    error("Fallthrough in OptionTypes")
  else
    error("Not a known info.type:" .. info.type)
  end
end


-- Check whether the OptionTypes is allowed for vim.opt
-- If it does not match, throw an error which indicates which option causes the error.
local function assert_valid_value(name, value, types)
  local type_of_value = type(value)
  for _, valid_type in ipairs(types) do
    if valid_type == type_of_value then
      return
    end
  end

  error(string.format("Invalid option type '%s' for '%s', should be %s", type_of_value, name, table.concat(types, " or ")))
end

local valid_types = {
  [OptionTypes.BOOLEAN] = { "boolean" },
  [OptionTypes.NUMBER]  = { "number" },
  [OptionTypes.STRING]  = { "string" },
  [OptionTypes.SET]     = { "string", "table" },
  [OptionTypes.ARRAY]   = { "string", "table" },
  [OptionTypes.MAP]     = { "string", "table" },
}

--- Convert a lua value to a vimoption_T value
local convert_value_to_vim = (function()
  -- Map of functions to take a Lua style value and convert to vimoption_T style value.
  -- Each function takes (info, lua_value) -> vim_value
  local to_vim_value = {
    [OptionTypes.BOOLEAN] = function(_, value) return value end,
    [OptionTypes.NUMBER] = function(_, value) return value end,
    [OptionTypes.STRING] = function(_, value) return value end,

    [OptionTypes.SET] = function(_, value)
      if type(value) == "string" then return value end
      local result = ''
      for k in pairs(value) do
        result = result .. k
      end

      return result
    end,

    [OptionTypes.ARRAY] = function(info, value)
      if type(value) == "string" then return value end
      if not info.allows_duplicates then
        value = remove_duplicate_values(value)
      end
      return table.concat(value, ",")
    end,

    [OptionTypes.MAP] = function(_, value)
      if type(value) == "string" then return value end

      local result = {}
      for opt_key, opt_value in pairs(value) do
        table.insert(result, string.format("%s:%s", opt_key, opt_value))
      end

      table.sort(result)
      return table.concat(result, ",")
    end,
  }

  return function(name, info, value)
    local option_type = get_option_type(name, info)
    assert_valid_value(name, value, valid_types[option_type])

    return to_vim_value[option_type](info, value)
  end
end)()

--- Converts a vimoption_T style value to a Lua value
local convert_value_to_lua = (function()
  -- Map of OptionType to functions that take vimoption_T values and conver to lua values.
  -- Each function takes (info, vim_value) -> lua_value
  local to_lua_value = {
    [OptionTypes.BOOLEAN] = function(_, value) return value end,
    [OptionTypes.NUMBER] = function(_, value) return value end,
    [OptionTypes.STRING] = function(_, value) return value end,

    [OptionTypes.ARRAY] = function(_, value)
      if type(value) == "table" then
        value = remove_duplicate_values(value)
        return value
      end

      return vim.split(value, ",")
    end,

    [OptionTypes.SET] = function(info, value)
      if type(value) == "table" then return value end

      assert(info.flaglist, "That is the only one I know how to handle")

      local result = {}
      for i = 1, #value do
        result[value:sub(i, i)] = true
      end

      return result
    end,

    [OptionTypes.MAP] = function(info, raw_value)
      if type(raw_value) == "table" then return raw_value end

      assert(info.commalist, "Only commas are supported currently")

      local result = {}

      local comma_split = vim.split(raw_value, ",")
      for _, key_value_str in ipairs(comma_split) do
        local key, value = unpack(vim.split(key_value_str, ":"))
        key = vim.trim(key)
        value = vim.trim(value)

        result[key] = value
      end

      return result
    end,
  }

  return function(name, info, option_value)
    return to_lua_value[get_option_type(name, info)](info, option_value)
  end
end)()

--- Handles the mutation of various different values.
local value_mutator = function(name, info, current, new, mutator)
  return mutator[get_option_type(name, info)](current, new)
end

--- Handles the '^' operator
local prepend_value = (function()
  local methods = {
    [OptionTypes.NUMBER] = function()
      error("The '^' operator is not currently supported for")
    end,

    [OptionTypes.STRING] = function(left, right)
      return right .. left
    end,

    [OptionTypes.ARRAY] = function(left, right)
      for i = #right, 1, -1 do
        table.insert(left, 1, right[i])
      end

      return left
    end,

    [OptionTypes.MAP] = function(left, right)
      return vim.tbl_extend("force", left, right)
    end,

    [OptionTypes.SET] = function(left, right)
      return vim.tbl_extend("force", left, right)
    end,
  }

  return function(name, info, current, new)
    return value_mutator(
      name, info, convert_value_to_lua(name, info, current), convert_value_to_lua(name, info, new), methods
    )
  end
end)()

--- Handles the '+' operator
local add_value = (function()
  local methods = {
    [OptionTypes.NUMBER] = function(left, right)
      return left + right
    end,

    [OptionTypes.STRING] = function(left, right)
      return left .. right
    end,

    [OptionTypes.ARRAY] = function(left, right)
      for _, v in ipairs(right) do
        table.insert(left, v)
      end

      return left
    end,

    [OptionTypes.MAP] = function(left, right)
      return vim.tbl_extend("force", left, right)
    end,

    [OptionTypes.SET] = function(left, right)
      return vim.tbl_extend("force", left, right)
    end,
  }

  return function(name, info, current, new)
    return value_mutator(
      name, info, convert_value_to_lua(name, info, current), convert_value_to_lua(name, info, new), methods
    )
  end
end)()

--- Handles the '-' operator
local remove_value = (function()
  local remove_one_item = function(t, val)
    if vim.tbl_islist(t) then
      local remove_index = nil
      for i, v in ipairs(t) do
        if v == val then
          remove_index = i
        end
      end

      if remove_index then
        table.remove(t, remove_index)
      end
    else
      t[val] = nil
    end
  end

  local methods = {
    [OptionTypes.NUMBER] = function(left, right)
      return left - right
    end,

    [OptionTypes.STRING] = function()
      error("Subtraction not supported for strings.")
    end,

    [OptionTypes.ARRAY] = function(left, right)
      if type(right) == "string" then
        remove_one_item(left, right)
      else
        for _, v in ipairs(right) do
          remove_one_item(left, v)
        end
      end

      return left
    end,

    [OptionTypes.MAP] = function(left, right)
      if type(right) == "string" then
        left[right] = nil
      else
        for _, v in ipairs(right) do
          left[v] = nil
        end
      end

      return left
    end,

    [OptionTypes.SET] = function(left, right)
      if type(right) == "string" then
        left[right] = nil
      else
        for _, v in ipairs(right) do
          left[v] = nil
        end
      end

      return left
    end,
  }

  return function(name, info, current, new)
    return value_mutator(name, info, convert_value_to_lua(name, info, current), new, methods)
  end
end)()

local create_option_metatable = function(set_type)
  local set_mt, option_mt

  local make_option = function(name, value)
    local info = assert(options_info[name], "Not a valid option name: " .. name)

    if type(value) == "table" and getmetatable(value) == option_mt then
      assert(name == value._name, "must be the same value, otherwise that's weird.")

      value = value._value
    end

    return setmetatable({
      _name = name,
      _value = value,
      _info = info,
    }, option_mt)
  end

  -- TODO(tjdevries): consider supporting `nil` for set to remove the local option.
  --                  vim.cmd [[set option<]]

  option_mt = {
    -- To set a value, instead use:
    --  opt[my_option] = value
    _set = function(self)
      local value = convert_value_to_vim(self._name, self._info, self._value)
      set_scoped_option(self._name, value, set_type)

      return self
    end,

    get = function(self)
      return convert_value_to_lua(self._name, self._info, self._value)
    end,

    append = function(self, right)
      return self:__add(right):_set()
    end,

    __add = function(self, right)
      return make_option(self._name, add_value(self._name, self._info, self._value, right))
    end,

    prepend = function(self, right)
      return self:__pow(right):_set()
    end,

    __pow = function(self, right)
      return make_option(self._name, prepend_value(self._name, self._info, self._value, right))
    end,

    remove = function(self, right)
      return self:__sub(right):_set()
    end,

    __sub = function(self, right)
      return make_option(self._name, remove_value(self._name, self._info, self._value, right))
    end
  }
  option_mt.__index = option_mt

  set_mt = {
    __index = function(_, k)
      return make_option(k, get_scoped_option(k, set_type))
    end,

    __newindex = function(_, k, v)
      local opt = make_option(k, v)
      opt:_set()
    end,
  }

  return set_mt
end

vim.opt = setmetatable({}, create_option_metatable(SET_TYPES.SET))
vim.opt_local = setmetatable({}, create_option_metatable(SET_TYPES.LOCAL))
vim.opt_global = setmetatable({}, create_option_metatable(SET_TYPES.GLOBAL))