diff --git a/lua/oil/adapters/files.lua b/lua/oil/adapters/files.lua
index ffc970d..a02a789 100644
--- a/lua/oil/adapters/files.lua
+++ b/lua/oil/adapters/files.lua
@@ -46,6 +46,7 @@ local file_columns = {}
 local fs_stat_meta_fields = {
   stat = function(parent_url, entry, cb)
     local _, path = util.parse_url(parent_url)
+    assert(path)
     local dir = fs.posix_to_os_path(path)
     vim.loop.fs_stat(fs.join(dir, entry[FIELD_NAME]), cb)
   end,
@@ -108,6 +109,7 @@ if not fs.is_windows then
 
     render_action = function(action)
       local _, path = util.parse_url(action.url)
+      assert(path)
       return string.format(
         "CHMOD %s %s",
         permissions.mode_to_octal_str(action.value),
@@ -117,11 +119,13 @@ if not fs.is_windows then
 
     perform_action = function(action, callback)
       local _, path = util.parse_url(action.url)
+      assert(path)
       path = fs.posix_to_os_path(path)
       vim.loop.fs_stat(path, function(err, stat)
         if err then
           return callback(err)
         end
+        assert(stat)
         -- We are only changing the lower 12 bits of the mode
         local mask = bit.bnot(bit.lshift(1, 12) - 1)
         local old_mode = bit.band(stat.mode, mask)
@@ -178,6 +182,7 @@ end
 ---@param callback fun(url: string)
 M.normalize_url = function(url, callback)
   local scheme, path = util.parse_url(url)
+  assert(path)
   local os_path = vim.fn.fnamemodify(fs.posix_to_os_path(path), ":p")
   vim.loop.fs_realpath(os_path, function(err, new_os_path)
     local realpath = new_os_path or os_path
@@ -210,6 +215,7 @@ end
 ---@param callback fun(err: nil|string, entries: nil|oil.InternalEntry[])
 M.list = function(url, column_defs, callback)
   local _, path = util.parse_url(url)
+  assert(path)
   local dir = fs.posix_to_os_path(path)
   local fetch_meta = columns.get_metadata_fetcher(M, column_defs)
   cache.begin_update_url(url)
@@ -300,6 +306,7 @@ end
 M.is_modifiable = function(bufnr)
   local bufname = vim.api.nvim_buf_get_name(bufnr)
   local _, path = util.parse_url(bufname)
+  assert(path)
   local dir = fs.posix_to_os_path(path)
   local stat = vim.loop.fs_stat(dir)
   if not stat then
@@ -329,6 +336,7 @@ end
 M.render_action = function(action)
   if action.type == "create" then
     local _, path = util.parse_url(action.url)
+    assert(path)
     local ret = string.format("CREATE %s", M.to_short_os_path(path, action.entry_type))
     if action.link then
       ret = ret .. " -> " .. fs.posix_to_os_path(action.link)
@@ -336,12 +344,15 @@ M.render_action = function(action)
     return ret
   elseif action.type == "delete" then
     local _, path = util.parse_url(action.url)
+    assert(path)
     return string.format("DELETE %s", M.to_short_os_path(path, action.entry_type))
   elseif action.type == "move" or action.type == "copy" then
     local dest_adapter = config.get_adapter_by_scheme(action.dest_url)
     if dest_adapter == M then
       local _, src_path = util.parse_url(action.src_url)
+      assert(src_path)
       local _, dest_path = util.parse_url(action.dest_url)
+      assert(dest_path)
       return string.format(
         "  %s %s -> %s",
         action.type:upper(),
@@ -362,6 +373,7 @@ end
 M.perform_action = function(action, cb)
   if action.type == "create" then
     local _, path = util.parse_url(action.url)
+    assert(path)
     path = fs.posix_to_os_path(path)
     if action.entry_type == "directory" then
       vim.loop.fs_mkdir(path, 493, function(err)
@@ -387,6 +399,7 @@ M.perform_action = function(action, cb)
     end
   elseif action.type == "delete" then
     local _, path = util.parse_url(action.url)
+    assert(path)
     path = fs.posix_to_os_path(path)
     if config.delete_to_trash then
       trash.recursive_delete(path, cb)
@@ -397,7 +410,9 @@ M.perform_action = function(action, cb)
     local dest_adapter = config.get_adapter_by_scheme(action.dest_url)
     if dest_adapter == M then
       local _, src_path = util.parse_url(action.src_url)
+      assert(src_path)
       local _, dest_path = util.parse_url(action.dest_url)
+      assert(dest_path)
       src_path = fs.posix_to_os_path(src_path)
       dest_path = fs.posix_to_os_path(dest_path)
       fs.recursive_move(action.entry_type, src_path, dest_path, vim.schedule_wrap(cb))
@@ -409,7 +424,9 @@ M.perform_action = function(action, cb)
     local dest_adapter = config.get_adapter_by_scheme(action.dest_url)
     if dest_adapter == M then
       local _, src_path = util.parse_url(action.src_url)
+      assert(src_path)
       local _, dest_path = util.parse_url(action.dest_url)
+      assert(dest_path)
       src_path = fs.posix_to_os_path(src_path)
       dest_path = fs.posix_to_os_path(dest_path)
       fs.recursive_copy(action.entry_type, src_path, dest_path, cb)
diff --git a/lua/oil/adapters/ssh.lua b/lua/oil/adapters/ssh.lua
index cc21051..fb87166 100644
--- a/lua/oil/adapters/ssh.lua
+++ b/lua/oil/adapters/ssh.lua
@@ -261,9 +261,11 @@ M.render_action = function(action)
     local dest = action.dest_url
     if config.get_adapter_by_scheme(src) == M then
       local _, path = util.parse_url(dest)
+      assert(path)
       dest = files.to_short_os_path(path, action.entry_type)
     else
       local _, path = util.parse_url(src)
+      assert(path)
       src = files.to_short_os_path(path, action.entry_type)
     end
     return string.format("  %s %s -> %s", action.type:upper(), src, dest)
@@ -328,9 +330,11 @@ M.perform_action = function(action, cb)
       if src_adapter == M then
         src_arg = url_to_scp(M.parse_url(action.src_url))
         local _, path = util.parse_url(action.dest_url)
+        assert(path)
         dest_arg = fs.posix_to_os_path(path)
       else
         local _, path = util.parse_url(action.src_url)
+        assert(path)
         src_arg = fs.posix_to_os_path(path)
         dest_arg = url_to_scp(M.parse_url(action.dest_url))
       end
@@ -353,7 +357,9 @@ M.read_file = function(bufnr)
   local tmpdir = fs.join(vim.fn.stdpath("cache"), "oil")
   fs.mkdirp(tmpdir)
   local fd, tmpfile = vim.loop.fs_mkstemp(fs.join(tmpdir, "ssh_XXXXXX"))
-  vim.loop.fs_close(fd)
+  if fd then
+    vim.loop.fs_close(fd)
+  end
   local tmp_bufnr = vim.fn.bufadd(tmpfile)
 
   shell.run({ "scp", "-C", scp_url, tmpfile }, function(err)
@@ -371,7 +377,10 @@ M.read_file = function(bufnr)
       vim.api.nvim_buf_set_lines(bufnr, 0, 1, true, {})
     end
     vim.bo[bufnr].modified = false
-    vim.bo[bufnr].filetype = vim.filetype.match({ buf = bufnr, filename = basename })
+    local filetype = vim.filetype.match({ buf = bufnr, filename = basename })
+    if filetype then
+      vim.bo[bufnr].filetype = filetype
+    end
     vim.cmd.doautocmd({ args = { "BufReadPost", bufname }, mods = { silent = true } })
     vim.api.nvim_buf_delete(tmp_bufnr, { force = true })
   end)
@@ -385,7 +394,9 @@ M.write_file = function(bufnr)
   local scp_url = url_to_scp(url)
   local tmpdir = fs.join(vim.fn.stdpath("cache"), "oil")
   local fd, tmpfile = vim.loop.fs_mkstemp(fs.join(tmpdir, "ssh_XXXXXXXX"))
-  vim.loop.fs_close(fd)
+  if fd then
+    vim.loop.fs_close(fd)
+  end
   vim.cmd.doautocmd({ args = { "BufWritePre", bufname }, mods = { silent = true } })
   vim.cmd.write({ args = { tmpfile }, bang = true, mods = { silent = true } })
   local tmp_bufnr = vim.fn.bufadd(tmpfile)
diff --git a/lua/oil/adapters/ssh/connection.lua b/lua/oil/adapters/ssh/connection.lua
index 8e592d0..3ebee70 100644
--- a/lua/oil/adapters/ssh/connection.lua
+++ b/lua/oil/adapters/ssh/connection.lua
@@ -3,6 +3,8 @@ local util = require("oil.util")
 
 ---@class oil.sshConnection
 ---@field meta {user?: string, groups?: string[]}
+---@field private term_bufnr integer
+---@field private jid integer
 local SSHConnection = {}
 
 local function output_extend(agg, output)
@@ -76,20 +78,21 @@ function SSHConnection.new(url)
     -- anything prior to that, it *will* appear. The first line gets swallowed.
     "echo '_make_newline_'; echo '===READY==='; exec /bin/bash --norc",
   })
+  local term_bufnr = vim.api.nvim_create_buf(false, true)
   local self = setmetatable({
     meta = {},
     commands = {},
     connected = false,
     connection_error = nil,
+    term_bufnr = term_bufnr,
   }, {
     __index = SSHConnection,
   })
 
-  self.term_bufnr = vim.api.nvim_create_buf(false, true)
   local term_id
   local mode = vim.api.nvim_get_mode().mode
-  util.run_in_fullscreen_win(self.term_bufnr, function()
-    term_id = vim.api.nvim_open_term(self.term_bufnr, {
+  util.run_in_fullscreen_win(term_bufnr, function()
+    term_id = vim.api.nvim_open_term(term_bufnr, {
       on_input = function(_, _, _, data)
         pcall(vim.api.nvim_chan_send, self.jid, data)
       end,
@@ -195,6 +198,7 @@ function SSHConnection:_handle_output(start_i)
     end
   else
     for i = start_i, #self._stdout - 1 do
+      ---@type string
       local line = self._stdout[i]
       if line:match("^===BEGIN===%s*$") then
         self._stdout = util.tbl_slice(self._stdout, i + 1)
diff --git a/lua/oil/adapters/test.lua b/lua/oil/adapters/test.lua
index b127dfc..0cd0eec 100644
--- a/lua/oil/adapters/test.lua
+++ b/lua/oil/adapters/test.lua
@@ -7,7 +7,7 @@ M.normalize_url = function(url, callback)
   callback(url)
 end
 
----@param path string
+---@param url string
 ---@param column_defs string[]
 ---@param cb fun(err: nil|string, entries: nil|oil.InternalEntry[])
 M.list = function(url, column_defs, cb)
diff --git a/lua/oil/cache.lua b/lua/oil/cache.lua
index da04b49..04d82eb 100644
--- a/lua/oil/cache.lua
+++ b/lua/oil/cache.lua
@@ -136,7 +136,7 @@ M.get_entry_by_url = function(url)
   return cache and cache[name]
 end
 
----@param oil.Action
+---@param action oil.Action
 M.perform_action = function(action)
   if action.type == "create" then
     local scheme, path = util.parse_url(action.url)
diff --git a/lua/oil/columns.lua b/lua/oil/columns.lua
index 43a4d14..625ecae 100644
--- a/lua/oil/columns.lua
+++ b/lua/oil/columns.lua
@@ -15,7 +15,10 @@ local all_columns = {}
 ---@class oil.ColumnDefinition
 ---@field render fun(entry: oil.InternalEntry, conf: nil|table): nil|oil.TextChunk
 ---@field parse fun(line: string, conf: nil|table): nil|string, nil|string
----@field meta_fields nil|table<string, fun(parent_url:L string, entry: oil.InternalEntry, cb: fn(err: nil|string))>
+---@field meta_fields nil|table<string, fun(parent_url: string, entry: oil.InternalEntry, cb: fun(err: nil|string))>
+---@field compare? fun(entry: oil.InternalEntry, parsed_value: any): boolean
+---@field render_action? fun(action: oil.ChangeAction): string
+---@field perform_action? fun(action: oil.ChangeAction, callback: fun(err: nil|string))
 
 ---@param name string
 ---@param column oil.ColumnDefinition
@@ -40,6 +43,7 @@ M.get_supported_columns = function(adapter_or_scheme)
   else
     adapter = adapter_or_scheme
   end
+  assert(adapter)
   local ret = {}
   for _, def in ipairs(config.columns) do
     if get_column(adapter, def) then
diff --git a/lua/oil/fs.lua b/lua/oil/fs.lua
index 7c9002a..ab6431b 100644
--- a/lua/oil/fs.lua
+++ b/lua/oil/fs.lua
@@ -31,6 +31,7 @@ M.touch = function(path, cb)
     if err then
       cb(err)
     else
+      assert(fd)
       vim.loop.fs_close(fd, cb)
     end
   end)
@@ -44,7 +45,8 @@ M.posix_to_os_path = function(path)
       local drive, rem = path:match("^/([^/]+)/(.*)$")
       return string.format("%s:\\%s", drive, rem:gsub("/", "\\"))
     else
-      return path:gsub("/", "\\")
+      local newpath = path:gsub("/", "\\")
+      return newpath
     end
   else
     return path
@@ -59,14 +61,15 @@ M.os_to_posix_path = function(path)
       local drive, rem = path:match("^([^:]+):\\(.*)$")
       return string.format("/%s/%s", drive:upper(), rem:gsub("\\", "/"))
     else
-      return path:gsub("\\", "/")
+      local newpath = path:gsub("\\", "/")
+      return newpath
     end
   else
     return path
   end
 end
 
-local home_dir = vim.loop.os_homedir()
+local home_dir = assert(vim.loop.os_homedir())
 
 ---@param path string
 ---@return string
@@ -189,7 +192,8 @@ M.recursive_copy = function(entry_type, src_path, dest_path, cb)
       if link_err then
         return cb(link_err)
       end
-      vim.loop.fs_symlink(link, dest_path, nil, cb)
+      assert(link)
+      vim.loop.fs_symlink(link, dest_path, 0, cb)
     end)
     return
   end
@@ -201,6 +205,7 @@ M.recursive_copy = function(entry_type, src_path, dest_path, cb)
     if stat_err then
       return cb(stat_err)
     end
+    assert(src_stat)
     vim.loop.fs_mkdir(dest_path, src_stat.mode, function(mkdir_err)
       if mkdir_err then
         return cb(mkdir_err)
diff --git a/lua/oil/init.lua b/lua/oil/init.lua
index ebe655e..ba16347 100644
--- a/lua/oil/init.lua
+++ b/lua/oil/init.lua
@@ -11,7 +11,7 @@ local M = {}
 
 ---@class oil.Adapter
 ---@field name string
----@field list fun(path: string, cb: fun(err: nil|string, entries: nil|oil.InternalEntry[]))
+---@field list fun(path: string, column_defs: string[], cb: fun(err: nil|string, entries: nil|oil.InternalEntry[]))
 ---@field is_modifiable fun(bufnr: integer): boolean
 ---@field get_column fun(name: string): nil|oil.ColumnDefinition
 ---@field normalize_url fun(url: string, callback: fun(url: string))
@@ -119,6 +119,7 @@ M.empty_trash = function()
     return
   end
   local _, path = util.parse_url(trash_url)
+  assert(path)
   local dir = fs.posix_to_os_path(path)
   if vim.fn.isdirectory(dir) == 1 then
     fs.recursive_delete("directory", dir, function(err)
@@ -157,6 +158,7 @@ M.get_current_dir = function()
   local util = require("oil.util")
   local scheme, path = util.parse_url(vim.api.nvim_buf_get_name(0))
   if config.adapters[scheme] == "files" then
+    assert(path)
     return fs.posix_to_os_path(path)
   end
 end
@@ -209,6 +211,7 @@ M.get_buffer_parent_url = function(bufname)
     local parent_url = util.addslash(scheme .. parent)
     return parent_url, basename
   else
+    assert(path)
     -- TODO maybe we should remove this special case and turn it into a config
     if scheme == "term://" then
       path = vim.fn.expand(path:match("^(.*)//"))
@@ -310,6 +313,7 @@ M.open_float = function(dir)
       local title = vim.api.nvim_buf_get_name(src_buf)
       local scheme, path = util.parse_url(title)
       if config.adapters[scheme] == "files" then
+        assert(path)
         local fs = require("oil.fs")
         title = vim.fn.fnamemodify(fs.posix_to_os_path(path), ":~")
       end
@@ -750,7 +754,7 @@ local function load_oil_buffer(bufnr)
     util.rename_buffer(bufnr, bufname)
   end
 
-  local adapter = config.get_adapter_by_scheme(scheme)
+  local adapter = assert(config.get_adapter_by_scheme(scheme))
 
   if vim.endswith(bufname, "/") then
     -- This is a small quality-of-life thing. If the buffer name ends with a `/`, we know it's a
@@ -885,6 +889,7 @@ M.setup = function(opts)
         vim.cmd.doautocmd({ args = { "BufWritePost", params.file }, mods = { silent = true } })
       else
         local adapter = config.get_adapter_by_scheme(bufname)
+        assert(adapter)
         adapter.write_file(params.buf)
       end
     end,
diff --git a/lua/oil/keymap_util.lua b/lua/oil/keymap_util.lua
index 3a582fd..42d09d7 100644
--- a/lua/oil/keymap_util.lua
+++ b/lua/oil/keymap_util.lua
@@ -5,7 +5,7 @@ local M = {}
 
 local function resolve(rhs)
   if type(rhs) == "string" and vim.startswith(rhs, "actions.") then
-    return resolve(actions[vim.split(rhs, ".", true)[2]])
+    return resolve(actions[vim.split(rhs, ".", { plain = true })[2]])
   elseif type(rhs) == "table" then
     local opts = vim.deepcopy(rhs)
     opts.callback = nil
diff --git a/lua/oil/loading.lua b/lua/oil/loading.lua
index 9ec6006..54a3cdd 100644
--- a/lua/oil/loading.lua
+++ b/lua/oil/loading.lua
@@ -16,7 +16,7 @@ local spinners = {
 }
 
 ---@param name_or_frames string|string[]
----@return fun()
+---@return fun(): string
 M.get_iter = function(name_or_frames)
   local frames
   if type(name_or_frames) == "string" then
diff --git a/lua/oil/mutator/init.lua b/lua/oil/mutator/init.lua
index cca4bcb..3aa0eb5 100644
--- a/lua/oil/mutator/init.lua
+++ b/lua/oil/mutator/init.lua
@@ -184,8 +184,9 @@ M.enforce_action_order = function(actions)
   --   a. TODO optimization: check immediate parents to see if they have no dependencies now
   -- 5. repeat
 
-  -- Gets the dependencies of a particular action. Effectively dynamically calculates the dependency
-  -- "edges" of the graph.
+  ---Gets the dependencies of a particular action. Effectively dynamically calculates the dependency
+  ---"edges" of the graph.
+  ---@param action oil.Action
   local function get_deps(action)
     local ret = {}
     if action.type == "delete" then
@@ -357,7 +358,9 @@ M.process_actions = function(actions, cb)
       if v.type == "delete" then
         local scheme, path = util.parse_url(v.url)
         if config.adapters[scheme] == "files" then
-          actions[i] = {
+          assert(path)
+          ---@type oil.MoveAction
+          local move_action = {
             type = "move",
             src_url = v.url,
             entry_type = v.entry_type,
@@ -366,6 +369,7 @@ M.process_actions = function(actions, cb)
               math.random(999999)
             ),
           }
+          actions[i] = move_action
         end
       end
     end
@@ -439,6 +443,7 @@ M.process_actions = function(actions, cb)
       end
     end)
     if action.type == "change" then
+      ---@cast action oil.ChangeAction
       columns.perform_change_action(adapter, action, callback)
     else
       adapter.perform_action(action, callback)
diff --git a/lua/oil/mutator/preview.lua b/lua/oil/mutator/preview.lua
index 54297e8..5e41898 100644
--- a/lua/oil/mutator/preview.lua
+++ b/lua/oil/mutator/preview.lua
@@ -76,6 +76,7 @@ M.show = vim.schedule_wrap(function(actions, should_confirm, cb)
     local adapter = util.get_adapter_for_action(action)
     local line
     if action.type == "change" then
+      ---@cast action oil.ChangeAction
       line = columns.render_change_action(adapter, action)
     else
       line = adapter.render_action(action)
diff --git a/lua/oil/mutator/progress.lua b/lua/oil/mutator/progress.lua
index d208c2d..d007150 100644
--- a/lua/oil/mutator/progress.lua
+++ b/lua/oil/mutator/progress.lua
@@ -169,6 +169,7 @@ function Progress:set_action(action, idx, total)
   local adapter = util.get_adapter_for_action(action)
   local change_line
   if action.type == "change" then
+    ---@cast action oil.ChangeAction
     change_line = columns.render_change_action(adapter, action)
   else
     change_line = adapter.render_action(action)
diff --git a/lua/oil/mutator/trie.lua b/lua/oil/mutator/trie.lua
index cb10bbd..85ec40e 100644
--- a/lua/oil/mutator/trie.lua
+++ b/lua/oil/mutator/trie.lua
@@ -1,6 +1,10 @@
 local util = require("oil.util")
+
+---@class oil.Trie
+---@field private root table
 local Trie = {}
 
+---@return oil.Trie
 Trie.new = function()
   return setmetatable({
     root = { values = {}, children = {} },
@@ -13,6 +17,7 @@ end
 ---@return string[]
 function Trie:_url_to_path_pieces(url)
   local scheme, path = util.parse_url(url)
+  assert(path)
   local pieces = vim.split(path, "/")
   table.insert(pieces, 1, scheme)
   return pieces
@@ -131,7 +136,7 @@ end
 ---Add all actions at a specific path
 ---@param url string
 ---@param ret oil.InternalEntry[]
----@param filter nil|fun(entry: oil.InternalEntry): boolean
+---@param filter? fun(entry: oil.InternalEntry): boolean
 function Trie:accum_actions_at(url, ret, filter)
   local pieces = self:_url_to_path_pieces(url)
   local current = self.root
diff --git a/lua/oil/util.lua b/lua/oil/util.lua
index ba3d140..dd2f5df 100644
--- a/lua/oil/util.lua
+++ b/lua/oil/util.lua
@@ -218,6 +218,7 @@ local function get_possible_buffer_names_from_url(url)
   local fs = require("oil.fs")
   local scheme, path = M.parse_url(url)
   if config.adapters[scheme] == "files" then
+    assert(path)
     return { fs.posix_to_os_path(path) }
   end
   return { url }
@@ -347,6 +348,7 @@ M.add_title_to_win = function(winid, opts)
     local title = vim.api.nvim_buf_get_name(src_buf)
     local scheme, path = M.parse_url(title)
     if config.adapters[scheme] == "files" then
+      assert(path)
       local fs = require("oil.fs")
       title = vim.fn.fnamemodify(fs.posix_to_os_path(path), ":~")
     end
@@ -456,7 +458,7 @@ M.get_adapter_for_action = function(action)
     error("no adapter found")
   end
   if action.dest_url then
-    local dest_adapter = config.get_adapter_by_scheme(action.dest_url)
+    local dest_adapter = assert(config.get_adapter_by_scheme(action.dest_url))
     if adapter ~= dest_adapter then
       if adapter.supports_xfer and adapter.supports_xfer[dest_adapter.name] then
         return adapter
diff --git a/lua/oil/view.lua b/lua/oil/view.lua
index e92587a..2342d37 100644
--- a/lua/oil/view.lua
+++ b/lua/oil/view.lua
@@ -476,6 +476,7 @@ M.format_entry_cols = function(entry, column_defs, col_width, adapter)
   for i, column in ipairs(column_defs) do
     local chunk = columns.render_col(adapter, column, entry)
     local text = type(chunk) == "table" and chunk[1] or chunk
+    ---@cast text string
     col_width[i + 1] = math.max(col_width[i + 1], vim.api.nvim_strwidth(text))
     table.insert(cols, chunk)
   end