diff --git a/MAINTAIN.md b/MAINTAIN.md
index 927ddea5a1..2f936c8a00 100644
--- a/MAINTAIN.md
+++ b/MAINTAIN.md
@@ -87,6 +87,7 @@ These dependencies are "vendored" (inlined), we need to update the sources manua
   - [xdiff](https://github.com/git/git/tree/master/xdiff)
   - [lua-cjson](https://github.com/openresty/lua-cjson)
   - [Klib](https://github.com/attractivechaos/klib)
+  - [inspect.lua](https://github.com/kikito/inspect.lua)
 
 We also maintain some forks, particularly for Windows, if we are waiting on upstream changes:
 https://github.com/neovim/neovim/wiki/Deps
diff --git a/runtime/lua/vim/inspect.lua b/runtime/lua/vim/inspect.lua
index 0448ea487f..b19c215dbb 100644
--- a/runtime/lua/vim/inspect.lua
+++ b/runtime/lua/vim/inspect.lua
@@ -1,7 +1,7 @@
-local inspect ={
-  _VERSION = 'inspect.lua 3.1.0',
-  _URL     = 'http://github.com/kikito/inspect.lua',
-  _DESCRIPTION = 'human-readable representations of tables',
+local inspect = {
+  _VERSION = "inspect.lua 3.1.0",
+  _URL = "http://github.com/kikito/inspect.lua",
+  _DESCRIPTION = "human-readable representations of tables",
   _LICENSE = [[
     MIT LICENSE
 
@@ -25,13 +25,26 @@ local inspect ={
     CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
     TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
     SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-  ]]
+  ]],
 }
 
-local tostring = tostring
+inspect.KEY = setmetatable({}, {
+  __tostring = function()
+    return "inspect.KEY"
+  end,
+})
+inspect.METATABLE = setmetatable({}, {
+  __tostring = function()
+    return "inspect.METATABLE"
+  end,
+})
 
-inspect.KEY       = setmetatable({}, {__tostring = function() return 'inspect.KEY' end})
-inspect.METATABLE = setmetatable({}, {__tostring = function() return 'inspect.METATABLE' end})
+local tostring = tostring
+local rep = string.rep
+local match = string.match
+local char = string.char
+local gsub = string.gsub
+local fmt = string.format
 
 local function rawpairs(t)
   return next, t, nil
@@ -40,299 +53,289 @@ end
 -- Apostrophizes the string if it has quotes, but not aphostrophes
 -- Otherwise, it returns a regular quoted string
 local function smartQuote(str)
-  if str:match('"') and not str:match("'") then
+  if match(str, '"') and not match(str, "'") then
     return "'" .. str .. "'"
   end
-  return '"' .. str:gsub('"', '\\"') .. '"'
+  return '"' .. gsub(str, '"', '\\"') .. '"'
 end
 
 -- \a => '\\a', \0 => '\\0', 31 => '\31'
 local shortControlCharEscapes = {
-  ["\a"] = "\\a",  ["\b"] = "\\b", ["\f"] = "\\f", ["\n"] = "\\n",
-  ["\r"] = "\\r",  ["\t"] = "\\t", ["\v"] = "\\v"
+  ["\a"] = "\\a",
+  ["\b"] = "\\b",
+  ["\f"] = "\\f",
+  ["\n"] = "\\n",
+  ["\r"] = "\\r",
+  ["\t"] = "\\t",
+  ["\v"] = "\\v",
+  ["\127"] = "\\127",
 }
-local longControlCharEscapes = {} -- \a => nil, \0 => \000, 31 => \031
-for i=0, 31 do
-  local ch = string.char(i)
+local longControlCharEscapes = { ["\127"] = "\127" }
+for i = 0, 31 do
+  local ch = char(i)
   if not shortControlCharEscapes[ch] then
-    shortControlCharEscapes[ch] = "\\"..i
-    longControlCharEscapes[ch]  = string.format("\\%03d", i)
+    shortControlCharEscapes[ch] = "\\" .. i
+    longControlCharEscapes[ch] = fmt("\\%03d", i)
   end
 end
 
 local function escape(str)
-  return (str:gsub("\\", "\\\\")
-             :gsub("(%c)%f[0-9]", longControlCharEscapes)
-             :gsub("%c", shortControlCharEscapes))
+  return (gsub(gsub(gsub(str, "\\", "\\\\"), "(%c)%f[0-9]", longControlCharEscapes), "%c", shortControlCharEscapes))
 end
 
 local function isIdentifier(str)
-  return type(str) == 'string' and str:match( "^[_%a][_%a%d]*$" )
+  return type(str) == "string" and not not str:match("^[_%a][_%a%d]*$")
 end
 
+local flr = math.floor
 local function isSequenceKey(k, sequenceLength)
-  return type(k) == 'number'
-     and 1 <= k
-     and k <= sequenceLength
-     and math.floor(k) == k
+  return type(k) == "number" and flr(k) == k and 1 <= k and k <= sequenceLength
 end
 
 local defaultTypeOrders = {
-  ['number']   = 1, ['boolean']  = 2, ['string'] = 3, ['table'] = 4,
-  ['function'] = 5, ['userdata'] = 6, ['thread'] = 7
+  ["number"] = 1,
+  ["boolean"] = 2,
+  ["string"] = 3,
+  ["table"] = 4,
+  ["function"] = 5,
+  ["userdata"] = 6,
+  ["thread"] = 7,
 }
 
 local function sortKeys(a, b)
   local ta, tb = type(a), type(b)
 
   -- strings and numbers are sorted numerically/alphabetically
-  if ta == tb and (ta == 'string' or ta == 'number') then return a < b end
-
-  local dta, dtb = defaultTypeOrders[ta], defaultTypeOrders[tb]
-  -- Two default types are compared according to the defaultTypeOrders table
-  if dta and dtb then return defaultTypeOrders[ta] < defaultTypeOrders[tb]
-  elseif dta     then return true  -- default types before custom ones
-  elseif dtb     then return false -- custom types after default ones
+  if ta == tb and (ta == "string" or ta == "number") then
+    return a < b
   end
 
+  local dta = defaultTypeOrders[ta] or 100
+  local dtb = defaultTypeOrders[tb] or 100
+  -- Two default types are compared according to the defaultTypeOrders table
+
   -- custom types are sorted out alphabetically
-  return ta < tb
+  return dta == dtb and ta < tb or dta < dtb
 end
 
--- For implementation reasons, the behavior of rawlen & # is "undefined" when
--- tables aren't pure sequences. So we implement our own # operator.
-local function getSequenceLength(t)
-  local len = 1
-  local v = rawget(t,len)
-  while v ~= nil do
-    len = len + 1
-    v = rawget(t,len)
+local function getKeys(t)
+  local seqLen = 1
+  while rawget(t, seqLen) ~= nil do
+    seqLen = seqLen + 1
   end
-  return len - 1
-end
+  seqLen = seqLen - 1
 
-local function getNonSequentialKeys(t)
-  local keys, keysLength = {}, 0
-  local sequenceLength = getSequenceLength(t)
-  for k,_ in rawpairs(t) do
-    if not isSequenceKey(k, sequenceLength) then
-      keysLength = keysLength + 1
-      keys[keysLength] = k
+  local keys, keysLen = {}, 0
+  for k in rawpairs(t) do
+    if not isSequenceKey(k, seqLen) then
+      keysLen = keysLen + 1
+      keys[keysLen] = k
     end
   end
   table.sort(keys, sortKeys)
-  return keys, keysLength, sequenceLength
+  return keys, keysLen, seqLen
 end
 
-local function countTableAppearances(t, tableAppearances)
-  tableAppearances = tableAppearances or {}
-
-  if type(t) == 'table' then
-    if not tableAppearances[t] then
-      tableAppearances[t] = 1
-      for k,v in rawpairs(t) do
-        countTableAppearances(k, tableAppearances)
-        countTableAppearances(v, tableAppearances)
-      end
-      countTableAppearances(getmetatable(t), tableAppearances)
+local function countCycles(x, cycles)
+  if type(x) == "table" then
+    if cycles[x] then
+      cycles[x] = cycles[x] + 1
     else
-      tableAppearances[t] = tableAppearances[t] + 1
+      cycles[x] = 1
+      for k, v in rawpairs(x) do
+        countCycles(k, cycles)
+        countCycles(v, cycles)
+      end
+      countCycles(getmetatable(x), cycles)
     end
   end
-
-  return tableAppearances
 end
 
-local copySequence = function(s)
-  local copy, len = {}, #s
-  for i=1, len do copy[i] = s[i] end
-  return copy, len
-end
-
-local function makePath(path, ...)
-  local keys = {...}
-  local newPath, len = copySequence(path)
-  for i=1, #keys do
-    newPath[len + i] = keys[i]
+local function makePath(path, a, b)
+  local newPath = {}
+  local len = #path
+  for i = 1, len do
+    newPath[i] = path[i]
   end
+
+  newPath[len + 1] = a
+  newPath[len + 2] = b
+
   return newPath
 end
 
 local function processRecursive(process, item, path, visited)
-  if item == nil then return nil end
-  if visited[item] then return visited[item] end
+  if item == nil then
+    return nil
+  end
+  if visited[item] then
+    return visited[item]
+  end
 
   local processed = process(item, path)
-  if type(processed) == 'table' then
+  if type(processed) == "table" then
     local processedCopy = {}
     visited[item] = processedCopy
     local processedKey
 
-    for k,v in rawpairs(processed) do
+    for k, v in rawpairs(processed) do
       processedKey = processRecursive(process, k, makePath(path, k, inspect.KEY), visited)
       if processedKey ~= nil then
         processedCopy[processedKey] = processRecursive(process, v, makePath(path, processedKey), visited)
       end
     end
 
-    local mt  = processRecursive(process, getmetatable(processed), makePath(path, inspect.METATABLE), visited)
-    if type(mt) ~= 'table' then mt = nil end -- ignore not nil/table __metatable field
+    local mt = processRecursive(process, getmetatable(processed), makePath(path, inspect.METATABLE), visited)
+    if type(mt) ~= "table" then
+      mt = nil
+    end
     setmetatable(processedCopy, mt)
     processed = processedCopy
   end
   return processed
 end
 
-
-
--------------------------------------------------------------------
+local function puts(buf, str)
+  buf.n = buf.n + 1
+  buf[buf.n] = str
+end
 
 local Inspector = {}
-local Inspector_mt = {__index = Inspector}
 
-function Inspector:puts(...)
-  local args   = {...}
-  local buffer = self.buffer
-  local len    = #buffer
-  for i=1, #args do
-    len = len + 1
-    buffer[len] = args[i]
-  end
-end
+local Inspector_mt = { __index = Inspector }
 
-function Inspector:down(f)
-  self.level = self.level + 1
-  f()
-  self.level = self.level - 1
-end
-
-function Inspector:tabify()
-  self:puts(self.newline, string.rep(self.indent, self.level))
-end
-
-function Inspector:alreadyVisited(v)
-  return self.ids[v] ~= nil
+local function tabify(inspector)
+  puts(inspector.buf, inspector.newline .. rep(inspector.indent, inspector.level))
 end
 
 function Inspector:getId(v)
   local id = self.ids[v]
+  local ids = self.ids
   if not id then
     local tv = type(v)
-    id              = (self.maxIds[tv] or 0) + 1
-    self.maxIds[tv] = id
-    self.ids[v]     = id
+    id = (ids[tv] or 0) + 1
+    ids[v], ids[tv] = id, id
   end
   return tostring(id)
 end
 
-function Inspector:putKey(k)
-  if isIdentifier(k) then return self:puts(k) end
-  self:puts("[")
-  self:putValue(k)
-  self:puts("]")
-end
+function Inspector:putValue(v)
+  local buf = self.buf
+  local tv = type(v)
+  if tv == "string" then
+    puts(buf, smartQuote(escape(v)))
+  elseif
+    tv == "number"
+    or tv == "boolean"
+    or tv == "nil"
+    or tv == "cdata"
+    or tv == "ctype"
+    or (vim and v == vim.NIL)
+  then
+    puts(buf, tostring(v))
+  elseif tv == "table" and not self.ids[v] then
+    local t = v
 
-function Inspector:putTable(t)
-  if t == inspect.KEY or t == inspect.METATABLE then
-    self:puts(tostring(t))
-  elseif self:alreadyVisited(t) then
-    self:puts('<table ', self:getId(t), '>')
-  elseif self.level >= self.depth then
-    self:puts('{...}')
-  else
-    if self.tableAppearances[t] > 1 then self:puts('<', self:getId(t), '>') end
-
-    local nonSequentialKeys, nonSequentialKeysLength, sequenceLength = getNonSequentialKeys(t)
-    local mt                = getmetatable(t)
-    if (vim and sequenceLength == 0 and nonSequentialKeysLength == 0
-        and mt == vim._empty_dict_mt) then
-      self:puts(tostring(t))
-      return
-    end
-
-    self:puts('{')
-    self:down(function()
-      local count = 0
-      for i=1, sequenceLength do
-        if count > 0 then self:puts(',') end
-        self:puts(' ')
-        self:putValue(t[i])
-        count = count + 1
+    if t == inspect.KEY or t == inspect.METATABLE then
+      puts(buf, tostring(t))
+    elseif self.level >= self.depth then
+      puts(buf, "{...}")
+    else
+      if self.cycles[t] > 1 then
+        puts(buf, fmt("<%d>", self:getId(t)))
       end
 
-      for i=1, nonSequentialKeysLength do
-        local k = nonSequentialKeys[i]
-        if count > 0 then self:puts(',') end
-        self:tabify()
-        self:putKey(k)
-        self:puts(' = ')
-        self:putValue(t[k])
-        count = count + 1
+      local keys, keysLen, seqLen = getKeys(t)
+      local mt = getmetatable(t)
+
+      if vim and seqLen == 0 and keysLen == 0 and mt == vim._empty_dict_mt then
+        puts(buf, tostring(t))
+        return
       end
 
-      if type(mt) == 'table' then
-        if count > 0 then self:puts(',') end
-        self:tabify()
-        self:puts('<metatable> = ')
+      puts(buf, "{")
+      self.level = self.level + 1
+
+      for i = 1, seqLen + keysLen do
+        if i > 1 then
+          puts(buf, ",")
+        end
+        if i <= seqLen then
+          puts(buf, " ")
+          self:putValue(t[i])
+        else
+          local k = keys[i - seqLen]
+          tabify(self)
+          if isIdentifier(k) then
+            puts(buf, k)
+          else
+            puts(buf, "[")
+            self:putValue(k)
+            puts(buf, "]")
+          end
+          puts(buf, " = ")
+          self:putValue(t[k])
+        end
+      end
+
+      if type(mt) == "table" then
+        if seqLen + keysLen > 0 then
+          puts(buf, ",")
+        end
+        tabify(self)
+        puts(buf, "<metatable> = ")
         self:putValue(mt)
       end
-    end)
 
-    if nonSequentialKeysLength > 0 or type(mt) == 'table' then -- result is multi-lined. Justify closing }
-      self:tabify()
-    elseif sequenceLength > 0 then -- array tables have one extra space before closing }
-      self:puts(' ')
+      self.level = self.level - 1
+
+      if keysLen > 0 or type(mt) == "table" then
+        tabify(self)
+      elseif seqLen > 0 then
+        puts(buf, " ")
+      end
+
+      puts(buf, "}")
     end
-
-    self:puts('}')
-  end
-end
-
-function Inspector:putValue(v)
-  local tv = type(v)
-
-  if tv == 'string' then
-    self:puts(smartQuote(escape(v)))
-  elseif tv == 'number' or tv == 'boolean' or tv == 'nil' or
-         tv == 'cdata' or tv == 'ctype' or (vim and v == vim.NIL) then
-    self:puts(tostring(v))
-  elseif tv == 'table' then
-    self:putTable(v)
   else
-    self:puts('<', tv, ' ', self:getId(v), '>')
+    puts(buf, fmt("<%s %d>", tv, self:getId(v)))
   end
 end
 
--------------------------------------------------------------------
-
 function inspect.inspect(root, options)
-  options       = options or {}
+  options = options or {}
 
-  local depth   = options.depth   or math.huge
-  local newline = options.newline or '\n'
-  local indent  = options.indent  or '  '
+  local depth = options.depth or math.huge
+  local newline = options.newline or "\n"
+  local indent = options.indent or "  "
   local process = options.process
 
   if process then
     root = processRecursive(process, root, {}, {})
   end
 
+  local cycles = {}
+  countCycles(root, cycles)
+
   local inspector = setmetatable({
-    depth            = depth,
-    level            = 0,
-    buffer           = {},
-    ids              = {},
-    maxIds           = {},
-    newline          = newline,
-    indent           = indent,
-    tableAppearances = countTableAppearances(root)
+    buf = { n = 0 },
+    ids = {},
+    cycles = cycles,
+    depth = depth,
+    level = 0,
+    newline = newline,
+    indent = indent,
   }, Inspector_mt)
 
   inspector:putValue(root)
 
-  return table.concat(inspector.buffer)
+  return table.concat(inspector.buf)
 end
 
-setmetatable(inspect, { __call = function(_, ...) return inspect.inspect(...) end })
+setmetatable(inspect, {
+  __call = function(_, root, options)
+    return inspect.inspect(root, options)
+  end,
+})
 
 return inspect