refactor(runtime): convert dist#ft functions to lua (#18247)

Co-authored-by: Christian Clason <christian.clason@uni-due.de>

2 files changed, 455 insertions, 42 deletions

diff --git a/runtime/lua/vim/filetype.lua b/runtime/lua/vim/filetype.lua
index 911950171f..77ebb64b1d 100644
--- a/runtime/lua/vim/filetype.lua
+++ b/runtime/lua/vim/filetype.lua
@@ -784,19 +784,19 @@ local extension = {
   zsh = "zsh",
   vala = "vala",
   E = function() vim.fn["dist#ft#FTe"]() end,
-  EU = function() vim.fn["dist#ft#EuphoriaCheck"]() end,
-  EW = function() vim.fn["dist#ft#EuphoriaCheck"]() end,
-  EX = function() vim.fn["dist#ft#EuphoriaCheck"]() end,
-  EXU = function() vim.fn["dist#ft#EuphoriaCheck"]() end,
-  EXW = function() vim.fn["dist#ft#EuphoriaCheck"]() end,
+  EU = function(path, bufnr) return require("vim.filetype.detect").euphoria(bufnr) end,
+  EW = function(path, bufnr) return require("vim.filetype.detect").euphoria(bufnr) end,
+  EX = function(path, bufnr) return require("vim.filetype.detect").euphoria(bufnr) end,
+  EXU = function(path, bufnr) return require("vim.filetype.detect").euphoria(bufnr) end,
+  EXW = function(path, bufnr) return require("vim.filetype.detect").euphoria(bufnr) end,
   PL = function() vim.fn["dist#ft#FTpl"]() end,
-  R = function() vim.fn["dist#ft#FTr"]() end,
+  R = function(path, bufnr) require("vim.filetype.detect").r(bufnr) end,
   asm = function() vim.fn["dist#ft#FTasm"]() end,
   bas = function() vim.fn["dist#ft#FTbas"]() end,
   bi = function() vim.fn["dist#ft#FTbas"]() end,
   bm = function() vim.fn["dist#ft#FTbas"]() end,
   bash = function() vim.fn["dist#ft#SetFileTypeSH"]("bash") end,
-  btm = function() vim.fn["dist#ft#FTbtm"]() end,
+  btm = function(path, bufnr) return require("vim.filetype.detect").btm(bufnr) end,
   c = function() vim.fn["dist#ft#FTlpc"]() end,
   ch = function() vim.fn["dist#ft#FTchange"]() end,
   com = function() vim.fn["dist#ft#BindzoneCheck"]('dcl') end,
@@ -808,29 +808,29 @@ local extension = {
   e = function() vim.fn["dist#ft#FTe"]() end,
   ebuild = function() vim.fn["dist#ft#SetFileTypeSH"]("bash") end,
   eclass = function() vim.fn["dist#ft#SetFileTypeSH"]("bash") end,
-  ent = function() vim.fn["dist#ft#FTent"]() end,
+  ent = function(path, bufnr) return require("vim.filetype.detect").ent(bufnr) end,
   env = function() vim.fn["dist#ft#SetFileTypeSH"](vim.fn.getline(1)) end,
-  eu = function() vim.fn["dist#ft#EuphoriaCheck"]() end,
-  ew = function() vim.fn["dist#ft#EuphoriaCheck"]() end,
-  ex = function() vim.fn["dist#ft#ExCheck"]() end,
-  exu = function() vim.fn["dist#ft#EuphoriaCheck"]() end,
-  exw = function() vim.fn["dist#ft#EuphoriaCheck"]() end,
-  frm = function() vim.fn["dist#ft#FTfrm"]() end,
+  eu = function(path, bufnr) return require("vim.filetype.detect").euphoria(bufnr) end,
+  ew = function(path, bufnr) return require("vim.filetype.detect").euphoria(bufnr) end,
+  ex = function(path, bufnr) return require("vim.filetype.detect").ex(bufnr) end,
+  exu = function(path, bufnr) return require("vim.filetype.detect").euphoria(bufnr) end,
+  exw = function(path, bufnr) return require("vim.filetype.detect").euphoria(bufnr) end,
+  frm = function(path, bufnr) require("vim.filetype.detect").frm(bufnr) end,
   fs = function() vim.fn["dist#ft#FTfs"]() end,
-  h = function() vim.fn["dist#ft#FTheader"]() end,
+  h = function(path, bufnr) require("vim.filetype.detect").header(bufnr) end,
   htm = function() vim.fn["dist#ft#FThtml"]() end,
   html = function() vim.fn["dist#ft#FThtml"]() end,
   i = function() vim.fn["dist#ft#FTprogress_asm"]() end,
-  idl = function() vim.fn["dist#ft#FTidl"]() end,
+  idl = function(path, bufnr) require("vim.filetype.detect").idl(bufnr) end,
   inc = function() vim.fn["dist#ft#FTinc"]() end,
-  inp = function() vim.fn["dist#ft#Check_inp"]() end,
+  inp = function(path, bufnr) require("vim.filetype.detect").inp(bufnr) end,
   ksh = function() vim.fn["dist#ft#SetFileTypeSH"]("ksh") end,
   lst = function() vim.fn["dist#ft#FTasm"]() end,
   m = function() vim.fn["dist#ft#FTm"]() end,
   mac = function() vim.fn["dist#ft#FTasm"]() end,
-  mc = function() vim.fn["dist#ft#McSetf"]() end,
+  mc = function(path, bufnr) require("vim.filetype.detect").mc(bufnr) end,
   mm = function() vim.fn["dist#ft#FTmm"]() end,
-  mms = function() vim.fn["dist#ft#FTmms"]() end,
+  mms = function(path, bufnr) require("vim.filetype.detect").mms(bufnr) end,
   p = function() vim.fn["dist#ft#FTprogress_pascal"]() end,
   patch = function(path, bufnr)
     local firstline = getline(bufnr, 1)
@@ -844,22 +844,22 @@ local extension = {
   pp = function() vim.fn["dist#ft#FTpp"]() end,
   pro = function() vim.fn["dist#ft#ProtoCheck"]('idlang') end,
   pt = function() vim.fn["dist#ft#FThtml"]() end,
-  r = function() vim.fn["dist#ft#FTr"]() end,
-  rdf = function() vim.fn["dist#ft#Redif"]() end,
+  r = function(path, bufnr) require("vim.filetype.detect").r(bufnr) end,
+  rdf = function(path, bufnr) require("vim.filetype.detect").redif(bufnr) end,
   rules = function() vim.fn["dist#ft#FTRules"]() end,
-  sc = function() vim.fn["dist#ft#FTsc"]() end,
-  scd = function() vim.fn["dist#ft#FTscd"]() end,
+  sc = function(path, bufnr) require("vim.filetype.detect").sc(bufnr) end,
+  scd = function(path, bufnr) require("vim.filetype.detect").scd(bufnr) end,
   sh = function() vim.fn["dist#ft#SetFileTypeSH"](vim.fn.getline(1)) end,
   shtml = function() vim.fn["dist#ft#FThtml"]() end,
-  sql = function() vim.fn["dist#ft#SQL"]() end,
+  sql = function(path, bufnr) require("vim.filetype.detect").sql(bufnr) end,
   stm = function() vim.fn["dist#ft#FThtml"]() end,
   tcsh = function() vim.fn["dist#ft#SetFileTypeShell"]("tcsh") end,
   tex = function() vim.fn["dist#ft#FTtex"]() end,
-  tf = function() vim.fn["dist#ft#FTtf"]() end,
-  w = function() vim.fn["dist#ft#FTprogress_cweb"]() end,
-  xml = function() vim.fn["dist#ft#FTxml"]() end,
-  y = function() vim.fn["dist#ft#FTy"]() end,
-  zsql = function() vim.fn["dist#ft#SQL"]() end,
+  tf = function(path, bufnr) require("vim.filetype.detect").tf(bufnr) end,
+  w = function(path, bufnr) require("vim.filetype.detect").progress_cweb(bufnr) end,
+  xml = function(path, bufnr) require("vim.filetype.detect").xml(bufnr) end,
+  y = function(path, bufnr) require("vim.filetype.detect").y(bufnr) end,
+  zsql = function(path, bufnr) require("vim.filetype.detect").sql(bufnr) end,
   txt = function(path, bufnr)
     --helpfiles match *.txt, but should have a modeline as last line
     if not getline(bufnr, -1):match("vim:.*ft=help") then
@@ -933,10 +933,10 @@ local filename = {
   ["exim.conf"] = "exim",
   exports = "exports",
   [".fetchmailrc"] = "fetchmail",
-  fvSchemes = function() vim.fn["dist#ft#FTfoam"]() end,
-  fvSolution = function() vim.fn["dist#ft#FTfoam"]() end,
-  fvConstraints = function() vim.fn["dist#ft#FTfoam"]() end,
-  fvModels = function() vim.fn["dist#ft#FTfoam"]() end,
+  fvSchemes = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  fvSolution = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  fvConstraints = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  fvModels = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
   fstab = "fstab",
   mtab = "fstab",
   [".gdbinit"] = "gdb",
@@ -1355,7 +1355,7 @@ local pattern = {
   ["%.zcompdump.*"] = starsetf('zsh'),
   ["%.zlog.*"] = starsetf('zsh'),
   ["%.zsh.*"] = starsetf('zsh'),
-  [".*%.[1-9]"] = function() vim.fn["dist#ft#FTnroff"]() end,
+  [".*%.[1-9]"] = function(path, bufnr) return require("vim.filetype.detect").nroff(bufnr) end,
   [".*%.[aA]"] = function() vim.fn["dist#ft#FTasm"]() end,
   [".*%.[sS]"] = function() vim.fn["dist#ft#FTasm"]() end,
   [".*%.properties_.._.._.*"] = starsetf('jproperties'),
@@ -1434,14 +1434,14 @@ local pattern = {
   ["mutt" .. string.rep("[%w_-]", 6)] = "mail",
   ["neomutt" .. string.rep("[%w_-]", 6)] = "mail",
   ["/tmp/SLRN[0-9A-Z.]+"] = "mail",
-  ["[a-zA-Z0-9].*Dict"] = function() vim.fn["dist#ft#FTfoam"]() end,
-  ["[a-zA-Z0-9].*Dict%..*"] = function() vim.fn["dist#ft#FTfoam"]() end,
-  ["[a-zA-Z].*Properties"] = function() vim.fn["dist#ft#FTfoam"]() end,
-  ["[a-zA-Z].*Properties%..*"] = function() vim.fn["dist#ft#FTfoam"]() end,
-  [".*Transport%..*"] = function() vim.fn["dist#ft#FTfoam"]() end,
-  [".*/constant/g"] = function() vim.fn["dist#ft#FTfoam"]() end,
-  [".*/0/.*"] = function() vim.fn["dist#ft#FTfoam"]() end,
-  [".*/0%.orig/.*"] = function() vim.fn["dist#ft#FTfoam"]() end,
+  ["[a-zA-Z0-9].*Dict"] = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  ["[a-zA-Z0-9].*Dict%..*"] = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  ["[a-zA-Z].*Properties"] = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  ["[a-zA-Z].*Properties%..*"] = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  [".*Transport%..*"] = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  [".*/constant/g"] = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  [".*/0/.*"] = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
+  [".*/0%.orig/.*"] = function(path, bufnr) require("vim.filetype.detect").foam(bufnr) end,
   [".*/etc/sensors%.d/[^.].*"] = starsetf('sensors'),
   [".*%.git/.*"] = function(path, bufnr)
     local firstline = getline(bufnr, 1)
diff --git a/runtime/lua/vim/filetype/detect.lua b/runtime/lua/vim/filetype/detect.lua
new file mode 100644
index 0000000000..bb41f0956f
--- /dev/null
+++ b/runtime/lua/vim/filetype/detect.lua
@@ -0,0 +1,413 @@
+local M = {}
+
+---@private
+local function getlines(bufnr, start_lnum, end_lnum, opts)
+  if not end_lnum then
+    -- Return a single line as a string
+    return vim.api.nvim_buf_get_lines(bufnr, start_lnum - 1, start_lnum, false)[1]
+  end
+
+  local lines = vim.api.nvim_buf_get_lines(bufnr, start_lnum - 1, end_lnum, false)
+  opts = opts or {}
+  return opts.concat and (table.concat(lines) or "") or lines
+end
+
+---@private
+local function findany(s, patterns)
+  for _, v in ipairs(patterns) do
+    if s:find(v) then
+      return true
+    end
+  end
+  return false
+end
+
+-- luacheck: push no unused args
+-- luacheck: push ignore 122
+
+function M.asm(path, bufnr) end
+
+function M.asm_syntax(path, bufnr) end
+
+function M.bas(path, bufnr) end
+
+function M.bindzone(path, bufnr) end
+
+function M.btm(bufnr)
+  if vim.g.dosbatch_syntax_for_btm and vim.g.dosbatch_syntax_for_btm ~= 0 then
+    vim.bo[bufnr].filetype = "dosbatch"
+  else
+    vim.bo[bufnr].filetype = "btm"
+  end
+end
+
+-- Returns true if file content looks like RAPID
+local function is_rapid(bufnr, extension)
+  if extension == "cfg" then
+    local line = getlines(bufnr, 1):lower()
+    return findany(line, { "eio:cfg", "mmc:cfg", "moc:cfg", "proc:cfg", "sio:cfg", "sys:cfg" })
+  end
+  local first = "^%s*module%s+%S+%s*"
+  -- Called from mod, prg or sys functions
+  for _, line in ipairs(getlines(bufnr, 1, -1)) do
+    if not line:find("^%s*$") then
+      return findany(line:lower(), { "^%s*%%%%%%", first .. "(", first .. "$" })
+    end
+  end
+  -- Only found blank lines
+  return false
+end
+
+function M.cfg(bufnr)
+  if vim.g.filetype_cfg then
+    vim.bo[bufnr].filetype = vim.g.filetype_cfg
+  elseif is_rapid(bufnr, "cfg") then
+    vim.bo[bufnr].filetype = "rapid"
+  else
+    vim.bo[bufnr].filetype = "cfg"
+  end
+end
+
+function M.change(path, bufnr) end
+
+function M.csh(path, bufnr) end
+
+function M.dat(path, bufnr) end
+
+function M.dep3patch(path, bufnr) end
+
+function M.dtrace(path, bufnr) end
+
+function M.e(path, bufnr) end
+
+-- This function checks for valid cl syntax in the first five lines.
+-- Look for either an opening comment, '#', or a block start, '{'.
+-- If not found, assume SGML.
+function M.ent(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 5)) do
+    if line:find("^%s*[#{]") then
+      vim.bo[bufnr].filetype = "cl"
+      return
+    elseif not line:find("^%s*$") then
+      -- Not a blank line, not a comment, and not a block start,
+      -- so doesn't look like valid cl code.
+      break
+    end
+  end
+  vim.bo[bufnr].filetype = "dtd"
+end
+
+function M.euphoria(bufnr)
+  if vim.g.filetype_euphoria then
+    vim.bo[bufnr].filetype = vim.g.filetype_euphoria
+  else
+    vim.bo[bufnr].filetype = "euphoria3"
+  end
+end
+
+function M.ex(bufnr)
+  if vim.g.filetype_euphoria then
+    vim.bo[bufnr].filetype = vim.g.filetype_euphoria
+  else
+    for _, line in ipairs(getlines(bufnr, 1, 100)) do
+      -- TODO: in the Vim regex, \> is used to match the end of the word, can this be omitted?
+      if findany(line, { "^%-%-", "^ifdef", "^include" }) then
+        vim.bo[bufnr].filetype = "euphoria3"
+        return
+      end
+    end
+    vim.bo[bufnr].filetype = "elixir"
+  end
+end
+
+-- This function checks the first 15 lines for appearance of 'FoamFile'
+-- and then 'object' in a following line.
+-- In that case, it's probably an OpenFOAM file
+function M.foam(bufnr)
+  local foam_file = false
+  for _, line in ipairs(getlines(bufnr, 1, 15)) do
+    if line:find("^FoamFile") then
+      foam_file = true
+    elseif foam_file and line:find("^%s*object") then
+      vim.bo[bufnr].filetype = "foam"
+      return
+    end
+  end
+end
+
+function M.frm(bufnr)
+  if vim.g.filetype_frm then
+    vim.bo[bufnr].filetype = vim.g.filetype_frm
+  else
+    -- Always ignore case
+    local lines = getlines(bufnr, 1, 5, { concat = true }):lower()
+    if findany(lines, { "vb_name", "begin vb%.form", "begin vb%.mdiform" }) then
+      vim.bo[bufnr].filetype = "vb"
+    else
+      vim.bo[bufnr].filetype = "form"
+    end
+  end
+end
+
+function M.fs(path, bufnr) end
+
+function M.header(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 200)) do
+    if findany(line, { "^@interface", "^@end", "^@class" }) then
+      if vim.g.c_syntax_for_h then
+        vim.bo[bufnr].filetype = "objc"
+      else
+        vim.bo[bufnr].filetype = "objcpp"
+      end
+      return
+    end
+  end
+  if vim.g.c_syntax_for_h then
+    vim.bo[bufnr].filetype = "c"
+  elseif vim.g.ch_syntax_for_h then
+    vim.bo[bufnr].filetype = "ch"
+  else
+    vim.bo[bufnr].filetype = "cpp"
+  end
+end
+
+function M.idl(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 50)) do
+    -- Always ignore case
+    line = line:lower()
+    if findany(line, { '^%s*import%s+"unknwn"%.idl', '^%s*import%s+"objidl"%.idl' }) then
+      vim.bo[bufnr].filetype = "msidl"
+      return
+    end
+  end
+  vim.bo[bufnr].filetype = "idl"
+end
+
+function M.inc(path, bufnr) end
+
+function M.inp(bufnr)
+  if getlines(bufnr, 1):find("^%*") then
+    vim.bo[bufnr].filetype = "abaqus"
+  else
+    for _, line in ipairs(getlines(bufnr, 1, 500)) do
+      if line:lower():find("^header surface data") then
+        vim.bo[bufnr].filetype = "trasys"
+        return
+      end
+    end
+  end
+end
+
+function M.lpc(path, bufnr) end
+
+function M.lprolog(path, bufnr) end
+
+function M.m(path, bufnr) end
+
+-- Rely on the file to start with a comment.
+-- MS message text files use ';', Sendmail files use '#' or 'dnl'
+function M.mc(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 20)) do
+    if findany(line:lower(), { "^%s*#", "^%s*dnl" }) then
+      -- Sendmail .mc file
+      vim.bo[bufnr].filetype = "m4"
+      return
+    elseif line:find("^%s*;") then
+      vim.bo[bufnr].filetype = "msmessages"
+      return
+    end
+  end
+  -- Default: Sendmail .mc file
+  vim.bo[bufnr].filetype = "m4"
+end
+
+function M.mm(path, bufnr) end
+
+function M.mms(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 20)) do
+    if findany(line, { "^%s*%%", "^%s*//", "^%*" }) then
+      vim.bo[bufnr].filetype = "mmix"
+      return
+    elseif line:find("^%s*#") then
+      vim.bo[bufnr].filetype = "make"
+      return
+    end
+  end
+  vim.bo[bufnr].filetype = "mmix"
+end
+
+function M.mod(path, bufnr) end
+
+-- This function checks if one of the first five lines start with a dot. In
+-- that case it is probably an nroff file: 'filetype' is set and 1 is returned.
+function M.nroff(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 5)) do
+    if line:find("^%.") then
+      vim.bo[bufnr].filetype = "nroff"
+      return 1
+    end
+  end
+  return 0
+end
+
+function M.perl(path, bufnr) end
+
+function M.pl(path, bufnr) end
+
+function M.pp(path, bufnr) end
+
+function M.prg(path, bufnr) end
+
+function M.progress_asm(path, bufnr) end
+
+function M.progress_cweb(bufnr)
+  if vim.g.filetype_w then
+    vim.bo[bufnr].filetype = vim.g.filetype_w
+  else
+    if getlines(bufnr, 1):find("^&ANALYZE") or getlines(bufnr, 3):find("^&GLOBAL%-DEFINE") then
+      vim.bo[bufnr].filetype = "progress"
+    else
+      vim.bo[bufnr].filetype = "cweb"
+    end
+  end
+end
+
+function M.progress_pascal(path, bufnr) end
+
+function M.proto(path, bufnr) end
+
+function M.r(bufnr)
+  local lines = getlines(bufnr, 1, 50)
+  -- TODO: \< / \> which match the beginning / end of a word
+  -- Rebol is easy to recognize, check for that first
+  if table.concat(lines):lower():find("rebol") then
+    vim.bo[bufnr].filetype = "rebol"
+    return
+  end
+
+  for _, line in ipairs(lines) do
+    -- R has # comments
+    if line:find("^%s*#") then
+      vim.bo[bufnr].filetype = "r"
+      return
+    end
+    -- Rexx has /* comments */
+    if line:find("^%s*/%*") then
+      vim.bo[bufnr].filetype = "rexx"
+      return
+    end
+  end
+
+  -- Nothing recognized, use user default or assume R
+  if vim.g.filetype_r then
+    vim.bo[bufnr].filetype = vim.g.filetype_r
+  else
+    -- Rexx used to be the default, but R appears to be much more popular.
+    vim.bo[bufnr].filetype = "r"
+  end
+end
+
+function M.redif(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 5)) do
+    if line:lower():find("^template%-type:") then
+      vim.bo[bufnr].filetype = "redif"
+    end
+  end
+end
+
+function M.rules(path, bufnr) end
+
+-- This function checks the first 25 lines of file extension "sc" to resolve
+-- detection between scala and SuperCollider
+function M.sc(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 25)) do
+    if findany(line, { "[A-Za-z0-9]*%s:%s[A-Za-z0-9]", "var%s<", "classvar%s<", "%^this.*", "|%w*|", "%+%s%w*%s{", "%*ar%s" }) then
+      vim.bo[bufnr].filetype = "supercollider"
+      return
+    end
+  end
+  vim.bo[bufnr].filetype = "scala"
+end
+
+-- This function checks the first line of file extension "scd" to resolve
+-- detection between scdoc and SuperCollider
+function M.scd(bufnr)
+  local first = "^%S+%(%d[0-9A-Za-z]*%)"
+  local opt = [[%s+"[^"]*"]]
+  local line = getlines(bufnr, 1)
+  if findany(line, { "$", first .. opt .. "$", first .. opt .. opt .. "$" }) then
+    vim.bo[bufnr].filetype = "scdoc"
+  else
+    vim.bo[bufnr].filetype = "supercollider"
+  end
+end
+
+function M.sh(path, bufnr) end
+
+function M.shell(path, bufnr) end
+
+function M.sql(bufnr)
+  if vim.g.filetype_sql then
+    vim.bo[bufnr].filetype = vim.g.filetype_sql
+  else
+    vim.bo[bufnr].filetype = "sql"
+  end
+end
+
+function M.src(path, bufnr) end
+
+function M.sys(path, bufnr) end
+
+function M.tex(path, bufnr) end
+
+-- Determine if a *.tf file is TF mud client or terraform
+function M.tf(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, -1)) do
+    -- Assume terraform file on a non-empty line (not whitespace-only)
+    -- and when the first non-whitespace character is not a ; or /
+    if not line:find("^%s*$") and not line:find("^%s*[;/]") then
+      vim.bo[bufnr].filetype = "terraform"
+      return
+    end
+  end
+  vim.bo[bufnr].filetype = "tf"
+end
+
+function M.xml(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 100)) do
+    line = line:lower()
+    local is_docbook4 = line:find("<!doctype.*docbook")
+    local is_docbook5 = line:find([[ xmlns="http://docbook.org/ns/docbook"]])
+    if is_docbook4 or is_docbook5 then
+      vim.b[bufnr].docbk_type = "xml"
+      vim.b[bufnr].docbk_ver = is_docbook4 and 4 or 5
+      vim.bo[bufnr].filetype = "docbk"
+      return
+    end
+    if line:find([[xmlns:xbl="http://www.mozilla.org/xbl"]]) then
+      vim.bo[bufnr].filetype = "xbl"
+      return
+    end
+  end
+  vim.bo[bufnr].filetype = "xml"
+end
+
+function M.y(bufnr)
+  for _, line in ipairs(getlines(bufnr, 1, 100)) do
+    if line:find("^%s*%%") then
+      vim.bo[bufnr].filetype = "yacc"
+      return
+    end
+    -- TODO: in the Vim regex, \> is used to match the end of the word after "class",
+    -- can this be omitted?
+    if findany(line, { "^%s*#", "^%class", "^%s*#%s*include" }) then
+      vim.bo[bufnr].filetype = "racc"
+    end
+  end
+  vim.bo[bufnr].filetype = "yacc"
+end
+
+-- luacheck: pop
+-- luacheck: pop
+
+return M