Added test suite and API type checking for more helpful error messages.

9 files changed, 228 insertions, 124 deletions

diff --git a/core/args.lua b/core/args.lua
index 0dbf0efb..dc2af94d 100644
--- a/core/args.lua
+++ b/core/args.lua
@@ -30,8 +30,12 @@ local switches = {}
 --   help.
 -- @name register
 function M.register(short, long, narg, f, description)
-  local t = {f, narg, description}
-  switches[short], switches[long] = t, t
+  local switch = {
+    narg = assert_type(narg, 'number', 3), f = assert_type(f, 'function', 4),
+    description = assert_type(description, 'string', 5)
+  }
+  switches[assert_type(short, 'string', 1)] = switch
+  switches[assert_type(long, 'string', 2)] = switch
 end
 
 -- Processes command line argument table *arg*, handling switches previously
@@ -48,9 +52,8 @@ local function process(arg, no_emit_arg_none)
   while i <= #arg do
     local switch = switches[arg[i]]
     if switch then
-      local f, n = table.unpack(switch)
-      f(table.unpack(arg, i + 1, i + n))
-      i = i + n
+      switch.f(table.unpack(arg, i + 1, i + switch.narg))
+      i = i + switch.narg
     else
       io.open_file(lfs.abspath(arg[i], arg[-1]))
       no_args = false
@@ -67,14 +70,14 @@ if not CURSES then
   -- Shows all registered command line switches on the command line.
   M.register('-h', '--help', 0, function()
     print('Usage: textadept [args] [filenames]')
-    local line = "  %s [%d args]: %s"
     local list = {}
-    for switch in pairs(switches) do list[#list + 1] = switch end
+    for name in pairs(switches) do list[#list + 1] = name end
     table.sort(list,
                function(a, b) return a:match('[^-]+') < b:match('[^-]+') end)
     for i = 1, #list do
-      local switch = list[i]
-      print(line:format(switch, table.unpack(switches[switch], 2)))
+      local switch = switches[list[i]]
+      print(string.format('  %s [%d args]: %s', list[i], switch.narg,
+                          switch.description))
     end
     os.exit()
   end, 'Shows this')
@@ -103,12 +106,30 @@ for i = 1, #arg do
     break
   end
 end
-if not lfs.attributes(_USERHOME) then lfs.mkdir(_USERHOME) end
-local f = io.open(_USERHOME..'/init.lua', 'a+') -- ensure existence
-if f then f:close() end
+local mode = lfs.attributes(_USERHOME, 'mode')
+assert(not mode or mode == 'directory', '"%s" is not a directory', _USERHOME)
+if not mode then assert(lfs.mkdir(_USERHOME), 'cannot create %s', _USERHOME) end
+local user_init = _USERHOME..'/init.lua'
+mode = lfs.attributes(user_init, 'mode')
+assert(not mode or mode == 'file', '"%s" is not a file', user_init)
+if not mode then
+  assert(io.open(user_init, 'w'), 'unable to create %s', user_init):close()
+end
 
 -- Placeholders.
 M.register('-u', '--userhome', 1, function() end, 'Sets alternate _USERHOME')
 M.register('-f', '--force', 0, function() end, 'Forces unique instance')
 
+-- Run unit tests.
+-- Note: have them run after the last `events.INITIALIZED` handler so everything
+-- is completely initialized (e.g. menus, macro module, etc.).
+M.register('-t', '--test', 1, function(patterns)
+  events.connect(events.INITIALIZED, function()
+    local arg = {}
+    for patt in (patterns or ''):gmatch('[^,]+') do arg[#arg + 1] = patt end
+    local env = setmetatable({arg = arg}, {__index = _G})
+    assert(loadfile(_HOME..'/test.lua', 't', env))()
+  end)
+end, 'Runs unit tests indicated by comma-separated list of patterns (or all)')
+
 return M
diff --git a/core/assert.lua b/core/assert.lua
new file mode 100644
index 00000000..5517aaa3
--- /dev/null
+++ b/core/assert.lua
@@ -0,0 +1,57 @@
+-- Copyright 2020 Mitchell mitchell.att.foicica.com. See LICENSE.
+
+--[[ This comment is for LuaDoc.
+---
+-- Extends `_G` with formatted assertions and function argument type checks.
+module('assert')]]
+
+---
+-- Asserts that value *v* is not `false` or `nil` and returns *v*, or calls
+-- `error()` with *message* as the error message, defaulting to "assertion
+-- failed!". If *message* is a format string, the remaining arguments are passed
+-- to `string.format()` and the resulting string becomes the error message.
+-- @param v Value to assert.
+-- @param message Optional error message to show on error. The default value is
+--   "assertion failed!".
+-- @param ... If *message* is a format string, these arguments are passed to
+--   `string.format()`.
+-- @name _G.assert
+function assert(v, message, ...)
+  if v then return v end
+  if type(message) == 'string' and message:find('%%') then
+    message = string.format(message, ...)
+  end
+  error(message or 'assertion failed!', 2)
+end
+
+---
+-- Asserts that value *v* has type string *expected_type* and returns *v*, or
+-- calls `error()` with an error message that implicates function argument
+-- number *narg*.
+-- This is intended to be used with API function arguments so users receive more
+-- helpful error messages.
+-- @param v Value to assert the type of.
+-- @param expected_type String type to assert. It may be a punctuation-delimited
+--   list of type options.
+-- @param narg The positional argument number *v* is associated with. This is
+--   not required to be a number.
+-- @usage assert_type(filename, 'string/nil', 1)
+-- @usage assert_type(option.setting, 'number', 'setting') -- implicates key
+-- @name _G.assert_type
+function assert_type(v, expected_type, narg)
+  if type(v) == expected_type then return v end
+  -- Note: do not use assert for performance reasons.
+  if type(expected_type) ~= 'string' then
+    error(string.format("bad argument #2 to '%s' (string expected, got %s)",
+                        debug.getinfo(1, 'n').name, type(expected_type)), 2)
+  elseif narg == nil then
+    error(string.format("bad argument #3 to '%s' (value expected, got %s)",
+                        debug.getinfo(1, 'n').name, type(narg)), 2)
+  end
+  for type_option in expected_type:gmatch('%a+') do
+    if type(v) == type_option then return v end
+  end
+  error(string.format("bad argument #%s to '%s' (%s expected, got %s)", narg,
+                      debug.getinfo(2, 'n').name or '?', expected_type,
+                      type(v)), 3)
+end
diff --git a/core/events.lua b/core/events.lua
index 543133da..438bb5bf 100644
--- a/core/events.lua
+++ b/core/events.lua
@@ -311,7 +311,9 @@ end})
 -- @see disconnect
 -- @name connect
 function M.connect(event, f, index)
-  assert(type(event) == 'string', 'string expected')
+  assert_type(event, 'string', 1)
+  assert_type(f, 'function', 2)
+  assert_type(index, 'number/nil', 3)
   M.disconnect(event, f) -- in case it already exists
   table.insert(handlers[event], index or #handlers[event] + 1, f)
 end
@@ -323,7 +325,8 @@ end
 -- @see connect
 -- @name disconnect
 function M.disconnect(event, f)
-  for i = 1, #handlers[event] do
+  assert_type(f, 'function', 2)
+  for i = 1, #handlers[assert_type(event, 'string', 1)] do
     if handlers[event][i] == f then table.remove(handlers[event], i) break end
   end
 end
@@ -344,10 +347,10 @@ local error_emitted = false
 -- @usage events.emit('my_event', 'my message')
 -- @name emit
 function M.emit(event, ...)
-  assert(type(event) == 'string', 'string expected')
+  local event_handlers = handlers[assert_type(event, 'string', 1)]
   local i = 1
-  while i <= #handlers[event] do
-    local handler = handlers[event][i]
+  while i <= #event_handlers do
+    local handler = event_handlers[i]
     local ok, result = pcall(handler, ...)
     if not ok then
       if not error_emitted then
@@ -359,7 +362,7 @@ function M.emit(event, ...)
       end
     end
     if type(result) == 'boolean' then return result end
-    if handlers[event][i] == handler then i = i + 1 end -- unless M.disconnect()
+    if event_handlers[i] == handler then i = i + 1 end -- unless M.disconnect()
   end
 end
 
diff --git a/core/file_io.lua b/core/file_io.lua
index 97977b77..846b4a86 100644
--- a/core/file_io.lua
+++ b/core/file_io.lua
@@ -95,32 +95,31 @@ io.encodings = {'UTF-8', 'ASCII', 'CP1252', 'UTF-16'}
 -- @see _G.events
 -- @name open_file
 function io.open_file(filenames, encodings)
+  assert_type(encodings, 'string/table/nil', 2)
+  if not assert_type(filenames, 'string/table/nil', 1) then
+    filenames = ui.dialogs.fileselect{
+      title = _L['Open File'], select_multiple = true,
+      with_directory = (buffer.filename or ''):match('^.+[/\\]') or
+                       lfs.currentdir(),
+      width = CURSES and ui.size[1] - 2 or nil
+    }
+    if not filenames then return end
+  end
   if type(filenames) == 'string' then filenames = {filenames} end
-  if type(encodings or '') == 'string' then encodings = {encodings} end
-  filenames = filenames or ui.dialogs.fileselect{
-    title = _L['Open File'], select_multiple = true,
-    with_directory = (buffer.filename or ''):match('^.+[/\\]') or
-                     lfs.currentdir(),
-    width = CURSES and ui.size[1] - 2 or nil
-  }
-  if not filenames then return end
+  if type(encodings) ~= 'table' then encodings = {encodings} end
   for i = 1, #filenames do
     local filename = lfs.abspath((filenames[i]:gsub('^file://', '')))
-    for j = 1, #_BUFFERS do
-      if filename == _BUFFERS[j].filename then
-        view:goto_buffer(_BUFFERS[j]) -- already open
-        goto continue
-      end
+    for _, buf in ipairs(_BUFFERS) do
+      if filename == buf.filename then view:goto_buffer(buf) goto continue end
     end
 
     local text = ''
-    local f, err = io.open(filename, 'rb')
-    if f then
+    if lfs.attributes(filename) then
+      local f, errmsg = io.open(filename, 'rb')
+      if not f then error(string.format('cannot open %s', errmsg), 2) end
       text = f:read('a')
       f:close()
       if not text then goto continue end -- filename exists, but cannot read it
-    elseif lfs.attributes(filename) then
-      error(err)
     end
     local buffer = buffer.new()
     if encodings[i] then
@@ -128,11 +127,11 @@ function io.open_file(filenames, encodings)
     else
       -- Try to detect character encoding and convert to UTF-8.
       local has_zeroes = text:sub(1, 65536):find('\0')
-      for j = 1, #io.encodings do
-        if not has_zeroes or io.encodings[j]:find('^UTF%-[13][62]') then
-          local ok, conv = pcall(string.iconv, text, 'UTF-8', io.encodings[j])
+      for _, encoding in ipairs(io.encodings) do
+        if not has_zeroes or encoding:find('^UTF%-[13][62]') then
+          local ok, conv = pcall(string.iconv, text, 'UTF-8', encoding)
           if ok then
-            buffer.encoding, text = io.encodings[j], conv
+            buffer.encoding, text = encoding, conv
             goto encoding_detected
           end
         end
@@ -185,6 +184,7 @@ end
 
 -- LuaDoc is in core/.buffer.luadoc.
 local function set_encoding(buffer, encoding)
+  assert_type(encoding, 'string/nil', 1)
   local pos, first_visible_line = buffer.current_pos, buffer.first_visible_line
   local text = buffer:get_text()
   if buffer.encoding then
@@ -229,12 +229,14 @@ end
 -- @name save_file_as
 function io.save_file_as(filename)
   local dir, name = (buffer.filename or ''):match('^(.-[/\\]?)([^/\\]*)$')
-  filename = filename or ui.dialogs.filesave{
-    title = _L['Save File'], with_directory = dir,
-    with_file = name:iconv('UTF-8', _CHARSET),
-    width = CURSES and ui.size[1] - 2 or nil
-  }
-  if not filename then return end
+  if not assert_type(filename, 'string/nil', 1) then
+    filename = ui.dialogs.filesave{
+      title = _L['Save File'], with_directory = dir,
+      with_file = name:iconv('UTF-8', _CHARSET),
+      width = CURSES and ui.size[1] - 2 or nil
+    }
+    if not filename then return end
+  end
   buffer.filename = filename
   io.save_file()
   events.emit(events.FILE_AFTER_SAVE, filename, true)
@@ -246,9 +248,9 @@ end
 -- @name save_all_files
 function io.save_all_files()
   local current_buffer = buffer
-  for i = 1, #_BUFFERS do
-    if _BUFFERS[i].filename and _BUFFERS[i].modify then
-      view:goto_buffer(_BUFFERS[i])
+  for _, buffer in ipairs(_BUFFERS) do
+    if buffer.filename and buffer.modify then
+      view:goto_buffer(buffer)
       io.save_file()
     end
   end
@@ -358,11 +360,11 @@ local vcs = {'.bzr', '.git', '.hg', '.svn'}
 -- @return string root or nil
 -- @name get_project_root
 function io.get_project_root(path)
-  local lfs_attributes = lfs.attributes
-  local dir = path or (buffer.filename or lfs.currentdir()..'/'):match('^(.+)[/\\]')
+  local dir = assert_type(path, 'string/nil', 1) or
+              (buffer.filename or lfs.currentdir()..'/'):match('^(.+)[/\\]')
   while dir do
     for i = 1, #vcs do
-      if lfs_attributes(dir..'/'..vcs[i], 'mode') then return dir end
+      if lfs.attributes(dir..'/'..vcs[i], 'mode') then return dir end
     end
     dir = dir:match('^(.+)[/\\]')
   end
@@ -414,8 +416,12 @@ io.quick_open_filters = {}
 -- @see ui.dialogs.filteredlist
 -- @name quick_open
 function io.quick_open(paths, filter, opts)
-  if not paths then paths = io.get_project_root() end
-  if not paths then return end
+  if not assert_type(paths, 'string/table/nil', 1) then
+    paths = io.get_project_root()
+    if not paths then return end
+  end
+  assert_type(filter, 'string/table/nil', 2)
+  assert_type(opts, 'table/nil', 3)
   if type(paths) == 'string' then
     if not filter then filter = io.quick_open_filters[paths] end
     paths = {paths}
@@ -429,11 +435,12 @@ function io.quick_open(paths, filter, opts)
     end, filter or lfs.default_filter)
   end
   if #utf8_list >= io.quick_open_max then
-    local msg = string.format('%d %s %d', io.quick_open_max,
-                              _L['files or more were found. Showing the first'],
-                              io.quick_open_max)
     ui.dialogs.msgbox{
-      title = _L['File Limit Exceeded'], text = msg, icon = 'gtk-dialog-info'
+      title = _L['File Limit Exceeded'],
+      text = string.format('%d %s %d', io.quick_open_max,
+                           _L['files or more were found. Showing the first'],
+                           io.quick_open_max),
+      icon = 'gtk-dialog-info'
     }
   end
   local options = {
diff --git a/core/init.lua b/core/init.lua
index f2d727d1..0f187e0a 100644
--- a/core/init.lua
+++ b/core/init.lua
@@ -6,6 +6,11 @@ _COPYRIGHT = 'Copyright © 2007-2020 Mitchell. See LICENSE.\n'..
 
 package.path = _HOME..'/core/?.lua;'..package.path
 
+--for i = 1, #arg do
+--  if arg[i] == '-t' or arg[i] == '--test' then pcall(require, 'luacov') end
+--end
+
+require('assert')
 _SCINTILLA = require('iface')
 events = require('events')
 args = require('args')
@@ -14,22 +19,22 @@ require('file_io')
 require('lfs_ext')
 require('ui')
 keys = require('keys')
-
 _M = {} -- language modules table
+
 -- pdcurses compatibility.
 if CURSES and WIN32 then
   function os.spawn(argv, ...)
     local current_dir = lfs.currentdir()
-    local i = 1
-    if type(select(i, ...) or nil) == 'string' then
-      lfs.chdir(select(i, ...)) -- cwd
+    local args, i = {...}, 1
+    if type(args[i]) == 'string' then
+      lfs.chdir(args[i]) -- cwd
       i = i + 1
     end
-    if type(select(i, ...) or nil) == 'table' then i = i + 1 end -- env (ignore)
+    if type(args[i]) == 'table' then i = i + 1 end -- env (ignore)
     local p = io.popen(argv..' 2>&1')
-    if select(i, ...) then select(i, ...)(p:read('a')) end -- stdout_cb
+    if type(args[i]) == 'function' then args[i](p:read('a')) end -- stdout_cb
     local status = select(3, p:close())
-    if select(i + 2, ...) then select(i + 2, ...)(status) end -- exit_cb
+    if type(args[i + 2]) == 'function' then args[i + 2](status) end -- exit_cb
     lfs.chdir(current_dir)
     return p
   end
@@ -39,6 +44,8 @@ end
 -- argument.
 -- Documentation is in core/.buffer.luadoc.
 local function text_range(buffer, start_pos, end_pos)
+  assert_type(start_pos, 'number', 2)
+  assert_type(end_pos, 'number', 3)
   local target_start, target_end = buffer.target_start, buffer.target_end
   if start_pos < 0 then start_pos = 0 end
   if end_pos > buffer.length then end_pos = buffer.length end
diff --git a/core/keys.lua b/core/keys.lua
index 35af9bc8..a6a9207a 100644
--- a/core/keys.lua
+++ b/core/keys.lua
@@ -88,9 +88,9 @@ local M = {}
 -- ## Key Chains
 --
 -- Key chains are a powerful concept. They allow you to assign multiple key
--- bindings to one key sequence. By default, the `Esc` (`⎋` on Mac OSX | `Esc`
--- in curses) key cancels a key chain, but you can redefine it via
--- [`keys.CLEAR`](). An example key chain looks like:
+-- bindings to one key sequence. By default, the `Esc` key cancels a key chain,
+-- but you can redefine it via [`keys.CLEAR`](). An example key chain looks
+-- like:
 --
 --     keys['aa'] = {
 --       a = function1,
@@ -205,10 +205,13 @@ local function keypress(code, shift, control, alt, meta, caps_lock)
   local key = code < 256 and (not CURSES or (code ~= 7 and code ~= 13)) and
               string.char(code) or M.KEYSYMS[code]
   if not key then return end
-  shift = shift and (code >= 256 or code == 9) -- printable chars are uppercased
-  if OSX and alt and code < 256 then alt = false end -- composed key; ignore alt
-  local key_seq = (control and CTRL or '')..(alt and ALT or '')..
-                  (meta and OSX and META or '')..(shift and SHIFT or '')..key
+  -- Since printable characters are uppercased, disable shift.
+  if shift and code < 256 and code ~= 9 then shift = false end
+  -- For composed keys on OSX, ignore alt.
+  if OSX and alt and code < 256 then alt = false end
+  local key_seq = string.format('%s%s%s%s%s', control and CTRL or '',
+                                alt and ALT or '', meta and OSX and META or '',
+                                shift and SHIFT or '', key)
   --print(key_seq)
 
   ui.statusbar_text = ''
diff --git a/core/lfs_ext.lua b/core/lfs_ext.lua
index c71c42bc..6d9fe2af 100644
--- a/core/lfs_ext.lua
+++ b/core/lfs_ext.lua
@@ -48,6 +48,10 @@ lfs.default_filter = {
 -- @see filter
 -- @name dir_foreach
 function lfs.dir_foreach(dir, f, filter, n, include_dirs, level)
+  assert_type(dir, 'string', 1)
+  assert_type(f, 'function', 2)
+  assert_type(filter, 'string/table/nil', 3)
+  assert_type(n, 'number/nil', 4)
   if not level then
     -- Convert filter to a table from nil or string arguments.
     if not filter then filter = lfs.default_filter end
@@ -60,8 +64,7 @@ function lfs.dir_foreach(dir, f, filter, n, include_dirs, level)
       consider_any = true,
       exts = setmetatable({}, {__index = function() return true end})
     }
-    for i = 1, #filter do
-      local patt = filter[i]
+    for _, patt in ipairs(filter) do
       patt = patt:gsub('^(!?)%%?%.([^.]+)$', '%1%%.%2$') -- '.lua' to '%.lua$'
       patt = patt:gsub('/([^\\])', '[/\\]%1') -- '/' to '[/\\]'
       local include = not patt:find('^!')
@@ -76,10 +79,9 @@ function lfs.dir_foreach(dir, f, filter, n, include_dirs, level)
     end
     filter = processed_filter
   end
-  local dir_sep = not WIN32 and '/' or '\\'
   for basename in lfs.dir(dir) do
     if basename:find('^%.%.?$') then goto continue end -- ignore . and ..
-    local filename = dir..(dir ~= '/' and dir_sep or '')..basename
+    local filename = dir..(dir ~= '/' and '/' or '')..basename
     local mode = lfs.attributes(filename, 'mode')
     if mode ~= 'directory' and mode ~= 'file' then goto continue end
     local include
@@ -90,22 +92,23 @@ function lfs.dir_foreach(dir, f, filter, n, include_dirs, level)
     elseif mode == 'directory' then
       include = filter.consider_any
     end
-    for i = 1, #filter do
-      local patt = filter[i]
+    for _, patt in ipairs(filter) do
       -- Treat exclusive patterns as logical AND.
       if patt:find('^!') and filename:find(patt:sub(2)) then goto continue end
       -- Treat inclusive patterns as logical OR.
       include = include or (not patt:find('^!') and filename:find(patt))
     end
+    local dir_sep = not WIN32 and '/' or '\\'
+    local os_filename = not WIN32 and filename or filename:gsub('/', dir_sep)
     if include and mode == 'directory' then
-      if include_dirs and f(filename..dir_sep) == false then return end
+      if include_dirs and f(os_filename..dir_sep) == false then return end
       if not n or (level or 0) < n then
         local halt = lfs.dir_foreach(filename, f, filter, n, include_dirs,
                                      (level or 0) + 1) == false
         if halt then return false end
       end
     elseif include and mode == 'file' then
-      if f(filename) == false then return false end
+      if f(os_filename) == false then return false end
     end
     ::continue::
   end
@@ -120,6 +123,8 @@ end
 -- @return string absolute path
 -- @name abspath
 function lfs.abspath(filename, prefix)
+  assert_type(filename, 'string', 1)
+  assert_type(prefix, 'string/nil', 2)
   if WIN32 then filename = filename:gsub('/', '\\') end
   if not filename:find(not WIN32 and '^/' or '^%a:[/\\]') and
      not (WIN32 and filename:find('^\\\\')) then
diff --git a/core/locale.lua b/core/locale.lua
index 48de4af5..45a0f855 100644
--- a/core/locale.lua
+++ b/core/locale.lua
@@ -23,12 +23,12 @@ for line in f:lines() do
   -- comment.
   if not line:find('^%s*[^%w_%[]') then
     local id, str = line:match('^(.-)%s*=%s*(.+)$')
-    if id and str and assert(not M[id], 'duplicate locale key: '..id) then
+    if id and str and assert(not M[id], 'duplicate locale key "%s"', id) then
       M[id] = not CURSES and str or str:gsub('_', '')
     end
   end
 end
 f:close()
 
-return setmetatable(M,
-                    {__index = function(_, k) return 'No Localization:'..k end})
+setmetatable(M, {__index = function(_, k) return 'No Localization:'..k end})
+return M
diff --git a/core/ui.lua b/core/ui.lua
index b5c46114..65b1fb4d 100644
--- a/core/ui.lua
+++ b/core/ui.lua
@@ -41,11 +41,8 @@ ui.silent_print = false
 -- @see ui._print
 local function _print(buffer_type, ...)
   local print_buffer
-  for i = 1, #_BUFFERS do
-    if _BUFFERS[i]._type == buffer_type then
-      print_buffer = _BUFFERS[i]
-      break
-    end
+  for _, buffer in ipairs(_BUFFERS) do
+    if buffer._type == buffer_type then print_buffer = buffer break end
   end
   if not print_buffer then
     if not ui.tabs then view:split() end
@@ -53,13 +50,10 @@ local function _print(buffer_type, ...)
     print_buffer._type = buffer_type
     events.emit(events.FILE_OPENED)
   elseif not ui.silent_print then
-    for i = 1, #_VIEWS do
-      local view = _VIEWS[i]
+    for _, view in ipairs(_VIEWS) do
       if view.buffer._type == buffer_type then ui.goto_view(view) break end
     end
-    if view.buffer._type ~= buffer_type then
-      view:goto_buffer(print_buffer)
-    end
+    if view.buffer._type ~= buffer_type then view:goto_buffer(print_buffer) end
   end
   local args, n = {...}, select('#', ...)
   for i = 1, n do args[i] = tostring(args[i]) end
@@ -78,7 +72,9 @@ end
 -- @param ... Message strings.
 -- @usage ui._print(_L['[Message Buffer]'], message)
 -- @name _print
-function ui._print(buffer_type, ...) _print(buffer_type, ...) end
+function ui._print(buffer_type, ...)
+  _print(assert_type(buffer_type, 'string', 1), ...)
+end
 
 ---
 -- Prints the given string messages to the message buffer.
@@ -87,6 +83,16 @@ function ui._print(buffer_type, ...) _print(buffer_type, ...) end
 -- @name print
 function ui.print(...) ui._print(_L['[Message Buffer]'], ...) end
 
+-- Returns 0xBBGGRR colors transformed into "#RRGGBB" for the colorselect
+-- dialog.
+-- @param value Number color to transform.
+-- @return string or nil if the transform failed
+local function torgb(value)
+  local bbggrr = string.format('%06X', value)
+  local b, g, r = bbggrr:match('^(%x%x)(%x%x)(%x%x)$')
+  return r and g and b and string.format('#%s%s%s', r, g, b) or nil
+end
+
 -- Documentation is in core/.ui.dialogs.luadoc.
 ui.dialogs = setmetatable({}, {__index = function(_, k)
   -- Wrapper for `ui.dialog(k)`, transforming the given table of arguments into
@@ -106,22 +112,23 @@ ui.dialogs = setmetatable({}, {__index = function(_, k)
     -- Transform key-value pairs into command line arguments.
     local args = {}
     for option, value in pairs(options) do
+      assert_type(value, 'string/number/table/boolean', option)
       if value then
         args[#args + 1] = '--'..option:gsub('_', '-')
-        if option == 'color' or
-           option == 'palette' and type(value) ~= 'boolean' then
-          -- Transform 0xBBGGRR colors into "#RRGGBB" for color selector.
-          if type(value) ~= 'table' then value = {value} end
-          for i = 1, #value do
-            if type(value[i]) == 'number' then
-              local bbggrr = string.format('%06X', value[i])
-              local b, g, r = bbggrr:match('^(%x%x)(%x%x)(%x%x)$')
-              if r and g and b then value[i] = '#'..r..g..b end
+        if type(value) == 'boolean' then goto continue end
+        if type(value) == 'table' then
+          for i, val in ipairs(value) do
+            assert_type(val, 'string/number', option..'['..i..']')
+            if option == 'palette' and type(val) == 'number' then
+              value[i] = torgb(val) -- nil return is okay
             end
           end
+        elseif option == 'color' and type(value) == 'number' then
+          value = torgb(value)
         end
-        if type(value) ~= 'boolean' then args[#args + 1] = value end
+        args[#args + 1] = value
       end
+      ::continue::
     end
     -- Call gtdialog, stripping any trailing newline in the standard output.
     local result = ui.dialog(k:gsub('_', '-'), table.unpack(args))
@@ -153,7 +160,8 @@ ui.dialogs = setmetatable({}, {__index = function(_, k)
     elseif k == 'colorselect' then
       if options.string_output then return result ~= '' and result or nil end
       local r, g, b = result:match('^#(%x%x)(%x%x)(%x%x)$')
-      return r and g and b and tonumber('0x'..b..g..r) or nil
+      local bgr = r and g and b and string.format('0x%s%s%s', b, g, r) or nil
+      return tonumber(bgr)
     elseif k == 'fontselect' then
       return result ~= '' and result or nil
     elseif not options.string_output then
@@ -246,8 +254,9 @@ end
 --   is `false`.
 -- @name goto_file
 function ui.goto_file(filename, split, preferred_view, sloppy)
-  local patt = '^'..filename..'$' -- TODO: escape filename properly
-  if sloppy then patt = filename:match('[^/\\]+$')..'$' end
+  assert_type(filename, 'string', 1)
+  local patt = not sloppy and '^'..filename..'$' or
+               filename:match('[^/\\]+$')..'$' -- TODO: escape filename properly
   if WIN32 then
     patt = patt:gsub('%a', function(letter)
       return string.format('[%s%s]', letter:upper(), letter:lower())
@@ -257,20 +266,15 @@ function ui.goto_file(filename, split, preferred_view, sloppy)
     view:split()
   else
     local other_view = _VIEWS[preferred_view]
-    for i = 1, #_VIEWS do
-      if (_VIEWS[i].buffer.filename or ''):find(patt) then
-        ui.goto_view(_VIEWS[i])
-        return
-      end
-      if not other_view and _VIEWS[i] ~= view then other_view = _VIEWS[i] end
+    for _, view in ipairs(_VIEWS) do
+      local filename = view.buffer.filename or ''
+      if filename:find(patt) then ui.goto_view(view) return end
+      if not other_view and view ~= _G.view then other_view = view end
     end
     if other_view then ui.goto_view(other_view) end
   end
-  for i = 1, #_BUFFERS do
-    if (_BUFFERS[i].filename or ''):find(patt) then
-      view:goto_buffer(_BUFFERS[i])
-      return
-    end
+  for _, buf in ipairs(_BUFFERS) do
+    if (buf.filename or ''):find(patt) then view:goto_buffer(buf) return end
   end
   io.open_file(filename)
 end
@@ -418,13 +422,10 @@ events_connect(events.RESET_AFTER,
 -- Prompts for confirmation if any buffers are modified.
 events_connect(events.QUIT, function()
   local utf8_list = {}
-  for i = 1, #_BUFFERS do
-    if _BUFFERS[i].modify then
-      local filename = _BUFFERS[i].filename or _BUFFERS[i]._type or
-                       _L['Untitled']
-      if _BUFFERS[i].filename then
-        filename = filename:iconv('UTF-8', _CHARSET)
-      end
+  for _, buffer in ipairs(_BUFFERS) do
+    if buffer.modify then
+      local filename = buffer.filename or buffer._type or _L['Untitled']
+      if buffer.filename then filename = filename:iconv('UTF-8', _CHARSET) end
       utf8_list[#utf8_list + 1] = filename
     end
   end