lua-compat-5.3

Lua-5.3-style APIs for Lua 5.2 and 5.1.

What is it

This is a small module that aims to make it easier to write code in a Lua-5.3-style that is compatible with Lua 5.1, Lua 5.2, and Lua 5.3. This does not make Lua 5.2 (or even Lua 5.1) entirely compatible with Lua 5.3, but it brings the API closer to that of Lua 5.3.

It includes:

For writing Lua: The Lua module compat53, which can be require'd from Lua scripts and run in Lua 5.1, 5.2, and 5.3, including a backport of the utf8 module, the 5.3 table module, and the string packing functions straight from the Lua 5.3 sources.
For writing C: A C header and file which can be linked to your Lua module written in C, providing some functions from the C API of Lua 5.3 that do not exist in Lua 5.2 or 5.1, making it easier to write C code that compiles with all three versions of liblua.

How to use it

Lua module

require("compat53")

compat53 makes changes to your global environment and does not return a meaningful return value, so the usual idiom of storing the return of require in a local variable makes no sense.

When run under Lua 5.3, this module does nothing.

When run under Lua 5.2 or 5.1, it replaces some of your standard functions and adds new ones to bring your environment closer to that of Lua 5.3. It also tries to load the backported utf8, table, and string packing modules automatically. If unsuccessful, pure Lua versions of the new table functions are used as a fallback, and Roberto's struct library is tried for string packing.

C code

There are two ways of adding the C API compatibility functions/macros to your project:

If COMPAT53_PREFIX is not #defined, compat-5.3.h #includes compat-5.3.c, and all functions are made static. You don't have to compile/link/add compat-5.3.c yourself. This is useful for one-file projects.
If COMPAT53_PREFIX is #defined, all exported functions are renamed behind the scenes using this prefix to avoid linker conflicts with other code using this package. This doesn't change the way you call the compatibility functions in your code. You have to compile and link compat-5.3.c to your project yourself. You can change the way the functions are exported using the COMPAT53_API macro (e.g. if you need some __declspec magic).

What's implemented

Lua

the utf8 module backported from the Lua 5.3 sources
string.pack, string.packsize, and string.unpack from the Lua 5.3 sources or from the struct module. (struct is not 100% compatible to Lua 5.3's string packing!)
math.maxinteger and math.mininteger, math.tointeger, math.type, and math.ult
ipairs respects __index metamethod
table.move
table library respects metamethods

For Lua 5.1 additionally:

load and loadfile accept mode and env parameters
table.pack and table.unpack
string patterns may contain embedded zeros
string.rep accepts sep argument
string.format calls tostring on arguments for %s
math.log accepts base argument
xpcall takes additional arguments
pcall and xpcall can execute functions that yield
pairs respects __pairs metamethod
rawlen (but # still doesn't respect __len for tables)
package.searchers as alias for package.loaders
package.searchpath
coroutine functions dealing with the main coroutine
coroutine.create accepts functions written in C
return code of os.execute
io.write and file:write return file handle
io.lines and file:lines accept format arguments (like io.read)
debug.setmetatable returns object
debug.getuservalue and debug.setuservalue

C

lua_KContext
lua_KFunction
lua_dump (extra strip parameter, ignored)
lua_getfield (return value)
lua_geti and lua_seti
lua_getglobal (return value)
lua_getmetafield (return value)
lua_gettable (return value)
lua_getuservalue and lua_setuservalue (limited compatibility)
lua_isinteger
lua_numbertointeger
lua_callk and lua_pcallk (limited compatibility)
lua_rawget and lua_rawgeti (return values)
lua_rawgetp and lua_rawsetp
luaL_requiref (now checks package.loaded first)
lua_rotate
lua_stringtonumber

For Lua 5.1 additionally:

LUA_OK
LUA_OP* macros for lua_arith and lua_compare
lua_Unsigned
luaL_Stream
LUA_FILEHANDLE
lua_absindex
lua_arith
lua_compare
lua_len, lua_rawlen, and luaL_len
lua_copy
lua_pushglobaltable
luaL_testudata
luaL_setfuncs, luaL_newlibtable, and luaL_newlib
luaL_setmetatable
luaL_getsubtable
luaL_traceback
luaL_fileresult
luaL_checkversion (with empty body, only to avoid compile errors)
luaL_tolstring
luaL_buffinitsize, luaL_prepbuffsize, and luaL_pushresultsize
lua_pushunsigned, lua_tounsignedx, lua_tounsigned, luaL_checkunsigned, luaL_optunsigned, if LUA_COMPAT_APIINTCASTS is defined.

What's not implemented

bit operators
integer division operator
utf8 escape sequences
64 bit integers
coroutine.isyieldable
Lua 5.1: _ENV, goto, labels, ephemeron tables, etc. See lua-compat-5.2 for a detailed list.
the following C API functions/macros:
- lua_isyieldable
- lua_getextraspace
- lua_arith (new operators missing)
- lua_push(v)fstring (new formats missing)
- lua_upvalueid (5.1)
- lua_upvaluejoin (5.1)
- lua_version (5.1)
- lua_yieldk (5.1)
- luaL_execresult (5.1)
- luaL_loadbufferx (5.1)
- luaL_loadfilex (5.1)

Yieldable C functions

The emulation of lua_(p)callk for previous Lua versions is not 100% perfect, because the continuation functions in Lua 5.2 have different signatures than the ones in Lua 5.3 (and Lua 5.1 doesn't have continuation functions at all). But with the help of a small macro the same code can be used for all three Lua versions (the 5.1 version won't support yielding though).

Original Lua 5.3 code (example adapted from the Lua 5.3 manual):

static int k (lua_State *L, int status, lua_KContext ctx) {
  ...  /* code 2 */
}

int original_function (lua_State *L) {
  ...     /* code 1 */
  return k(L, lua_pcallk(L, n, m, h, ctx2, k), ctx1);
}

Portable version:

LUA_KFUNCTION( k ) {
  ...  /* code 2; parameters L, status, and ctx available here */
}

int original_function (lua_State *L) {
  ...     /* code 1 */
  return k(L, lua_pcallk(L, n, m, h, ctx2, k), ctx1);
}

Credits

This package contains code written by:

The Lua Team
Philipp Janda (@siffiejoe)
Tomás Guisasola Gorham (@tomasguisasola)
Hisham Muhammad (@hishamhm)
Renato Maia (@renatomaia)