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Lua module 'compat_env' - Lua 5.1/5.2 environment compatibility functions

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compat_env.lua
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--[[
 
compat_env v$(_VERSION) - Lua 5.1/5.2 environment compatibility functions
 
SYNOPSIS
 
-- Get load/loadfile compatibility functions only if using 5.1.
local CL = pcall(load, '') and _G or require 'compat_env'
local load = CL.load
local loadfile = CL.loadfile
-- The following now works in both Lua 5.1 and 5.2:
assert(load('return 2*pi', nil, 't', {pi=math.pi}))()
assert(loadfile('ex.lua', 't', {print=print}))()
-- Get getfenv/setfenv compatibility functions only if using 5.2.
local getfenv = _G.getfenv or require 'compat_env'.getfenv
local setfenv = _G.setfenv or require 'compat_env'.setfenv
local function f() return x end
setfenv(f, {x=2})
print(x, getfenv(f).x) --> 2, 2
 
DESCRIPTION
 
This module provides Lua 5.1/5.2 environment related compatibility functions.
This includes implementations of Lua 5.2 style `load` and `loadfile`
for use in Lua 5.1. It also includes Lua 5.1 style `getfenv` and `setfenv`
for use in Lua 5.2.
API
 
local CL = require 'compat_env'
CL.load (ld [, source [, mode [, env] ] ]) --> f [, err]
 
This behaves the same as the Lua 5.2 `load` in both
Lua 5.1 and 5.2.
http://www.lua.org/manual/5.2/manual.html#pdf-load
CL.loadfile ([filename [, mode [, env] ] ]) --> f [, err]
This behaves the same as the Lua 5.2 `loadfile` in both
Lua 5.1 and 5.2.
http://www.lua.org/manual/5.2/manual.html#pdf-loadfile
CL.getfenv ([f]) --> t
 
This is identical to the Lua 5.1 `getfenv` in Lua 5.1.
This behaves similar to the Lua 5.1 `getfenv` in Lua 5.2.
When a global environment is to be returned, or when `f` is a
C function, this returns `_G` since Lua 5.2 doesn't have
(thread) global and C function environments. This will also
return `_G` if the Lua function `f` lacks an `_ENV`
upvalue, but it will raise an error if uncertain due to lack of
debug info. It is not normally considered good design to use
this function; when possible, use `load` or `loadfile` instead.
http://www.lua.org/manual/5.1/manual.html#pdf-getfenv
CL.setfenv (f, t)
This is identical to the Lua 5.1 `setfenv` in Lua 5.1.
This behaves similar to the Lua 5.1 `setfenv` in Lua 5.2.
This will do nothing if `f` is a Lua function that
lacks an `_ENV` upvalue, but it will raise an error if uncertain
due to lack of debug info. See also Design Notes below.
It is not normally considered good design to use
this function; when possible, use `load` or `loadfile` instead.
http://www.lua.org/manual/5.1/manual.html#pdf-setfenv
DESIGN NOTES
 
This module intends to provide robust and fairly complete reimplementations
of the environment related Lua 5.1 and Lua 5.2 functions.
No effort is made, however, to simulate rare or difficult to simulate features,
such as thread environments, although this is liable to change in the future.
Such 5.1 capabilities are discouraged and ideally
removed from 5.1 code, thereby allowing your code to work in both 5.1 and 5.2.
In Lua 5.2, a `setfenv(f, {})`, where `f` lacks any upvalues, will be silently
ignored since there is no `_ENV` in this function to write to, and the
environment will have no effect inside the function anyway. However,
this does mean that `getfenv(setfenv(f, t))` does not necessarily equal `t`,
which is incompatible with 5.1 code (a possible workaround would be [1]).
If `setfenv(f, {})` has an upvalue but no debug info, then this will raise
an error to prevent inadvertently executing potentially untrusted code in the
global environment.
It is not normally considered good design to use `setfenv` and `getfenv`
(one reason they were removed in 5.2). When possible, consider replacing
these with `load` or `loadfile`, which are more restrictive and have native
implementations in 5.2.
This module might be merged into a more general Lua 5.1/5.2 compatibility
library (e.g. a full reimplementation of Lua 5.2 `_G`). However,
`load/loadfile/getfenv/setfenv` perhaps are among the more cumbersome
functions not to have.
 
INSTALLATION
 
Download compat_env.lua:
wget https://raw.github.com/gist/1654007/compat_env.lua
 
Copy compat_env.lua into your LUA_PATH.
Alternately, unpack, test, and install into LuaRocks:
wget https://raw.github.com/gist/1422205/sourceunpack.lua
lua sourceunpack.lua compat_env.lua
(cd out && luarocks make)
 
Related work
 
http://lua-users.org/wiki/LuaVersionCompatibility
https://github.com/stevedonovan/Penlight/blob/master/lua/pl/utils.lua
- penlight implementations of getfenv/setfenv
http://lua-users.org/lists/lua-l/2010-06/msg00313.html
- initial getfenv/setfenv implementation
References
 
[1] http://lua-users.org/lists/lua-l/2010-06/msg00315.html
 
Copyright
 
(c) 2012 David Manura. Licensed under the same terms as Lua 5.1/5.2 (MIT license).
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY 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 M = {_TYPE='module', _NAME='compat_env', _VERSION='0.2.20120124'}
 
local function check_chunk_type(s, mode)
local nmode = mode or 'bt'
local is_binary = s and #s > 0 and s:byte(1) == 27
if is_binary and not nmode:match'b' then
return nil, ("attempt to load a binary chunk (mode is '%s')"):format(mode)
elseif not is_binary and not nmode:match't' then
return nil, ("attempt to load a text chunk (mode is '%s')"):format(mode)
end
return true
end
 
local IS_52_LOAD = pcall(load, '')
if IS_52_LOAD then
M.load = _G.load
M.loadfile = _G.loadfile
else
-- 5.2 style `load` implemented in 5.1
function M.load(ld, source, mode, env)
local f
if type(ld) == 'string' then
local s = ld
local ok, err = check_chunk_type(s, mode); if not ok then return ok, err end
local err; f, err = loadstring(s, source); if not f then return f, err end
elseif type(ld) == 'function' then
local ld2 = ld
if (mode or 'bt') ~= 'bt' then
local first = ld()
local ok, err = check_chunk_type(first, mode); if not ok then return ok, err end
ld2 = function()
if first then
local chunk=first; first=nil; return chunk
else return ld() end
end
end
local err; f, err = load(ld2, source); if not f then return f, err end
else
error(("bad argument #1 to 'load' (function expected, got %s)"):format(type(ld)), 2)
end
if env then setfenv(f, env) end
return f
end
 
-- 5.2 style `loadfile` implemented in 5.1
function M.loadfile(filename, mode, env)
if (mode or 'bt') ~= 'bt' then
local ioerr
local fh, err = io.open(filename, 'rb'); if not fh then return fh, err end
local function ld() local chunk; chunk,ioerr = fh:read(4096); return chunk end
local f, err = M.load(ld, filename and '@'..filename, mode, env)
fh:close()
if not f then return f, err end
if ioerr then return nil, ioerr end
return f
else
local f, err = loadfile(filename); if not f then return f, err end
if env then setfenv(f, env) end
return f
end
end
end
 
if _G.setfenv then -- Lua 5.1
M.setfenv = _G.setfenv
M.getfenv = _G.getfenv
else -- >= Lua 5.2
-- helper function for `getfenv`/`setfenv`
local function envlookup(f)
local name, val
local up = 0
local unknown
repeat
up=up+1; name, val = debug.getupvalue(f, up)
if name == '' then unknown = true end
until name == '_ENV' or name == nil
if name ~= '_ENV' then
up = nil
if unknown then error("upvalues not readable in Lua 5.2 when debug info missing", 3) end
end
return (name == '_ENV') and up, val, unknown
end
 
-- helper function for `getfenv`/`setfenv`
local function envhelper(f, name)
if type(f) == 'number' then
if f < 0 then
error(("bad argument #1 to '%s' (level must be non-negative)"):format(name), 3)
elseif f < 1 then
error("thread environments unsupported in Lua 5.2", 3) --[*]
end
f = debug.getinfo(f+2, 'f').func
elseif type(f) ~= 'function' then
error(("bad argument #1 to '%s' (number expected, got %s)"):format(type(name, f)), 2)
end
return f
end
-- [*] might simulate with table keyed by coroutine.running()
-- 5.1 style `setfenv` implemented in 5.2
function M.setfenv(f, t)
local f = envhelper(f, 'setfenv')
local up, val, unknown = envlookup(f)
if up then
debug.upvaluejoin(f, up, function() return up end, 1) -- unique upvalue [*]
debug.setupvalue(f, up, t)
else
local what = debug.getinfo(f, 'S').what
if what ~= 'Lua' and what ~= 'main' then -- not Lua func
error("'setfenv' cannot change environment of given object", 2)
end -- else ignore no _ENV upvalue (warning: incompatible with 5.1)
end
return f
end
-- [*] http://lua-users.org/lists/lua-l/2010-06/msg00313.html
 
-- 5.1 style `getfenv` implemented in 5.2
function M.getfenv(f)
if f == 0 or f == nil then return _G end -- simulated behavior
local f = envhelper(f, 'setfenv')
local up, val = envlookup(f)
if not up then return _G end -- simulated behavior [**]
return val
end
-- [**] possible reasons: no _ENV upvalue, C function
end
 
 
return M
 
--[[ FILE rockspec.in
 
package = 'compat_env'
version = '$(_VERSION)-1'
source = {
url = 'https://raw.github.com/gist/1654007/$(GITID)/compat_env.lua',
--url = 'https://raw.github.com/gist/1654007/compat_env.lua', -- latest raw
--url = 'https://gist.github.com/gists/1654007/download',
md5 = '$(MD5)'
}
description = {
summary = 'Lua 5.1/5.2 environment compatibility functions',
detailed = [=[
Provides Lua 5.1/5.2 environment related compatibility functions.
This includes implementations of Lua 5.2 style `load` and `loadfile`
for use in Lua 5.1. It also includes Lua 5.1 style `getfenv` and `setfenv`
for use in Lua 5.2.
]=],
license = 'MIT/X11',
homepage = 'https://gist.github.com/1654007',
maintainer = 'David Manura'
}
dependencies = {} -- Lua 5.1 or 5.2
build = {
type = 'builtin',
modules = {
['compat_env'] = 'compat_env.lua'
}
}
 
--]]---------------------------------------------------------------------
 
--[[ FILE test.lua
 
-- test.lua - test suite for compat_env module.
 
local CL = require 'compat_env'
local load = CL.load
local loadfile = CL.loadfile
local setfenv = CL.setfenv
local getfenv = CL.getfenv
 
local function checkeq(a, b, e)
if a ~= b then error(
'not equal ['..tostring(a)..'] ['..tostring(b)..'] ['..tostring(e)..']')
end
end
local function checkerr(pat, ok, err)
assert(not ok, 'checkerr')
assert(type(err) == 'string' and err:match(pat), err)
end
 
-- test `load`
checkeq(load('return 2')(), 2)
checkerr('expected near', load'return 2 2')
checkerr('text chunk', load('return 2', nil, 'b'))
checkerr('text chunk', load('', nil, 'b'))
checkerr('binary chunk', load('\027', nil, 't'))
checkeq(load('return 2*x',nil,'bt',{x=5})(), 10)
checkeq(debug.getinfo(load('')).source, '')
checkeq(debug.getinfo(load('', 'foo')).source, 'foo')
 
-- test `loadfile`
local fh = assert(io.open('tmp.lua', 'wb'))
fh:write('return (...) or x')
fh:close()
checkeq(loadfile('tmp.lua')(2), 2)
checkeq(loadfile('tmp.lua', 't')(2), 2)
checkerr('text chunk', loadfile('tmp.lua', 'b'))
checkeq(loadfile('tmp.lua', nil, {x=3})(), 3)
checkeq(debug.getinfo(loadfile('tmp.lua')).source, '@tmp.lua')
checkeq(debug.getinfo(loadfile('tmp.lua', 't', {})).source, '@tmp.lua')
os.remove'tmp.lua'
 
-- test `setfenv`/`getfenv`
x = 5
local a,b=true; local function f(c) if a then return x,b,c end end
setfenv(f, {x=3})
checkeq(f(), 3)
checkeq(getfenv(f).x, 3)
checkerr('cannot change', pcall(setfenv, string.len, {})) -- C function
checkeq(getfenv(string.len), _G) -- C function
local function g()
setfenv(1, {x=4})
checkeq(getfenv(1).x, 4)
return x
end
checkeq(g(), 4) -- numeric level
if _G._VERSION ~= 'Lua 5.1' then
checkerr('unsupported', pcall(setfenv, 0, {}))
end
checkeq(getfenv(0), _G)
checkeq(getfenv(), _G) -- no arg
checkeq(x, 5) -- main unaltered
setfenv(function()end, {}) -- no upvalues, ignore
checkeq(getfenv(function()end), _G) -- no upvaluse
if _G._VERSION ~= 'Lua 5.1' then
checkeq(getfenv(setfenv(function()end, {})), _G) -- warning: incompatible with 5.1
end
x = nil
 
print 'OK'
 
--]]---------------------------------------------------------------------
 
--[[ FILE CHANGES.txt
0.2.20120124
Renamed module to compat_env (from compat_load)
Add getfenv/setfenv functions
 
0.1.20120121
Initial public release
--]]

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