provide math functions deprecated by the lack of LUA_COMPAT_MATHLIB on Lua 5.5

[luau-project]

Description

From Lua 5.2.0 up to Lua 5.4.8, the presence of several deprecated functions in the mathematical library are controlled by a few macros, turned on by default (via CFLAGS) in the released src/Makefile:

• Lua 5.2: the macro LUA_COMPAT_ALL is turned on by default by

  CFLAGS= -O2 -Wall -DLUA_COMPAT_ALL $(SYSCFLAGS) $(MYCFLAGS)

• Lua 5.3: the macro LUA_COMPAT_5_2 is turned on by default by

  CFLAGS= -O2 -Wall -Wextra -DLUA_COMPAT_5_2 $(SYSCFLAGS) $(MYCFLAGS)

• Lua 5.4: the macro LUA_COMPAT_5_3 is turned on by default by

  CFLAGS= -O2 -Wall -Wextra -DLUA_COMPAT_5_3 $(SYSCFLAGS) $(MYCFLAGS)

However, on Lua 5.5, even though the macro LUA_COMPAT_MATH is able to keep such deprecated functions in the mathematical library, this macro has been turned off in both src/Makefile and src/luaconf.h:

• src/Makefile: CFLAGS= -O2 -Wall -Wextra $(SYSCFLAGS) $(MYCFLAGS)
• src/luaconf.h: see https://github.com/lua/lua/blob/a5522f06d2679b8f18534fd6a9968f7eb539dc31/luaconf.h#L344-L352

Conclusion

Even though I'm not sure whether it is the role of lua-compat53 to backport such functions as a compatibility layer, but since these functions are turned on a standard Lua 5.2 - Lua 5.4 build, I think such funcs could be easily provided by lua-compat53 to keep compatibility at
https://github.com/lunarmodules/lua-compat-5.3/blob/9c6f75a88db1462ff655dc006588b25d3bc2a5be/compat53/module.lua

Note

I could try to help with a PR if there's interest.

[daurnimator]

the presence of several deprecated functions in the mathematical library

My first thought was "which functions is that" to which I'll link to https://github.com/lua/lua/blob/a5522f06d2679b8f18534fd6a9968f7eb539dc31/lmathlib.c#L730-L737

  {"atan2", math_atan},
  {"cosh",   math_cosh},
  {"sinh",   math_sinh},
  {"tanh",   math_tanh},
  {"pow",   math_pow},
  {"log10", math_log10},

[luau-project]

@daurnimator thank you for the heads up! I totally missed that info.

Expanding on daurnimator comment, let me add a few more (important) details:

1. the list of deprecated math functions varies every minor Lua release:

   • Lua 5.2: see https://github.com/lua/lua/blob/e2fc2ce8dfe107d1e2742b459c2aaf137227bbc1/lmathlib.c#L252-L254

     #if defined(LUA_COMPAT_LOG10)
       {"log10", math_log10},
     #endif

   • Lua 5.3: see https://github.com/lua/lua/blob/75ea9ccbea7c4886f30da147fb67b693b2624c26/lmathlib.c#L376-L385

     #if defined(LUA_COMPAT_MATHLIB)
       {"atan2", math_atan},
       {"cosh",   math_cosh},
       {"sinh",   math_sinh},
       {"tanh",   math_tanh},
       {"pow",   math_pow},
       {"frexp", math_frexp},
       {"ldexp", math_ldexp},
       {"log10", math_log10},
     #endif

   • Lua 5.4: see https://github.com/lua/lua/blob/6e22fedb74cf0c9b6656e9fce8b7331db847c605/lmathlib.c#L744-L753

     #if defined(LUA_COMPAT_MATHLIB)
       {"atan2", math_atan},
       {"cosh",   math_cosh},
       {"sinh",   math_sinh},
       {"tanh",   math_tanh},
       {"pow",   math_pow},
       {"frexp", math_frexp},
       {"ldexp", math_ldexp},
       {"log10", math_log10},
     #endif

   • Lua 5.5: see https://github.com/lua/lua/blob/a5522f06d2679b8f18534fd6a9968f7eb539dc31/lmathlib.c#L730-L737

     #if defined(LUA_COMPAT_MATHLIB)
       {"atan2", math_atan},
       {"cosh",   math_cosh},
       {"sinh",   math_sinh},
       {"tanh",   math_tanh},
       {"pow",   math_pow},
       {"log10", math_log10},
     #endif

2. On Unix systems, we usually employ src/Makefile to drive the build. Using the provided src/Makefile, such functions are available due the CFLAGS from Lua 5.2.0 to Lua 5.4.8 in a standard build.

Important

However, on Windows, there isn't a standard manner to build Lua using GCC incompatible compilers (e.g.: MSVC). Through different compiler toolchains, we have to build Lua ourselves, usually from the command line. Building Lua ourselves on different systems often produces an interpreter (lua or lua.exe) with different settings. For instance, at the moment, the two most popular GitHub Actions to install Lua (leafo/gh-actions-lua and luarocks/gh-actions-lua) do not enable compatibility macros on any Lua version during the build employing the MSVC toolchain. This means that, usually, Lua on Windows (5.2 or newer) built with MSVC does not ship with the same math functions as seen on Unix.

Final thoughts

So, my proposal is: provide the largest list of deprecated math functions (e.g.: seen on Lua 5.3), and make them available in the Lua side (sample code):

local M = require("compat53.module")

-- add a backport for each deprecated math function
-- in the spirit of math.log10. Of course, this
-- is just the skeleton of the (untested) idea.
-- The final version would be discussed in details
-- in a subsequent PR.

local log10 = M.math.log10 or function(x) return math.log(x, 10) end

if lua_version >= "5.2" then
    if not M.math.log10 then
        M.math.log10 = log10
    end
end