Support lua 5.1 for `os.execute`

[jlaurens]

Due to https://tug.org/pipermail/luatex/2015-November/005536.html, penlight's utils.execute and utils.executeex are actually partially broken because they rely on version 5.3 of os.execute but luatex provides version 5.1.

[kalekje]

FWIW you can use lua(la)tex with 5.3: https://miktex.org/howto/lua53tex

[jlaurens]

Not really: using lua(la)tex with 5.3 is the problem.
In fact, latest luatex claims to implement lua 5.3 and penlight believes it.
But in reality, os.execute behaves like in lua 5.1, and that breaks penlight.

[kalekje]

Ah, thanks for clarifying. I am not the author of the lua library, I simply run a script to combine all files into one for ease of use with latex. I would recommend raising this issue here: https://github.com/lunarmodules/Penlight/issues

[jlaurens]

This is not a penlight issue. Pl is working well with pure lua 5.3. This is a texlua issue, but texlua developers do not want to make any change about that nor document this.
A warning note at the top of your flattened script would help as well as some documentation in the main README.md. I will see what I can do for that in a pair of days

[kalekje]

Do you have a work around (eg. replacement for os.execute) that works with 5.1? I'd be happy to update the documentation with a suggestion for a patch. It looks like os.execute is only referenced once in penlight.lua under compat.execute, so I'd only need to override one function.

[jlaurens]

What I used for myself is simply to define my own compat.execute assuming compat.lua51 is true. This is a copy/paste of the original code with little part properly commented out. I am not clear about the compat.jit52 part though.

function compat.execute(cmd)
    local res1,res2,res3 = os.execute(cmd)
    if res2 == "No error" and res3 == 0 and compat.is_windows then
      -- os.execute bug in Lua 5.2/5.3 not reporting -1 properly on Windows
      -- this was fixed in 5.4
      res3 = -1
    end
    if --[[compat.lua51 and]] not compat.jit52 then
        if compat.is_windows then
            return res1==0,res1
        else
            res1 = res1 > 255 and res1 / 256 or res1
            return res1==0,res1
        end
    else
        if compat.is_windows then
            return res3==0,res3
        else
            return not not res1,res3
        end
    end
end