Re: [Tarantool-patches] [PATCH v2 luajit 16/30] test: adapt PUC Lua test for %q in fmt for LuaJIT

[Igor Munkin via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Sergey,

On 01.04.21, Sergey Kaplun wrote:
> Igor,
> 
> Thanks for the review!
> 
> On 31.03.21, Igor Munkin wrote:
> > Sergey,
> > 

<snipped>

> > 
> > > string.format(): %q reversible.
> > > See also https://luajit.org/extensions.html#lua52.
> > > 
> > > In Lua 5.1 string.format() does not accept string values containing
> > > embedded zeros, except as arguments to the '%q' option.
> > > In Lua 5.2 '\0' is not handled differently from other
> > > control chars in string.format('%q', ...).
> > > See commit 7cc981c14067d4b0e774a6bfb0acfc2f5c911f0d
> > > (string.format("%q", str) is now fully reversible
> > > (from Lua 5.2).).
> > 
> > Well, I honestly don't understand what is changed in *semantics*. I've
> > tried the following command with Lua 5.2, Lua 5.1 and LuaJIT 2.0.5 as an
> > interpreter being tested
> > | <interp> -e 'print(string.format("%q", "\0"))'
> > 
> > I understand the semantics of "%q", but was it just a bug in Lua 5.1?
> 
> A bug with the test for it???

Well, I can remind you the bug with <tonumber> we fixed the last year.
There might be no test for it though, but all in all it has not been
fixed in Lua 5.1.

> 
> > What does "fully reversible" mean in this context?

This question is left unaddressed.

> > 
> > I understand only the fact the behaviour differs and you reimplemented
> > the test assertion according to Lua 5.2 testing suite. That's all.
> > 
> > I found not a single word regarding this issue in Lua bugs[1] page,
> > except invalid handling of \r[2]. Is there any issue/page with a more
> 
> It looks unrelated to these changes.
> 
> > verbose explanation what has been changed in 7cc981c?
> 
> I just read these lines in Lua 5.1 reference manual :):
> | This function does not accept string values containing embedded
> | zeros, except as arguments to the q option.

So what? This means literally nothing to me... BTW, I can pass such
string to the function and it can yield any bullshit the developer
wanted to. That's why we decided to comment such places in a clear and
verbose way, didn't we?

> 
> As for me, it is just new behaviour of Lua 5.2 -- patterns now accept
> '\0' as a reqular character (see
> 4541243355a299a9b75042d207feb87295872c3a (patterns now accept '\0' as a
> regular character) from Lua repository). So, according to commit
> 658ea8752b979102627e2fede7b7ddfbb67ba6c9 (no need to handle '\0'
> differently from other control chars in format '%q')) from Lua
> repository, this behaviour is excess.
> 
> Also, it is mentioned here [2].

I see nothing regarding this change there.

> 

<snipped>

> > 
> > [1]: https://www.lua.org/bugs.html#5.1
> > [2]: https://www.lua.org/bugs.html#5.1-4
> > 
> > -- 
> > Best regards,
> > IM
> 
> [1]: https://www.lua.org/manual/5.1/manual.html#pdf-string.format
> [2]: https://www.lua.org/manual/5.2/manual.html#8.2
> 
> -- 
> Best regards,
> Sergey Kaplun

-- 
Best regards,
IM