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

[Sergey Kaplun via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Igor,

On 07.04.21, Igor Munkin wrote:
> 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.

I mean that this behaviour is verificated by the test. When behaviour is
changed the test is changed too.

> 
> > 
> > > What does "fully reversible" mean in this context?
> 
> This question is left unaddressed.

I don't know what does Mike mean by these.

> 
> > > 
> > > 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?

Don't get you point here. AFAIU it means that `%q` is the only one
option that can contain embeded zeros, so it handles it in the special
way.

> 
> > 
> > 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.

I am talking about this part:

| Character class %z in patterns is deprecated, as now patterns may
| contain '\0' as a regular character.

> 
> > 
> 
> <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

-- 
Best regards,
Sergey Kaplun