[João Valverde <joao.valverde@xxxxxxxxxxxxxxxxxx>]

On 08/19/2016 04:18 PM, Pascal Quantin wrote:
> 2016-08-19 17:05 GMT+02:00 Jo�o Valverde
> <joao.valverde@xxxxxxxxxxxxxxxxxx
> <mailto:joao.valverde@xxxxxxxxxxxxxxxxxx>>:
>
>
>
>     On 08/19/2016 03:56 PM, Jo�o Valverde wrote:
>
>
>
>         On 08/19/2016 02:54 PM, Peter Wu wrote:
>
>             On Mon, Aug 08, 2016 at 09:17:35PM +0100, Jo�o Valverde wrote:
>
>
>
>                 On 08/08/2016 05:58 PM, Pascal Quantin wrote:
>
>                     Hi Jo�o,
>
>                     2016-08-08 18:52 GMT+02:00 Jo�o Valverde
>                     <joao.valverde@xxxxxxxxxxxxxxxxxx
>                     <mailto:joao.valverde@xxxxxxxxxxxxxxxxxx>
>                     <mailto:joao.valverde@xxxxxxxxxxxxxxxxxx
>                     <mailto:joao.valverde@xxxxxxxxxxxxxxxxxx>>>:
>
>                         Is moving to Lua 5.3 something we should look into?
>
>                         The 64 bit integer support seems really promising.
>
>
>                     Hariel explained us that Lua 5.3 was a completely
>                     different language (a
>                     bit like what you have between Python 2.X and 3.X).
>                     You can find much
>                     more info (from people knowing what they are taling
>                     about - so not me
>                     ;)) in bug 10881.
>
>                     Pascal.
>
>
>
>                 Thanks for that Pascal. The only sane way to approach
>                 the issue IMHO
>                 is to
>                 accept that this may and probably will break backward
>                 compatibility (not
>                 even think about supporting 5.1 or 5.2) and just
>                 consider whether
>                 that break
>                 is justified (hint: it is).
>
>
>             Why is it justified to break backwards compatibility and
>             move from 5.2
>             to 5.3 without the ability to chose for 5.2? What is the
>             killer feature
>             of 5.3 that makes it totally worth to possibly break older
>             dissectors?
>
>             The disadvantage of C plugins is that it had to be
>             recompiled for newer
>             versions. With a move from 5.2 to 5.3 and also removing
>             GRegex and bitop
>             you make it quite likely to break Lua dissectors in some way.
>
>             I have once written a Lua library in C, interfacing with
>             Libgcrypt for
>             which I studied the Lua manual. The API changes with 5.3
>             were not that
>             significant if I remember correctly (though you have to be
>             careful with
>             providing a compatibility layer), but the ABI is certainly not
>             compatible.
>
>             In the recent proposed patches, you seem to have no issues
>             with breaking
>             backwards compatibility. Have you developed Lua dissectors
>             before?
>             Breaking things for the sake of "shiny, new, future" is not an
>             acceptable motivation, there must be something more
>             appealing to justify
>             such breakage. Having 64-bit integer support, but taking
>             away the bitop
>             library is a net loss without even considering the other
>             factors.
>
>
>         Doesn't Lua 5.3 provide native bit operators? If so there is not net
>         loss of functionality. That was my reasoning at least.
>
>         The language incompatibilities between 5.2 and 5.3 are minor. The
>         wireshark API is exactly the same.
>
>         LPeg is more powerful and Lua-thonic than lrexlib, but there is a
>         learning curve for that, no doubt. For anyone relying on
>         lrexlib, it's a
>         significant break. We can keep lrexlib, that's not a problem and
>         it is
>         orthogonal to the other changes.
>
>         As far as killer features go, besides the obvious, how about better
>         UTF-8 support?
>
>         I don't have time for a more detailed answer right now but I'd
>         like to
>         say I think this change is entirely justified but I also completely
>         understand disagreeing with that opinion.
>
>
>     I'm referring to the upgrade to Lua 5.3 here, i.e, breaking backward
>     compatibility, same as any other Lua script moving from 5.1/5.2 to 5.3.
>
>
> For what it is worth, I do not remember any user asking / pushing to
> upgrade to Lua 5.3 yet. Breaking their script should be justified by a
> huge win (I will not judge myself whether this is the case or not with
> this upgrade as I'm not a Lua user, so I'm not qualified here; but we
> must think about our existing users). C plugins are a bit of main to
> recompile for each version, but are fast. ON the other side Lua scripts
> were not as impacted as C ones with API changes, but are slower (from
> what I understood). Any big change here should be done with caution I think.

I think the impact is very small compared to the benefits, it's an easy 
port to Lua 5.3 if it requires porting at all, but maybe someone else 
who uses this code heavily can comment on that.

I really like the Wireshark Lua API, by the way. It's really cool.