Backwards compatibility (was Re: how can you tell you have merged?)

[Bill Barry]

Adrian Buehlmann wrote:
> On 11.09.2008 21:24, Matt Mackall wrote:
>   
>> I would really appreciate it if people who are not new here would
>> refrain from suggesting changes that break backwards compatibility.
>> We can't change the default output of status, it will kill dozens of
>> innocent programs including people's build systems and IDEs. Such
>> changes are categorically off-limits and I'm growing quite weary of
>> pointing that out (it feels like it's a daily occurrence).
>>     
>
> One root of this problem probably is that it would have been
> better if Mercurial would have separated the two use case
> categories:
> (1) tools using hg on the command line and (2) real users
> interacting with hg directly on the command line.
>
> Also, a couple of tools have to use Mercurial via the command
> line only because of license incompatibilities.
>
> But yes, even *I* am aware that that ship has sailed.
>
> We are now restricted with the command line interface by
> the tools that already depend on it.
>   
Isn't this what the major version number is for (not that I am saying 
that such a small change like that addition to status warrants it, or 
that it should be done any time remotely soon; I've got several programs 
dependent on the CLI)?

Everything can be calculated as risk:
Are the changes to the API more beneficial to have than the cost of 
modifying whatever unknown programs which might be dependent on the 
current API (In the vast majority of current change requests, this is a 
resounding NO).

Perhaps at some point it might be worth considering planned API breakage 
(probably Matt would be the first to suggest it if the time came, 
somebody always has to look out for the long term of a project, and that 
person seems like Matt here).

*** (I don't want any changes now, or any time in the near future; as of 
right now I don't even have an imagination for any such possibilities)


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