Re: Proposal/Discussion: Turning parts of Git into libraries

[Felipe Contreras <felipe.contreras@gmail.com>]

On Thu, Mar 23, 2023 at 5:43 PM <rsbecker@nexbridge.com> wrote:
>
> On Thursday, March 23, 2023 7:35 PM, Felipe Contreras wrote:
> >On Thu, Mar 23, 2023 at 5:30 PM <rsbecker@nexbridge.com> wrote:
> >>
> >> On Thursday, March 23, 2023 7:22 PM, Felipe Contreras wrote:
> >> >On Sat, Feb 18, 2023 at 5:12 AM Phillip Wood <phillip.wood123@gmail.com>
> >wrote:
> >> >>
> >> >> On 18/02/2023 01:59, demerphq wrote:
> >> >> > On Sat, 18 Feb 2023 at 00:24, Junio C Hamano <gitster@pobox.com> wrote:
> >> >> >>
> >> >> >> Emily Shaffer <nasamuffin@google.com> writes:
> >> >> >>
> >> >> >>> Basically, if this effort turns out not to be fruitful as a
> >> >> >>> whole, I'd like for us to still have left a positive impact on the codebase.
> >> >> >>> ...
> >> >> >>> So what's next? Naturally, I'm looking forward to a spirited
> >> >> >>> discussion about this topic - I'd like to know which concerns
> >> >> >>> haven't been addressed and figure out whether we can find a way
> >> >> >>> around them, and generally build awareness of this effort with the
> >community.
> >> >> >>
> >> >> >> On of the gravest concerns is that the devil is in the details.
> >> >> >>
> >> >> >> For example, "die() is inconvenient to callers, let's propagate
> >> >> >> errors up the callchain" is an easy thing to say, but it would
> >> >> >> take much more than "let's propagate errors up" to libify
> >> >> >> something like
> >> >> >> check_connected() to do the same thing without spawning a
> >> >> >> separate process that is expected to exit with failure.
> >> >> >
> >> >> >
> >> >> > What does "propagate errors up the callchain" mean?  One
> >> >> > interpretation I can think of seems quite horrible, but another
> >> >> > seems quite doable and reasonable and likely not even very
> >> >> > invasive of the existing code:
> >> >> >
> >> >> > You can use setjmp/longjmp to implement a form of "try", so that
> >> >> > errors dont have to be *explicitly* returned *in* the call chain.
> >> >> > And you could probably do so without changing very much of the
> >> >> > existing code at all, and maintain a high level of conceptual
> >> >> > alignment with the current code strategy.
> >> >>
> >> >> Using setjmp/longjmp is an interesting suggestion, I think lua does
> >> >> something similar to what you describe for perl. However I think
> >> >> both of those use a allocator with garbage collection. I worry that
> >> >> using longjmp in git would be more invasive (or result in more
> >> >> memory leaks) as we'd need to to guard each allocation with some
> >> >> code to clean it up and then propagate the error. That means we're
> >> >> back to manually propagating errors up the call chain in many cases.
> >> >
> >> >We could just use talloc [1].
> >>
> >> talloc is not portable.
> >
> >What makes you say that?
>
> talloc is not part of a POSIX standard I could find.

It's a library, like: z, ssl, curl, pcre2-8, etc. Libraries can be
compiled on different platforms.

-- 
Felipe Contreras