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From: Jeff King <>
To: Emily Shaffer <>
Cc: "brian m. carlson" <>,
	Git List <>, Jonathan Nieder <>,
	Jose Lopes <>,
	Aleksandr Mikhailov <>
Subject: Re: Proposal/Discussion: Turning parts of Git into libraries
Date: Wed, 22 Feb 2023 14:34:31 -0500	[thread overview]
Message-ID: <Y/> (raw)
In-Reply-To: <>

On Fri, Feb 17, 2023 at 02:49:51PM -0800, Emily Shaffer wrote:

> > Personally, I'd like to see some sort of standard error type (whether
> > integral or not) that would let us do more bubbling up of errors and
> > less die().  I don't know if that's in the cards, but I thought I'd
> > suggest it in case other folks are interested.
> Yes!!! We have talked about this a lot internally - but this is one
> thing that will be difficult to introduce into Git without making
> parts of the codebase a little uglier. Since obviously C doesn't have
> an intrinsic to do this, we'll have to roll our own, which means that
> manipulating it consistently at function exits might end up pretty
> ugly. So hearing that there's interest outside of my team to come up
> with such a type makes me optimistic that we can figure out a
> neat-enough solution.

Here are some past discussions on what I thought would be a good
approach to error handling. The basic idea is to replace the "pass a
strbuf that people shove error messages into" approach with an error
context struct that has a callback. And that callback can then stuff
them into a strbuf, or report them directly, or even die.

This thread sketches out the idea, though sadly I no longer have the
more fleshed-out patches I mentioned there:

And then the sub-thread starting here discusses a similar approach:

It does mean passing a "struct error_context" just about everywhere.
Though since the context doesn't change very much and most calls are
just forwarding it along, it would probably also be reasonable to have a
thread-local global context, and push/pop from it (sort of a poor man's
dynamic scoping).

One thing that strategy doesn't help with, though, that your
libification might want: it's not very machine-readable. The error
reporters would still fundamentally be working with strings. So a
libified process can know "OK, writing this ref failed, and I have some
error messages in a buffer". But the calling code can't know specifics
like "it failed because we tried to open file 'foo' and it got EPERM".
We _could_ design an error context that stores individual errno values
or codes in a list, but having each caller report those specific errors
is a much bigger job (and ongoing maintenance burden as we catalogue and
give an identifier to each error).


  reply	other threads:[~2023-02-22 19:34 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-17 21:12 Proposal/Discussion: Turning parts of Git into libraries Emily Shaffer
2023-02-17 21:21 ` brian m. carlson
2023-02-17 21:38   ` Emily Shaffer
2023-02-17 22:41     ` brian m. carlson
2023-02-17 22:49       ` Emily Shaffer
2023-02-22 19:34         ` Jeff King [this message]
2023-02-24 20:31           ` Emily Shaffer
2023-02-24 21:41             ` Jeff King
2023-02-24 22:59             ` Junio C Hamano
2023-02-17 22:04   ` rsbecker
2023-02-17 22:48     ` brian m. carlson
2023-02-17 22:57 ` Junio C Hamano
2023-02-18  1:59   ` demerphq
2023-02-18 10:36     ` Phillip Wood
2023-03-23 23:22       ` Felipe Contreras
2023-03-23 23:30         ` rsbecker
2023-03-23 23:34           ` Felipe Contreras
2023-03-23 23:42             ` rsbecker
2023-03-23 23:55               ` Felipe Contreras
2023-03-24 19:27                 ` rsbecker
2023-03-24 21:21                   ` Felipe Contreras
2023-03-24 22:06                     ` rsbecker
2023-03-24 22:29                       ` Felipe Contreras
2023-02-21 21:42   ` Emily Shaffer
2023-02-22  0:22     ` Junio C Hamano
2023-02-18  4:05 ` Elijah Newren
2023-02-21 22:06   ` Emily Shaffer
2023-02-22  8:23     ` Elijah Newren
2023-02-22 19:25     ` Jeff King
2023-02-21 19:09 ` Taylor Blau
2023-02-21 22:27   ` Emily Shaffer
2023-02-22  1:44 ` Victoria Dye
2023-02-25  1:48   ` Jonathan Tan
2023-02-22 14:55 ` Derrick Stolee
2023-02-24 21:06   ` Emily Shaffer
2023-03-23 23:37 ` Felipe Contreras
2023-03-23 23:44   ` rsbecker

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