Re: RFC: error codes on exit

[Jeff King <peff@peff.net>]

On Thu, May 20, 2021 at 10:47:38AM -0700, Jonathan Nieder wrote:

> >                 And that gets very daunting to think about annotating
> > and communicating about each such case (we don't even pass that level of
> > detailed information inside the program in a machine-readable way;
> > scraping stderr is the best way to figure this stuff out now).
> 
> This feels like good news to me: it sounds like if we add
> application-specific codes like MISSING_OBJECT to Git, then it would
> be useful to both of us.

Perhaps. I think the context matters between "missing an object from the
command line" and "missing an object I expected to find while
traversing". And I'm not sure all spots which look up an object will
know that context.

In some sense that's "just" a programming problem; surfacing the errors
to the right spot that can decide how to exit. But I worry a bit that
it's fighting uphill against the current code structure. There's
probably going to be a period where MISSING_OBJECT versus UNKNOWN is
wildly inaccurate, and a long tail of cases to fix.

Erring to say "UNKNOWN" is probably OK for most callers (they are happy
to learn of a specific error and act on it appropriately, but if Git
can't tell it to them, they have a generic path). But erring in the
other direction might be bad (you fail to realize a repo is corrupt, and
instead attribute it to caller error).

So again, I return "I dunno". Something of this magnitude probably has
to be done incrementally and over time. But I'd be loathe to trust it
and convert existing callers use it for a while. And that creates a
chicken-and-egg problem for finding the places which need improvement.

-Peff