Re: [PATCH 0/5] promise: introduce promises to track success or error

Patrick Steinhardt [off-list ref] writes:

While we're already at it throwing ideas around, I also have to wonder
whether this would be a long-term solution towards computer-friendly
errors. One of the problems we quite frequently hit in Gitaly is that we
are forced to parse error messages in order to figure out why exactly
something has failed. Needless to say, this is quite fragile and also
feels very wrong.

Now if we had a more structured way to pass errors around this might
also enable us to convey more meaning to the caller of Git commands. In
a hypothetical world where all errors were using an explicit error type,
then this error type could eventually become richer and contain more
information that is relevant to the calling script. And if such rich
error information was available, then it would not be that far fetched
to ask Git to emit errors in a computer-parsable format like for example
JSON.

I do not know about the "JSON-parseable" part, but a structured
error message, or even just a set of error codes that can be
recorded in an index, might already be a great improvement.