Re: [PATCH v4 7/8] update-ref: support multiple simultaneous updates

[Junio C Hamano <gitster@pobox.com>]

Brad King <brad.king@kitware.com> writes:

> +With `--stdin`, update-ref reads instructions from standard input and
> +performs all modifications together.  Empty lines are ignored.
> +Each non-empty line is parsed as whitespace-separated arguments.

"whitespace-separated" implies that we may allow fields separated
with not a single SP, but with double SPs or even HTs between them.
I personally do not think we should be so loose; it is not like we
are allowing the user to type these from the terminal, so limiting
"separated by a single SP" may be perfectly adequate, and make it
less error prone (e.g. there will not be a confusion "Is 'A SP SP B'
A followed by B, or A followed by an empty string followed by B?").

> +Quote arguments containing whitespace as if in C source code.

Probably "as if they were strings in C source code".

> +Specify updates with lines of the form:
> +
> +	[--no-deref] [--] <ref> <newvalue> [<oldvalue>]
> +
> +Lines of any other format or a repeated <ref> produce an error.
> +Specify a zero <newvalue> to delete a ref and/or a zero <oldvalue>
> +to make sure that a ref not exist.  Use either 40 "0" or the
> +empty string (written as "") to specify a zero value.  Use `-z`
> +to specify input with no whitespace, quoting, or escaping, and
> +terminate each argument by NUL and each line by LF NUL.

This is a somewhat interesting choice of the record terminator. Do
we have a precedent to use LF NUL elsewhere?  If this is the first
such case where we need to express variable number of NUL-separated
fields in a record, I think I am fine with LF NUL (but I am sure
other people would give us a better convention if we ask them
politely ;-)), but I just want to make sure we do it the same way as
other codepaths, if exist, that have to handle this kind of thing.