Re: [PATCH 2/2] config: allow specifying config entries via envvar pairs

On Tue, Nov 17 2020, Jeff King wrote:

On Mon, Nov 16, 2020 at 11:39:35AM -0800, Junio C Hamano wrote:

quoted

quoted

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While not document, it is currently possible to specify config entries
[in GIT_CONFIG_PARAMETERS]

[...]

"While not documented" yes, for sure, but we do not document it for
a good reason---it is a pure implementation detail between Git
process that runs another one as its internal implementation detail.

I have actually been quite tempted to document and promise that it will
continue to work. Because it really is useful in some instances. The
thing that has held me back is that the documentation would reveal how
unforgiving the parser is. ;)

It insists that key/value pairs are shell-quoted as a whole. I think if
we made it accept a some reasonable inputs:

  - do not require quoting for values that do not need it

  - allow any amount of shell-style single-quoting (whole parameters,
    just values, etc).

  - do not bother allowing other quoting, like double-quotes with
    backslashes. However, document backslash and double-quote as
    meta-characters that must not appear outside of single-quotes, to
    allow for future expansion.

then I'd feel comfortable making it a public-facing feature. And for
most cases it would be pretty pleasant to use (and for the unpleasant
ones, I'm not sure that a little quoting is any worse than the paired
environment variables found here).

I wonder if something like the git config -z format wouldn't be easier,
with the twist that we'd obviously not support \0. So we'd need an
optional length prefix. : = unspecified.

    :user.name
    Jeff K
    :alias.ci
    commit
    :10:bin.ary
    <10 byte string, might have a \n>
    :other.key
    Other Value

Maybe that's overly fragile, or maybe another format would be better. I
was trying to come up with one where the common case wouldn't require
knowing about shell quoting/unquoting, and where you could still do:

    GIT_CONFIG_PARAMETERS=":my.new\nvalue\n$GIT_CONFIG_PARAMETERS"

Or equivalent, and still just keep $GIT_CONFIG_PARAMETERS as-is to pass
it along.

Your "do not require quoting" accomplishes that, and it's arguably a lot