Re: ds/maintenance-part-3 (was Re: What's cooking in git.git (Nov 2020, #02; Mon, 9))

[Emily Shaffer <emilyshaffer@google.com>]

On Tue, Nov 17, 2020 at 08:56:16AM -0500, Derrick Stolee wrote:
> 
> On 11/16/2020 8:07 PM, Emily Shaffer wrote:
> > On Mon, Nov 16, 2020 at 04:40:35PM -0800, Junio C Hamano wrote:
> >>
> >> Emily Shaffer <emilyshaffer@google.com> writes:
> >>
> >>> Because 'git maintenance unregister' spins a child process to call 'git
> >>> config --unset maintenance.repo <cwd>', it actually fails if "cwd"
> >>> contains a POSIX regular expression special character:
> >>>
> >>>   git config [<file-option>] --unset name [value_regex]
> >>
> >> Good find.  And it is even worse that value_regex uses ERE, not BRE,
> >> which means even an otherwise innocuous letter like '+' cannot be
> >> used without quoting.
> > 
> > I should have mentioned in the first letter than Jonathan Nieder was the
> > one who made the jump from "this is breaking in the buildbot but not
> > locally" to regular expression metachars. Credit where it's due.
> 
> Thank you for finding and reporting this bug.
> 
> Can I at least have a short moment of griping about anyone putting
> regex characters into their directory names? ;)

In this case the directory name contained 'git-2.29.2+next.20201112' -
so I'll leave it up to you to decide ;) ;)

> 
> >>> You can demo it for yourself like so:
> >>>
> >>>   git init repro+for+maintenance
> >>>   git maintenance register
> >>>   git maintenance unregister
> >>>   echo $?	# returns '5'
> >>>   git config --list --global
> >>>
> >>> I see two paths forward:
> >>>
> >>
> >> 0. Quote the value_regex properly, instead of blindly using a value
> >>    that comes from the environment.
> 
> Pulling the subcommand from my test enfironment using GIT_TRACE2_PERF=1
> I see the following quotes being used:
> 
> git config --global --unset maintenance.repo "/repos/new+repo*test"
> 
> I'm guessing that what we really want is to _escape_ the regex glob
> characters? This command works:
> 
> git config --global --unset maintenance.repo "/repos/new\+repo\*test"
> 
> The only place I see where we do that currently is in
> builtin/sparse-checkout.c:escaped_pattern(). Please let me know if
> you know of a more suitable way to escape regex characters.
> 
> >>> 1. Teach 'git config' to learn either which regex parser to use
> >>> (including fixed), or at least to learn "value isn't a regex", or
> >>>
> >>> 2. Don't spin a child process in 'git maintenance [un]register' and
> >>> instead just call the config API.
> >>
> >>> I'd suggest #2. The config API is very nice, and seems to have a simple
> >>> way to add or remove configs to your global file in just a couple of
> >>> lines. If there's a reason why it's not simpler to do it that way, it's
> >>> my fault for missing the review :)
> >>
> >> My short-to-mid-term preference is to do #1 to allow a value to be
> >> spelled literally (i.e. remove entry with _this_ value, and add this
> >> one instead), and optionally do #2 as an optimization that is not
> >> essential.  I do not offhand know how you can make #2 alone fly
> >> without doing some form of #1, as I think the same value_regex that
> >> ought to be ERE to specify entries to be replaced needs to be used
> >> under the cover even if you use "config API" anyway.
> > 
> > Ah, right you are - I had figured the regex parsing was done earlier,
> > but it indeed looks to happen in
> > config.c:git_config_set_multivar_in_file_gently. Thanks.
> 
> So the "real fix" is to allow a command-line option to 'git config'
> that makes the "value_regex" parameter a literal string? Of course,
> this would either require wiring an option down into
> git_config_set_multivar_in_file_gently() to treat the string as a
> literal _or_ to escape the input string in builtin/config.c.
> 
> Am I understanding the intended plan here?

That fix sounds like something I would want anyways - the ability to
choose the regex style just like we can for 'git grep' (and I think for
other tools which I'm having trouble finding now).

 - Emily