Re: [PATCH 00/10] [RFC] In-tree sparse-checkout definitions

From: Elijah Newren <newren@gmail.com>
To: Derrick Stolee <stolee@gmail.com>
Cc: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>,
	Git Mailing List <git@vger.kernel.org>, Jeff King <peff@peff.net>,
	Taylor Blau <me@ttaylorr.com>,
	Jonathan Nieder <jrnieder@gmail.com>,
	Derrick Stolee <dstolee@microsoft.com>
Subject: Re: [PATCH 00/10] [RFC] In-tree sparse-checkout definitions
Date: Wed, 17 Jun 2020 18:59:27 -0700	[thread overview]
Message-ID: <CABPp-BFDcM+QSx_YSAAazkN9AoTPWVYV+ZpSQBPTihVM=gP-qw@mail.gmail.com> (raw)
In-Reply-To: <64d477b6-7bf2-fa0d-b9b4-821285af386e@gmail.com>

On Wed, Jun 17, 2020 at 6:42 PM Derrick Stolee <stolee@gmail.com> wrote:
>
> On 6/17/2020 7:14 PM, Elijah Newren wrote:
> > Hi,
> >
> > Another late addition...
> >
> > On Thu, May 7, 2020 at 6:20 AM Derrick Stolee via GitGitGadget
> > <gitgitgadget@gmail.com> wrote:
> >
> >> IN-TREE SPARSE-CHECKOUT DEFINITIONS
> >> ===================================
> >>
> >> Minh's idea was simple: have sparse-checkout files in the working directory
> >> and use config to point to them. As these in-tree files update, we can
> >> automatically update the sparse-checkout definition accordingly. Now, the
> >> only thing to do would be to ensure that the sparse-checkout files are
> >> updated when someone updates the build definitions. This requires some extra
> >> build validation, but would not require special tools built on every client.
> >
> > "In-tree" still bugs me after a few weeks; the wording seems slightly
> > awkward.  I don't have a good suggestion, but I'm curious if there's a
> > better term.
>
> I am open to suggestions. It reminds me of the two hardest problems
> in software engineering:
>
>         1. concurrency
>         2. naming things
>         3. off-by-one errors

:-)

> > But I really came here to comment on another issue I think I glossed
> > over the first time around.  I'm curious if all module definition
> > files have to exist in the working directory, as possibly suggested
> > above, or if we can allow them to just exist in the index.  To give
> > you a flavor for what I mean, with my sparsify tool people can do
> > things like:
> >     ./sparsify --modules MODULE_A
> > which provides MODULE_A and it's dependencies while removing all other
> > directories.  If MODULE_B, is not a dependency (direct or transitive)
> > of MODULE_A, it will not exist in the working directory after this
> > step.  Our equivalent of the "in-tree" definition of MODULE_B exists
> > *in* the directory for MODULE_B, because it seems to make sense for
> > us.  I want people to be able to do
> >     ./sparsify --modules MODULE_B
> > and have it correctly check out all the necessary files even though
> > the definition of MODULE_B wasn't even in the working directory at the
> > time the command ran.  (The sparsify script knows to check the working
> > directory first, then fall back to the index).
>
> I think one tricky part of my RFC is that it _only_ looks at the
> index. This allows us to read the contents even when the files are
> not part of the current sparse-checkout definition.
>
> You mentioned in another thread that it is a bit unwieldy for a user
> to rely on a committed (or staged?) file, so adding the ability to
> check the working directory first is interesting. I wonder how the
> timing comes into play when changing HEAD to a new commit? Seems
> tricky, but solvable.

Isn't that essentially the same timing issue that comes into play if
you only look at the index, and are changing HEAD to a new commit?