From: Jay Soffian <jaysoffian@gmail.com>
Date: Thu, 22 Sep 2011 18:41:42 GMT
Subject: Re: How to use git attributes to configure server-side checks?
Message-ID: <CAG+J_DxdP2qHhttJOtWQTKeiDV2YbC_A_F+b9sDOZsWhWxjcjw@mail.gmail.com>
In-Reply-To: <20110922171340.GA2934@sigill.intra.peff.net>

On Thu, Sep 22, 2011 at 1:13 PM, Jeff King <peff@peff.net> wrote:
>
> No, we definitely don't use in-tree gitattributes. IIRC, there are some
> precedence and ordering questions. I think the ordering now is:
>
>  1. Look in $GIT_DIR/info/attributes
>
>  2. If not found, look in per-directory .gitattributes
>
>  3. If not found, look in core.gitattributesfile
>
> Where do in-tree attributes fit in? Between 1 and 2? Or 2 and 3? And
> which tree do we look at?

attr.c says:

  a. built-in attributes
  b. $(prefix)/etc/gitattributes unless GIT_ATTR_NOSYSTEM is set
  c. core.attributesfile
  d. per-directory .gitattributes
  e. $GIT_DIR/info/attributes

The mechanics of (d) are established by git_attr_direction:

  GIT_ATTR_CHECKIN: working-copy, then index
  GIT_ATTR_CHECKOUT: index, then working-copy
  GIT_ATTR_INDEX: index-only

Where GIT_ATTR_CHECKIN is the default direction and GIT_ATTR_CHECKOUT
is used while checking-out files from the index. (GIT_ATTR_INDEX is
used only by git-archive.)

Note that (d) only occurs in non-bare repos or if direction is GIT_ATTR_INDEX.

> Here are some examples:
>
>  a. If I do "git checkout branch-foo", we should look at branch-foo's
>     tree for things like crlf, right?  Do we still fall back to
>     per-directory .gitattributes in the working tree? On the one hand,
>     they're not really relevant to the commit we're moving to. But they
>     are respected in the current code, and can be useful when moving to
>     old commits which lack attributes.
>
>     I think this is where the index magic comes in in the current code
>     (we do something like "load the index, then respect gitattributes
>     from the index").
>
>     So maybe this is solved already.
>
>  b. You're diffing commit $a against commit $b. Whose gitattributes
>     have precedence? Is order important? Are gitattributes in the
>     working tree and index relevant?
>
>  c. You're diffing commit $a against HEAD. Which gitattributes have
>     precedence? Again, is order important (i.e., does "diff -R" look at
>     different attributes than "diff")?
>
> I'm sure there are others, too. And I don't think any of these is
> insurmountable. But somebody needs to think through a lot of cases and
> come up with consistent, sane behavior that does the right thing in each
> case (considering both bare repositories and ones with working trees).

I think that diff-index --cached or when there is no working tree,
should set the direction to GIT_ATTR_INDEX so that it may be used with
a bare repo. In such case, the .gitattributes would come from the
index.

Consistent with that, when comparing two commits (diff-tree), I think
you look at the .gitattributes in the second commit.

j.