Re: [PATCH/WIP] attr: make attributes depend on file type

[Jeff King <peff@peff.net>]

On Mon, Feb 28, 2011 at 04:26:18PM +0100, Michael J Gruber wrote:

> This is a whether balloon patch (to check whether this balloons or not,
> uhm). Hit it hard, not me ;)

Ouch.

> It's part of the way to revive the old idea of making attributes depend
> on file type. I am not following the old path
> 
> pattern is_symlink otherattr
> 
> because that would mean something which looks like an attribute
> (is_symlink) but is not. Instead,
> 
> symlink:pattern attrs
> 
> is to specify attrs for pattern if it is a symlink. So, e.g.,

This is way better than what I proposed. From the user's perspective, it
is visually clearer that the symlink bit is part of the selector, and
not an attribute. And it syntactically disallows nonsense like:

  pattern is_symlink is_gitlink otherattr

The only downside is that it is technically a regression if somebody was
using gitattributes for the bizarrely named file "symlink:". It seems
pretty unlikely, but possibly we should be carving out a syntactic
namespace like:

  ^[a-z]+:

or even:

  ^[a-z]+(=[^:]*)?:

And that would later allow stuff like "submodule:" if people wanted to
attach specific bits to submodules (though perhaps it is not necessary,
because we have the entire separate .gitmodules file). I don't know if
there are other non-name elements people would be interested in
selecting on. So maybe that is over-engineering.

We also need some way of quoting. Duy has a 1.8.0 proposal to handle
this. If we're going to make a syntactic change to gitattributes for
this, it should probably be related (since the quoting mechanism is the
way you would fix it if you _are_ affected), and should probably follow
the same migration mechanism (it looks like there is talk of a "#
feature: foo bar" line).

See:

  http://article.gmane.org/gmane.comp.version-control.git/165970

I didn't test, but do we now assume that a pattern like "foo.*
diff=bar" will only match when foo is a regular file? I think that would
fix stuff like "*.pdf merge=pdf" when there is a symlink named
"file.pdf", which I'm pretty sure is currently broken (but did not
test).

OTOH, that is yet another behavior change if somebody had something like
"foo diff=symlink", which we would be breaking. So perhaps we will need
many "# feature" markers to make this right. :)

-Peff