Re: [PATCH] convert filter: supply path to external driver

Pete Wyckoff [off-list ref] writes:

Filtering to support keyword expansion may need the name of
the file being filtered.  In particular, to support p4 keywords
like

    $File: //depot/product/dir/script.sh $

the smudge filter needs to know the name of the file it is
smudging.

Add a "%s" conversion specifier to the gitattribute for filter.
It will be expanded with the path name to the file when invoking
the external filter command.

Signed-off-by: Pete Wyckoff <redacted>
---

pw@padd.com wrote on Sat, 18 Dec 2010 17:38 -0500:

quoted

I'm using git-p4 to import and work with upstream p4
repositories.  Some of the files are ktext, meaning they expect
expansion of $Id$ and similar identifiers.

Using the filter driver for this file, I can do the "clean" part
easily, but to calculate the "smudge" correctly, I need to know
the filename inside the filter driver.

This works fine for me.  It is backward compatible, and leaves
open the possibility of adding other % modifiers if we find
a need later.

This is not backward compatible for people who wanted to use '%' literal
on their filter command line for whatever reason, so please do not
advertise as such.  A fair argument you could make is "Even though this is
not strictly backward compatible, it is very unlikely that people passed a
literal % to their filter command line, and the benefit of being able to
give the pathname information would outweigh the downside of not being
compatible", and people can agree or disagree.

I am personally moderately negative about $any expansion$ (I don't use it
myself, and I don't think sane people use it either).  As far as I can
tell, this should has no impact on the correctness and very little impact
on the performance for people who do not use $any expansion$, so I am Ok
with the patch.

Modulo one worry.  Don't we have, or don't we at least plant to allow us
to have, a facility to cache expensive blob conversion result, similar to
the textconv caching?  How would this change interact with two blobs that
live in different paths?