Re: How to embed a hash, tag or branch name?

From: Jakub Narebski <jnareb@gmail.com>
Date: Aug 1, 2009, 13:13 UTC
Message-ID: <200908011513.13016.jnareb@gmail.com>
In-Reply-To: <4A743735.9020806@dirk.my1.cc>

On Sat, 1 August 2009, Dirk Süsserott wrote:

> Am 31.07.2009 11:52 schrieb Mikko Rapeli:
>> On Fri, Jul 31, 2009 at 02:27:50AM -0700, Jakub Narebski wrote:

Show 16 quoted lines

>>> You can embed SHA-1 of a _file contents_ (blob) using '$Id: $' keyword
>>> with `ident` attribute - see gitattributes manpage.
>> 
>> Great, thanks!
>> 
>>> The correct solution of embedding version number is to do it at 
>>> _build time_, using e.g. script similar to GIT-VERSION-GEN used by
>>> Git itself and by Linux kernel.  It helps if you tag your releases.
>> 
> 
> Hi Mikko,
> 
> I don't know whether you want to use the "ident" command on your final
> binary. With Git, that's pointless, as all source files will have the
> same $Id$. So it's perfectly sufficient to have only ONE file enriched
> with Git's SHA1.

You are wrong. In Git $Id$ / $Id: $ expands to SHA-1 id of _blob_ (i.e. of file *contents*), not SHA-1 id of a commit. This way when switching branches or rewinding branch using git-reset we don't have to pay huge performance penalty because of `ident`, as we would have because every file would have to be changed if $Id$ was about commit id (or if there was $Revision$ or $Author$ implemented).

> Suggestion: During build time, compile (and link in) a file (e.g.
> version.c) with "-DVERSION=\"$(git describe)\"". My version.c looks like
> this:

GIT-VERSION-GEN and various tricks in Makefile do just that, not only for compiled parts, but also for scripts.

[...]

-- 
Jakub Narebski
Poland