Re: gcc_release script, snapshots, and LAST_UPDATED version

[Gerald Pfeifer <gerald@pfeifer.com>]

On Mon, 20 Dec 2010, Joseph S. Myers wrote:
>>>  It's LAST_UPDATED, not LAST_CHANGED.  This is significant; the 
>>> revision number is indeed the revision at which the source tree was 
>>> last updated, not the revision at which the branch was last changed.
>> OK.  How is LAST_UPDATED more useful than LAST_CHANGED?  I would have
>> thought that it would be useful to know the last version on the branch
>> that is being snap-shotted.
> I think you should be doing your own interrogation of SVN information in 
> your snapshot script.  This file is for convenient identification of 
> checkouts for the use of scripts such as contrib/test_summary; the 
> information it contains is already formally redundant (both revision and 
> date, in different time zones).

I'm afraid you lost me here.  Given the example Gary used

   svn info -r167957 file:///svn/gcc/branches/gcc-4_5-branch
   Path: gcc-4_5-branch
   URL: file:///svn/gcc/branches/gcc-4_5-branch
   Repository Root: file:///svn/gcc
   Repository UUID: 138bc75d-0d04-0410-961f-82ee72b054a4
   Revision: 167957
   Node Kind: directory
   Last Changed Author: rguenth
   Last Changed Rev: 167948
   Last Changed Date: 2010-12-16 06:34:03 -0800 (Thu, 16 Dec 2010)

why do we want to use Revision: and not Last Changed Rev: to describe
the branch and accordingly make the following change to gcc_snapshot?

   -  SVNREV=`${SVN} info "${SVNROOT}/${SVNBRANCH}"|awk '/Revision:/ {print$2}'`
   +  SVNREV=`${SVN} info "${SVNROOT}/${SVNBRANCH}"|awk '/^Last Changed Rev:/ {print $4}'`

> It is not meant to contain everything that could possibly be of use in 
> describing a checkout, and certainly not everything relevant for making 
> a snapshot decision (for normal GCC snapshots, you might want to skip 
> them if only the DATESTAMP file - checked in - had been updated since 
> the last snapshot).

Isn't that backwards?  Should we not simply avoid updating DATESTAMP
if there have not been any changes since it's last update?

I'd love to improve this, just right now I'm simply a bit confused,
so any help, clarity or patches would be great.

Gerald