[darcs-users] darcs patch: Add Patch-salt as ignored prefix

zooko zooko at zooko.com
Wed Oct 8 16:53:34 UTC 2008

following-up to my own note:

On Oct 8, 2008, at 10:42 AM, zooko wrote:

> See what I mean?  That's the key concept of "out-of-band
> signalling".  Make it so that the metadata which darcs adds and which
> darcs parses and hides and uses is completely separate from the patch
> comment that the user edits, and make it so the two cannot be
> confused with one another.

Basically, what I would *really* like is if darcs had a way to put  
arbitrary key-value pairs into the patch description such that old  
versions of darcs would ignore key-value pairs whose keys they didn't  

Then, we could put "patch-salt" as a key and the salt as a value, it  
would be completely separate from the patch comment (as it should  
be), and old versions of darcs would simply ignore it.

However, old versions of darcs don't do that.  If you put a new field  
into their patch metadata then they croak with an error.  Therefore,  
the only place where we can stick the patch salt is into the only  
arbitrary-length field in the darcs metadata, which happens to be the  
patch comment.

However, our goal should be basically to redefine the patch comment  
so that in the future there are two separate chunks of data in the  
patch comments: the user-editable, user-visible part which serves the  
same purpose that the patch comment has always served, and the  
arbitrary key-value-pairs part which serves as a place where future  
versions of darcs can exchange new fields with each other without  
hopelessly confusing darcs 2.1.0 when it sees patches containing  
those new fields.

Make sense?

For what it is worth, this is a progression of extensibility and  
backwards-compatibility and graceful-upgrade that I have observed and  
participated in several times before.  It's a fairly normal process  
that darcs is going through.  :-)


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