On Sun, Apr 24, 2011 at 2:05 AM, Andrew Coppin
I've discovered something interesting.
Darcs stores history as a partially-ordered set of changes. This is a beautiful and elegant idea. In theory, this lets me apply any combination of changes, possibly generating file "versions" which have never actually existed before. (E.g., the new type checker from GHC 7.0 embedded in the GHC 6.6 codebase - not that I imagine it would compile, but in principle I can do it.)
So I was a little surprised to discover that... Darcs doesn't actually support doing this. Darcs is only really interested in the result of applying *all* changes in a repo. If you want to apply some subset of changes, you need to make a seperate repo containing only the changes you want applied.
It seems daft to me that you would design a sophisticated system for splitting history into independent chunks, and then not let me manipulate them independently.
This is because of a deliberate choice that was made by David Roundy. In darcs, you never have multiple branches within a single darcs repository directory tree. To get the effect you want, you simply create two repositories. One having only the patches for ghc 6.6 and one having the patches of ghc 7.0 and then you pull just the patches you want from 7.0 into 6.6. There are options to 'darcs get' that help you select the right set of patches to help you create the two repositories. If you're interested in the details of how to do it, I would suggest asking on the darcs-users mailing list. Jason