Re: n-heads and patch dependency chains

[Sam Vilain <sam@vilain.net>]

Jakub Narebski wrote:

>First, hydras or n-head was invented to avoid capping and recapping, and
>just advance it as a normal head (and to remember what are
>subprojects/patch dependency chains/whatever to choose).
>
>Second, we could generalize those extra commit references in commit
>structure (be they "bind", "prior" or "previous", or "depends-on") and have
>  
>

Note that these are all quite different types of references. "Bind"
implies an unmerged tree to be woven in on checkout, "prior and
"previous" a historical relationship, and "depends-on" the previous
commit that the change that this commit supplies was based on.

So, I think "parent" already means "depends-on" closely enough.

>commit/merge pluggable helper manage them. And merge strategy may make use
>of them.
>
>Third, would using *directory* with for a N-HEAD (containing all the
>subheads, subprojects, chains, branches, fibers, whatever) instead of an
>ordinary file for HEAD be a good idea? For hydra if we want it to be easily
>interweaved with ordinary commit I think we would also need the link for
>bottom, hydra shoulder, hydra tail i.e. common commit being starting point
>for all the chains, or subprojects (for subprojects it can be empty tree
>commit).
>  
>

This was similar to the original suggestion, of heads that have multiple
heads, or hydra. I think the basic rejection for this is that nothing is
then tracking the progression of the merged tree - unless you keep a
"cherry picked" tree for the combined work. And of course it is a
backwards incompatible change.

Sam.