Merge tracking idea

While in the shower this morning I had an idea about how merge tracking
could be implemented in Subversion which would offer a great deal of
advantages.

I know that this may have already been considered, but in case it hasn't
I may as well write it down and post it in case it's useful.

The problems I can see are:

  * Merges in SVN are actually just regular changesets, and therefore
look like any other change. Subversion has no way of knowing whether a
given changeset was a merge or just a change.
  * Subversion doesn't know what changesets have been merged to a given
branch from anywhere else.
  * Merging destroys history. If I merge from a branch that many
developers have worked on to trunk, all of the changes will appear to
have been made by me. svn blame will have my name written all over it:
the original authors recieve no credit (or flack) whatsoever.
  * Merges take up space in the repository, even though the deltas
applied already exist in the repository (on the source branch).

My idea to fix all of these problems is to allow a changeset to
reference another changeset (or list of changesets).

For example, say you have trunk which represents production and a
feature branch. Several developers work on the feature branch, making
several commits.

When performing the merge to trunk, Subversion would examine the
changesets on the branch and which of those had already been merged from
that branch, and compile a list of changesets. Subversion then commits a
changeset containing the new revisions, recording them against the
trunk. When developers update, it references the changesets in the merge
changeset and applies the deltas.

svn blame now also knows who wrote every line originally: full history
is maintained because history is referenced, instead of being copied.

Less space is taken up because you're just referencing changesets
instead of storing entire deltas again.

Now say there's a merge from trunk to branch. More work is done, and
again they merge from branch to trunk,

This time, the branch contains a changeset that is a merge from trunk.
Subversion knows that the changesets referenced by that merge are
already on the trunk, so it doesn't merge them again.

Thoughts, comments?

-- 
Russ.
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