Re: On-branch topic description support?

Elijah Newren [off-list ref] writes:

The cover letter material often includes stuff that would not make
sense for the merge message (e.g. "Rebased this version on master
because of conflicts with ...", "Changes since v3", "I'm a little
unsure of the logic in Patch 5", "Patch 3 might be controversial; take
a look", etc.)  Would there be some kind of syntax for specifying the
part of the cover letter meant to be used in the merge commit message,
or would we just start out with it pre-populating the commit message
and expect the integrator to cull out the irrelevant parts?

Yeah, I wanted to flesh out a bit more details on how this may work
before writing more about it, but what I envisioned would go
something along this line:

 * The authoring side would keep track of the description of the
   topic as a whole plus the description of inter-iteration changes,
   in the empty tip commit.  There may be some convention with a
   minimum mark-up (similar to how an innocuous three-dash line
   serves the "end of the message" marker in a patch e-mail) to
   separate the latter from the former.

 * "format-patch --cover-letter" would take the above, and add
   range-diff etc. that is easier to compute mechanically;

 * "am" may take the above, and keep the whole thing;

 * "merge" would keep the "main topic description" part and strip
   out everything after it, including the inter-iteration comparison
   and the range-diff, most likely by commenting the latter out when
   presenting it to the integrator.  So a lazy integrator can simply
   exit the editor to lose everything other than the topic
   description, and a more careful ones may refer to the supporting
   material to enhance/extend the topic description.