Re: [RFC/PATCH 0/2] Color moved code differently

Junio C Hamano [off-list ref] writes:

I do not think you should step outside diff_flush().  Only when
producing textual diff, you would have to run the textual diff
twice by going over the q twice:

 * The first pass would run diff_flush_patch(), which would call
   into xdiff the usual way, but the callback from xdiff would
   capture the removed lines and the added lines without making any
   output.

 * The second pass would run diff_flush_patch(), but the callback
   from xdiff would be called with additional information, namely,
   the removed and the added lines captured in the first pass.
...
   The fn_out_consume() function working in the "second pass of
   moved from/moved to mode" would inspect line[] and see if it is
   an added or a removed line, and then:

   - if it is an added line, and it appears as a removed line
     elsewhere in the patchset (you obtained the information in the
     first pass), you show it as "this was moved from elsewhere".

   - if it is a removed line, and it appears as an added line
     elsewhere in the patchset (you obtained the information in the
     first pass), you show it as "this was moved to elsewhere".

Or something like that.

Actually, the first pass above ends up queuing majority of the diff
output in-core _anyway_, so it would make much more sense not to
rely on the reproducibility of xdiff machinery by not calling it
twice.  Instead, I would imagine that the first pass can queue all
what it receives in the callback, then with the whole-patch picture
at hand, you can call updated fn_out_consume() yourself (instead of
letting xdiff machinery to call you), and that would become the
"second pass".