In case it matters, I'll soon also take a look at this.

Soon because I'm currently a bit frustrated by all the things that don't 
work on my system here, or don't work as I would expect.  It started 
today by debbugs.el not displaying all messages under this bug report 
that I can see under the bug on the web, and me not finding any way to 
force it to load all messages.  And it continued that way the whole 
morning...

Ca-tas-tro-phy.

Whatever.

Is it correct that the differences in your branch are that small?  I 
see, in the summary of Magit's equivalent to "git diff master..." only

13 files changed, 114 insertions(+), 79 deletions(-)
doc/emacs/emacs.texi             |  1 -
doc/emacs/trouble.texi           | 59 -------------------------------
etc/NEWS                         | 24 +++++++------
lisp/{ => obsolete}/longlines.el |  1 +
src/buffer.c                     | 10 ++++++
src/buffer.h                     |  4 +++
src/composite.c                  |  6 ++++
src/dispextern.h                 |  5 +++
src/lisp.h                       |  2 ++
src/search.c                     |  2 +-
src/window.c                     |  2 +-
src/window.h                     |  1 +
src/xdisp.c                      | 76 
++++++++++++++++++++++++++++++++++++----

I'm on

*Head:     66704fbbcf Fix typo in e7b5912b23.
*

That's only ~100 lines of code?  Can that be?  I'm suspecting that I 
don't use Magit right, again.  Or something.

Also, would it be a good idea to rebase the branch on master?  That 
would make it possible for me to run the branch OOTB with ASAN.  I did 
that locally here, because I don't want to interfere with your work, so...