Profiling Slowdown when Opening Message with Many Threads

[Cole Lyman]

Hi all,

First of all, thank you so much to all of the developers that have
contributed to notmuch. I think it is a beautiful piece of software and
it has certainly made my life better.

I have an email with about 16 threads (responses back and forth 16
times, there are some pdf attachements thrown in there as well) that
takes considerable time (30 seconds to a minute) to open up using the
notmuch Emacs interface. As an aside, there are also some HTML emails in
there which I have read could be the culprit.

I have run the Emacs profiler and have attached the profiler report.
>From viewing the results from the profiler, it seems that there
recursive calls to `notmuch-show-insert-thread` (one call for each
thread, I presume) and as I follow the calls down the stack it turns out
that the function `indent-rigidly` takes up 63% of the CPU cycles.

Anyone have any insight as to why this is happening or next steps that I
could try to debug this?

I am running Emacs 26.1 (with Doom, in case that matters, in the call
stack the `+mail/notmuch-show-reuse-buffer` is part of Doom) on OSX
version 10.14.1. Please let me know if any other information would be
useful!

Thank you,
Cole