Advicing select-windows, shr rendering, and per-buffer-theme package

["Iñigo Serna" <inigoserna@gmail.com>]

Hi,

I'm the author of “per-buffer-theme”, a simple package available in
MELPA [1], which changes emacs theme when switching to a buffer according to
some configured rules (f.e. use a dark theme when coding, light theme
for email or web navigation). It advices `select-window', checks buffer
name or major-mode, and changes theme.

It worked correctly and fast with emacs 24.5, but now with emacs 25.x it
produces additional “flickering” when switching buffers, especially for
eww/shr buffers, where it makes package useless.

I think problem comes that, when switching to a eww/shr buffer, shr
rendering uses many temporal buffers, so theme changes many times
producing that "flickering" effect. But I'm not sure as my elisp skills
and emacs internals knowledge is quite limited.

I don't know how to solve it… I've tested with before/after variations
to `advice-add' but results are similar. First versions used
`window-configuration-change-hook' but add-advice to select-window was
much better option then. Any ideas?

Thanks in advance,
Iñigo Serna

[1] http://melpa.org/#/per-buffer-theme
    https://bitbucket.org/inigoserna/per-buffer-theme.el