Subject: 25.1.50; cua-mode does not interact with cursor-face and themes well

From: "Jeremy T. Braun" <[email-masked]>
Date: Fri, 29 Apr 2016 11:19:06 -0700

I've had issues where themes couldn't change cursor colors.  I finally
figured out the culprit, cua-mode.  Details on what I noticed and how I
found it follow.

I believe the "correct" way for themes to interact with the cursor color
is to modify the :background attribute of the face named cursor.  See:
https://www.gnu.org/software/emacs/manual/html_node/emacs/Cursor-Display.html

cua-mode defines a variable cua-normal-cursor-color.  By default this is
set to one of initial-cursor-color, cursor-color from initial-frame-alis
or default-frame-alist, the frame-parameter 'cursor-color, or "red" if
those are all not true.

When cua-enable-cursor-indications is enabled, cua--update-indications
is run as a part of cua--post-command-handler, which is added to
post-command-hook.

When run, cua-enable-cursor-indications typically calls set-cursor-color
to one of the cua-*-cursor-color variables.

The result?  Themes can change the cursor-color (via the face or via
set-cursor-color, but after they are loaded/run, the post-command-hook
eventually runs cua--update-indications, which overwrites the theme's
new "normal" cursor color with whatever was previously stored in
cua-normal-cursor-color (for "normal" buffers, anyway).

I first noticed this because I run emacs in --daemon mode a lot.  When
emacs is in --daemon mode, I think that .emacs/init.el is run in the
frame/context of the terminal or background emacs process. When my
init.el is run, (frame-parameter nil 'cursor-color) returns "white",
which cua-normal-cursor-color is set to.  When I switch between the
background-mode = dark/light color themes linked below, the cursor
always stays white, and it's illegible in the "light" theme.
https://github.com/sellout/emacs-color-theme-solarized

When I launch emacs without --daemon, my init.el loads the theme first,
which sets frame-parameter.cursor-color to #839496, which initializes
cua-normal-cursor-color, which is legible in both dark and light modes.

I'm not sure how "best" to fix this.  Options I see:
* Change documentation on custom themes, requiring that in addition to
   modifying the cursor face, they should also modify cua-*-cursor-color.
* Change cua-mode to be aware that themes may modify the cursor face,
   and either update cua-normal-cursor-face to reflect the cursor face's
   :background attribute, or maybe have cua--update-indications use
   something like:
     (or cua-normal-cursor-face (grab the :background attribute of 
cursor-face))
   And then the user can set/customize cua-normal-cursor-face to nil to
   allow the theme to control it.
* Document this, and require the user to hook theme loading and
   after-make-frame-functions to update cua-normal-cursor-color to be
   (frame-parameter frame 'cursor-color), which would have been set by
   the theme at that point.
* Other?

Thanks,
Jeremy

In GNU Emacs 25.1.50.2 (x86_64-pc-linux-gnu, GTK+ Version 3.10.8)
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