Re: Making a non-ASCII space character visible

[Will Parsons <varro@nodomain.invalid>]

On Sunday, 17 Jun 2018  9:40 PM -0400, Nick Helm wrote:
> On Mon, 18 Jun 2018 at 08:28:18 +1200, Will Parsons wrote:
>
>> I sorry if I seem to be a bit dense here, but if
>> global-whitespace-mode doesn't enable whitespace-mode globally, what
>> is it good for?
>
>> So, adding (whitespace-mode 1) to my ~/.emacs file is useless unless I
>> add it to a major-mode hook, and that I have to do that for every
>> major-mode I use?  I can't just say "enable whitespace-mode for all
>> buffers unless I say otherwise" then?
>
>> I'm afraid I'm completely lost here.
>
>> Apart from how to enable whitespace-mode automatically, I'd like to
>> understand how that:
>>
>> 1) The character u+2007 (8199) has been verified to have been added to
>>    whitespace-display-mappings.
>>
>> 2) Even after running manually M-x whitespace-mode and verifying that
>>    the variable whitespace-mode is now set to t, the display of u+2007
>>    doesn't change in the current buffer.
>
> Think of whitespace-mode and global-whitespace-mode as two different modes. 
>
> Doing M-x whitespace-mode will show whitespace chars only within the buffer that
> was current when when you called the command. Doing the same command a second
> time will toggle whitespace-mode off again. When a window shows a buffer that has
> whitespace-mode active, "ws" (lower case) will appear in the mode-line.
>
> Doing M-x global-whitespace-mode will show whitespace chars in all buffers (with
> a few exceptions). Doing the same command a second time will toggle
> global-whitespace-mode off again in all buffers. When global-whitespace-mode is
> active, "WS" (upper case) shows in all mode-lines as it is active in all
> buffers.
>
> The two modes work cooperatively, so you can, for example, turn on
> global-whitespace-mode everywhere, then toggle whitespace-mode off to hide
> whitespace chars in a particular buffer.

That makes sense, and is kind of like what I would have expected.

> There are also two variables with (confusingly) the same names as the functions
> that control the modes, i.e. whitespace-mode and global-whitespace-mode. Ignore
> these variables for now, they cannot control the modes, only tell you what state
> each mode is in.

Yes - I had managed to figure that out.

> When enabling the modes from lisp, it works slightly differently. You need to
> call the functions `whitespace-mode' and `global-whitespace-mode' with an
> argument to turn the modes on and off. For instance, if global-whitespace-mode
> is off and you evaluate this (using C-x C-e):
>
>   (global-whitespace-mode 1)
>
> Emacs will turn the mode on in all buffers. Evaling it again will have no effect
> as the mode is already active. To turn it off, you would eval:
>
>   (global-whitespace-mode -1)
>
> Similarly, if you want to turn on whitespace-mode in a particular buffer, you
> need to eval the function within the buffer you're interested in. For example,
> evaling this in *scratch* will only turn it on in *scratch*:
>
>   (whitespace-mode 1)
>
> This is why adding (whitespace-mode 1) to your ~/.emacs file by itself doesn't
> work. Emacs has activated the mode in whatever buffer happened to be current
> when it started up, which is unlikely to be a buffer you're interested in. So to
> active it automatically everywhere all the time, you would add:
>
>   (global-whitespace-mode 1)
>
> to your ~/.emacs file. Or, if you want to activate it only for specific modes,
> you would use a mode hook to turn on whitespace-mode just for buffers that use
> that specific mode.
>
> However, because you want to visualise some non-standard characters, before you
> turn on either of the whitespace modes, you need to tell Emacs what you want it
> to display. That's what the variable whitespace-display-mappings is for. This is
> a global variable, it's value is the same regardless of whether you're using
> whitespace-mode or global-whitespace-mode.
>
> As you've already worked out, you would change this variable to remap the char
> you're interested in, but you need to make sure you set the variable before you
> turn the mode on. So you would have something like the following in your
> ~/.emacs:
>
>   (setq whitespace-display-mappings '((space-mark     32 [183] [46])
>                                       (space-mark    160 [164] [95])
>                                       (space-mark   8199 [164] [95])
>                                       (newline-mark   10 [36 10])
>                                       (tab-mark        9 [187 9] [92 9])))
>   (global-whitespace-mode 1)

This is valuable information.  I see that I got that wrong in that I
had:

  (global-whitespace-mode 1)
  (setq-default whitespace-style '(face lines-tail tabs trailing))

in the body of my ~/.emacs file, but that I had:

  (setq custom-file "~/.emacs.d/custom.el")
  (if (file-exists-p custom-file)
      (load-file custom-file))

at the very end, and that I had put the setting of
whitespace-display-mappings in ~/.emacs.d/custom.el.

> In addition to the defaults, this tells Emacs to map FIGURE SPACE (8199) to
> CURRENCY SIGN (164) when either whitespace-mode or global-whitespace-mode is
> active. BTW, if you want to visualise the FIGURE SPACEs differently you can
> change the 164 in (space-mark 8199 [164] [95]) to the codepoint for whatever
> char you like.
>
> That should be all you need to get this working. Normally, you could do all this
> through customize, but as pointed out up-thread, this isn't working as expected.
> Fortunately, you can do this entirely in your ~/.emacs file with the lines
> above, but it might pay to temporarily disable any other settings related to
> whitespace in your custom.el and ~/.emacs while you get things working.

OK - I have now modified my .emacs file to have the following lines:

-------
(setq whitespace-display-mappings '((space-mark     32 [183] [46])
                                    (space-mark    160 [164] [95])
                                    (space-mark   8199 [164] [95])
                                    (newline-mark   10 [36 10])
                                    (tab-mark        9 [187 9] [92 9])))
(global-whitespace-mode 1)
(setq-default whitespace-style '(face lines-tail tabs trailing))
-------

I have removed the setting of whitespace-display-mappings that I had
previously manually introduced to custom.el, and the only other
setting that appears to reference whitespace is the setting

  (whitespace-tab ((t (:background "#081820" :foreground "darkgray")))

in my custom.el file, which I have now removed.

Unfortunately, after making these changes, and having restarted Emacs,
there is still no change to the display of u+2007.

Despite my frustration about not achieving my aim, I thank you for
your very detailed explanation of the relationship between
whitespace-mode and global-whitespace-mode, which, although it hasn't
actually led me to a solution to my problem, has been very helpful for
my understanding of how whitespace-mode works.

-- 
Will