[Q] How to make text invisible without modifying the buffer?

[Q] How to make text invisible without modifying the buffer?

[Rodrigo Morales]

* Epilogue

I'm writing a mode for reading logs from the weechat IRC client.

Here's an example of a log file from weechat.

#+BEGIN_EXAMPLE
00:04:20	<--	user8  has quit (Quit: leaving)
00:05:06	user1	foo
00:05:29	-->	user4 has joined #foo
00:06:11	<--	user5 has quit (Quit: Client closed)
00:06:24	<--	user6 has quit
00:06:28	-->	user7 has joined #foo
00:06:31	user2	bar
00:07:05	user3	fizz
#+END_EXAMPLE

Note that a tab character is used as the delimiter for timestamps,
user names and the actual message.

I would like to hide those lines that present information of a user
logging in or logging out. That is, those lines that matches the
following regular expression (the regex has been enclosed in double
quotes have been used to indicate that the last character is a tab
character)

#+BEGIN_EXAMPLE
"^[0-9]{2}:[0-9]{2}:[0-9]{2}	(-->|<--)	"
#+END_EXAMPLE

* The question

To begin writing this mode, I was wondering: How to make a line
invisible?  and came up with the following expression which accomplishes
that

#+BEGIN_SRC elisp
(put-text-property (point-at-bol) (+ (point-at-eol) 1) 'invisible t)
#+END_SRC

The problem with this expression is the fact that it modifies the
current buffer and I don't want this to happen, so my question is: How
to make a line invisible without making the buffer to think that a
modification has been performed?

Re: [Q] How to make text invisible without modifying the buffer?

[Emanuel Berg via Users list for the GNU Emacs text editor]

Rodrigo Morales wrote:

> To begin writing this mode, I was wondering: How to make
> a line invisible? and came up with the following expression
> which accomplishes that
>
> #+BEGIN_SRC elisp (put-text-property (point-at-bol) (+
> (point-at-eol) 1) 'invisible t) #+END_SRC
>
> The problem with this expression is the fact that it
> modifies the current buffer and I don't want this to happen

`narrow-to-region'?

  Restrict editing in this buffer to the current region.
  The rest of the text becomes temporarily invisible and
  untouchable but is not deleted; if you save the buffer in
  a file, the invisible text is included in the file. C-x
  n w makes all visible again.

Flirting with not disaster perhaps but ...

-- 
underground experts united
https://dataswamp.org/~incal

Re: [Q] How to make text invisible without modifying the buffer?

[Emanuel Berg via Users list for the GNU Emacs text editor]

Rodrigo Morales wrote:

> I can look into how to make narrow-to-region to work into
> multiple regions but that would prensent the XY problem,
> where X is "How to hide entire lines without modifying the
> current buffer" and Y being "How to make narrow-to-region
> work in separated regions"?

https://www.emacswiki.org/emacs/HideLines

-- 
underground experts united
https://dataswamp.org/~incal

Re: [Q] How to make text invisible without modifying the buffer?

[Eli Zaretskii]

> From: Rodrigo Morales <moralesrodrigo1100@gmail.com>
> Date: Fri, 13 Aug 2021 18:39:57 -0500
> 
> #+BEGIN_SRC elisp
> (put-text-property (point-at-bol) (+ (point-at-eol) 1) 'invisible t)
> #+END_SRC
> 
> The problem with this expression is the fact that it modifies the
> current buffer and I don't want this to happen, so my question is: How
> to make a line invisible without making the buffer to think that a
> modification has been performed?

The usual method is to wrap your code in with-silent-modifications.