bug#59828: Fundamental Mode buffers fail to keep text properties

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 05 Dec 2022 13:49:28 +0000
> From: Heime <heimeborgia@protonmail.com>
> Cc: casouri@gmail.com, 59828@debbugs.gnu.org
> 
> > > > > Have noticed that when I insert text with colour properties in a buffer
> > > > > using fundamental-mode, the text properties (e.g. colours) get lost.
> > > > 
> > > > I assume you used the ‘face property, right? If you replace ‘face with 'font-lock-face, does it work?
> > > > 
> > > > Yuan
> > > 
> > > I used 'font-lock-face and did not work.
> > 
> > 
> > Please show the code you used. It works here.
> 
> 
> (with-current-buffer (get-buffer-create bufrn)
>   (insert (propertize "G"
>              'font-lock-face '(:background "green"
>                                :foreground "black"))))

From the ELisp manual:

  ‘font-lock-face’
       This property specifies a value for the ‘face’ property that Font
       Lock mode should apply to the underlying text.  It is one of the
       fontification methods used by Font Lock mode, and is useful for
       special modes that implement their own highlighting.  *Note
       Precalculated Fontification::.  When Font Lock mode is disabled,
       ‘font-lock-face’ has no effect.

Note the last sentence.

Conclusion: you need to turn on font-lock in that buffer.