bug#39597: 27.0.60: M-x occur adds fontification to fundamental-mode

[Kévin Le Gouguec]

Hello,

I think commit fb16313025 (2018-12-18T23:10:09Z!juri@linkov.net) had an
unintended side-effect on fundamental-mode.  From emacs -Q:

- C-x b repro RET
- foo RET "bar" RET baz
- M-s o . RET

In emacs 26.3, the Occur buffer pops up and not much else happens;
starting with emacs 27, font-lock-string-face is applied to "bar".

I haven't dug much more than that; FWIW however, emacs 26.3 already
applied font-lock-string-face to double-quoted strings when running
(font-lock-ensure) in a fundamental buffer, so maybe the right fix
belongs e.g. somewhere in font-lock-set-defaults?


Thank you for your time.


In GNU Emacs 28.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.5, cairo 
version 1.16.0)
 of 2020-01-31 built on hirondell
Repository revision: d3ead375092e2690c1d1d6a5dd82e6e89cdf4f4c
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Configured using:
 'configure --with-xwidgets --with-cairo'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS XWIDGETS
LIBSYSTEMD JSON PDUMPER LCMS2 GMP