bug#23534: Failing to recognize -- as comment-starter

[Stefan Monnier]

Package: Emacs
Version: 25.1.50


There's a regression on master where a -- comment-starter fails to be
recognized.  This affects haskell-mode.

Put the following in bug-mode.el:

    (defvar bug-mode-syntax-table
      (let ((st (make-syntax-table)))
        (modify-syntax-entry ?- "_ 123" st)
        (modify-syntax-entry ?\n ">" st)
        st))
    
    (define-derived-mode bug-mode prog-mode "BUG"
      "Major mode to exhibit the bug."
      (setq-local font-lock-defaults '(nil))
      (insert "-- hello\n"))

And then

    emacs -Q -l bug-mode.el -f bug-mode

In Emacs-24.5 (and emacs-25) you then see "-- hello" highlighted as
a comment, but on "master" this stays in default face.


        Stefan




In GNU Emacs 25.1.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.9)
 of 2016-04-17 built on alfajor
Repository revision: 330dcb8fa9dc04fa6b95550774c654435f470277
Windowing system distributor 'The X.Org Foundation', version 11.0.11802000
System Description:     Debian GNU/Linux testing (stretch)

Configured using:
 'configure -C --enable-checking --enable-check-lisp-object-type
 'CFLAGS=-Wall -g3 -Og -Wno-pointer-sign'
 PKG_CONFIG_PATH=/home/monnier/lib/pkgconfig'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
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  locale-coding-system: utf-8-unix

Major mode: InactiveMinibuffer

Minor modes in effect:
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Recent messages:
Mark set [2 times]
Auto-saving...done
Mark set [2 times]
Auto-saving...done
Saving file /home/monnier/tmp/foo.el...
Wrote /home/monnier/tmp/foo.el
Saving file /home/monnier/tmp/foo.el...
Wrote /home/monnier/tmp/foo.el
Saving file /home/monnier/tmp/foo.el...
Wrote /home/monnier/tmp/foo.el

Load-path shadows:
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/home/monnier/src/emacs/elpa/packages/ada-mode/ada-mode hides 
/home/monnier/src/emacs/work/lisp/progmodes/ada-mode
/home/monnier/src/emacs/elpa/packages/ada-mode/ada-stmt hides 
/home/monnier/src/emacs/work/lisp/progmodes/ada-stmt
/home/monnier/src/emacs/elpa/packages/ada-mode/ada-prj hides 
/home/monnier/src/emacs/work/lisp/progmodes/ada-prj
/home/monnier/src/emacs/elpa/packages/ada-mode/ada-xref hides 
/home/monnier/src/emacs/work/lisp/progmodes/ada-xref
/home/monnier/src/emacs/elpa/packages/seq/seq hides 
/home/monnier/src/emacs/work/lisp/emacs-lisp/seq
/home/monnier/src/emacs/elpa/packages/landmark/landmark hides 
/home/monnier/src/emacs/work/lisp/obsolete/landmark
/home/monnier/src/emacs/elpa/packages/crisp/crisp hides 
/home/monnier/src/emacs/work/lisp/obsolete/crisp

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Memory information:
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