Font Lock on-the-fly misfontification in C++

[Marshall, Simon]

This bites on a frustratingly regular basis.  Put the following in a
fubar.cpp:

class Fubar :
  public Foo,   // Foo fontified as a type, at first
  public Bar    // Bar fontified as a type, at first
{
  Foo bar(Snafu snafu,  // Types, function, variable fontified, at first
          Foo foo,
          Bar bar);
  Foo bar(Snafu *snafu, // Types, function, variable fontified, at first
          Foo foo,
          Bar bar);
};

Then emacs -Q fubar.cpp.  I see Foo, Bar and Snafu fontified as types even
where declaring functions and variables.  The corresponding functions and
variables are fontified correctly.  This is great!

Then do the following.

1.  Append a space to the first (or second) commented line.  Bug:
fontification of Foo (and/or Bar) is removed.

2.  Append a space to the third commented line.  Bug: fontification of Foo
and bar is removed from that line.

3.  Append a space to the fourth commented line.  Bug: fontification of Foo,
bar, Snafu and snafu is removed from that line.

Somewhat spookily, if you then repeat (2), then the fourth commented line
(3) gets fontified correctly after the deferral delay.

I think this is some sort of problem with Jit Lock mode multiline
fontification, at least for (2) and (3), since Lazy Lock mode works ok.  (Of
course, Lazy Lock mode is now depreciated and lazy-lock-mode is not
autoloaded.)

Stefan Monnier kindly posted a possible partial fix (see
http://lists.gnu.org/archive/html/emacs-devel/2006-07/msg01193.html) but
that thread went into a discussion about the font-lock-multiline text
property.  I don't know how valid the approach is now (and obviously the
patch was not checked in).

Simon.


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